Pawpaw Ecological Survey in Michigan
with Background Information, Excerpts of Scholarly Papers,
RECOMMENDATIONS for ensuring POLLINATION in Orchards,
and Pawpaw subcanopy thrival despite OVERPOPULATED DEER
Most recent UPDATE: June 2023 by Connie Barlow
ASIMEN is the traditional Potawatomi term(1) SAP-BEETLES (Nitidulidae) are the most likely and abundant effective pollinators. Spring 2021 pollinator survey by Connie Barlow and Dallas Ford confirmed abundance (and extended deep flower habitation mating?) of Glischrochilus quadrisignatus (below left) and the even tinier Stelidota geminata (below right):
Henceforth, "PAWPAW" and "ASIMEN" will be used interchangeably in this project.
Consult the Asimina triloba entry in Wikipedia.
CONCLUSIONS & RECOMMENDATIONS (as of April 2023)
(2) MARC BOONE'S CURRENT HABITAT MANAGEMENT likely offers ideal conditions for LIFECYCLE SUCCESS of the beetles. The most important element for full life-cycle success may be Boone's practice of allowing some post-season fruits to remain where they drop beneath the pawpaw trees, as eggs are laid by the beetles in rotting fruit. (See photos below.) There the larvae feed, pupate, and emerge as beetles in time to burrow into the ground before winter freeze. Possibly his practice of putting wood chips beneath the trees ensures undisturbed and insulated winter habitat. As to POLLINATION SUCCESS, Boone currently achieves sufficient wild pollination, without installing carrion as a lure.
• REMAINING QUESTIONS: Given that pawpaw fruit begin to ripen in September, and that no insects seem to utilize the developing fruit for egg-laying and larval development, what do the adult beetles do post-flowering and during the summer?• What plants do the beetles eat during the summer, and where does the pollinating generation of nitidulid beetles deposit their eggs?Specifically, what rotting fruits are available in Michigan in spring or early summer? Could wild strawberries have been the co-evolved food source for Stelidota beetle larvae? Then, possibly wild raspberries. As for the larger Glischrochilus, it is now well established as using rotting corn cobs for oviposition and for overwintering as adult beetles as deep as 15 cm into the farm soil. Does this beetle also find good egg-laying habitat in the fallen orchard apples that continue rotting in the spring? (Advance to the "Habitat management" section for more information and references.)
VIDEO DOCUMENTATION OF FIELDWORK (as of April 2023)ABOVE: 36-minute VIDEO by Connie Barlow documents 60 fruits ripening in the large pawpaw patch along the Saline River on 9 September 2021.ABOVE: 59-minute VIDEO by Connie Barlow aggregates excerpts of fieldwork videos during the flowering season (May 2021 and 2022); posted on youtube April 2023.
COLLECTING & DISTRIBUTING SEEDSABOVE: November of 2021 and 2022, Connie Barlow collected some post-harvest green and rotting fruit at Marc Boone's pawpaw orchard near Ann Arbor, MI.
ABOVE LEFT: Seed harvests from horticultural plantings autumn 2021 and 2022 were winter stratified in pits dug into a forested slope in Ypsilanti. No germination was evident in the cool soil when the seeds were dug up end of May in 2022 and 2023. WINTER STRATIFICATION of 2021 seed harvest = 750 seeds from Marc Boone's orchard and 400 seeds from Joe Grant's orchard. WINTER STRATITFICATION of 2022 seed harvest = 1,000 from Marc Boone orchard and 140 from Monica King's in Ypsilanti.
ABOVE CENTER: Distribution of seeds in June 2023 included 3 land conservancies in the Traverse City area of Michigan that recently began participating in the "Assisted Tree Range Expansion Project", by which private forest owners began planting 6 new tree species whose northern-most ranges are southern Michigan. (Pawpaw is now a 7th species.) DISTRIBUTION of 2021 seeds (during JUNE 2022) to individuals in these states: MI, NY, DE, PA, and IL. Seeds numbering in the hundreds were sent to individuals in 3 tribes northward of pawpaw's historical range: Onondaga (Syracuse NY), Odawa (Harbor Springs, MI), and Ojibwe (Hayward, WI). DISTRIBUTION of 2022 seeds (during JUNE 2023) entailed Little Traverse Bay Bands of Odawa Indians, ATREP, and private forest planters in Ottawa and Nova Scotia.
ABOVE RIGHT: Connie Barlow contributed a lot of new material and editing to the Asimina triloba WIKIPEDIA page, which included the picture, information, and links to the citizen initiative in Pennsylvania that plants pawpaw along the Allegheny River as a means for bringing the Zebra Swallowtail back to Pittsburgh.
OTHER ANATOMICAL FEATURES OF PAWPAWPawpaw fruit (wild types and most cultivars) tend to remain green or become blotched with brown when at peak ripeness. Rotting then proceeds quickly, advancing skin color to fully brown and reducing the shelf life of this fruit thereby restricting commercial sale of this fruit to its regional habitat.
Green skin is retained while ripening likely for three reasons:
(1) Because this fruit co-evolved for seed dispersal by large mammals, fruit color is no signal for suggesting ripeness to its intended seed dispersers. Mammals (other than primates) rely on olfactory rather than visual clues for discerning ripe fruit.
(2) Unlike apples, pawpaw fruit does not have a core by which nourishment arrives for growing and ripening seeds. Instead, pawpaw's green skin enables the fruit itself to conduct photosynthesis. Photosynthates produced in the fruit skin are transferred directly to the developing seeds via thin threads. These threads are easiest to observe in overripe fruit (photo left).
(3) Even after the fruit falls, green skin would enable photosynthesis to continue for the task of hardening the seed coat prior to pulp ripening. This sequence would ensure that seeds pass through a megafaunal digestive tract without injury.
LEFT: Improper germination of pawpaw seeds in a shallow pot.
Because the large seeds contain enough energy to produce a long taproot prior to seeking photosynthetic opportunities above ground, the seed itself will be pushed upward and into the air if germinated in standard pots which is not a healthy outcome.
In contrast, when a seed is planted where the taproot has free range to grow very long, the lengthening taproot may represent the entire first-year growth. No above-soil stem emergence may be visible until the following year.
This taproot-dominance is one reason why attempts to transplant pawpaw seedlings, or sell them in nurseries, so often fail.
ABOVE LEFT: A 1998 paper reported no visible sign of germination above ground until Day 50, when "the first true leaves on the seedling emerged." Earlier reports of seedling emergence ranged from 45 to 90 days. "Morphological development of the North American pawpaw during germination and seedling emergence", by C.H. Finneseth et al., HortScience.
ABOVE RIGHT: Connie Barlow experimented with planting pawpaw seeds 4 inches deep in a tall pot and thereby confirmed that a seedling will emerge without pushing the seed itself above the soil.
• 2022 VIDEO WEBINAR by Robert Brannan, Professor of Food Science at Ohio University:
TOPICS BY TIMECODE:
09:00 - cultivars
10:55 - nutritional aspects of pawpaw
36:35 - don't let seeds dry out before planting
37:40 - pulp causes digestive problems in some people
50:25 - sudden ripening and short shelf life
BASIC ELEMENTS OF THE PROJECT
• PRIMARY ORIGINATOR AND ADVOCATE OF PROJECT IDEA: CONNIE BARLOW is a retired science writer, who wrote about pawpaw's loss of megafaunal seed distributors in her 2001 book, The Ghosts of Evolution: Nonsensical Fruit, Missing Partners, and Other Ecological Anachronisms, pp. 105-109.) Since 2014, she has video-documented climate quandaries of various native tree species in the USA and posted these on youtube: "Climate, Trees, and Legacy". Connie says,"As a practitioner of traditional natural history" forms of field observations, I am keen on learning whether this form of qualitative, slow, and open observation might complement quantitative, single-focus forms of modern western science. I am also keen on learning whether this older form of western science might serve as a bridge for appreciating the efficacy and relational richness of TEK, "Traditional Ecological Knowledge." I shall also assess how the results of this study and collaboration might feed into my own advocacy for "assisted migration" of climate-threatened native trees, how Indigenous perspectives would reshape underlying worldviews (as well as suggested actions) in this endeavor, while striving for wider recognition of the Haudenosaunee phrasing "helping forests walk" for appreciating that native peoples in North America have by far the most experience in helping native plants move poleward. Clearly, they have been doing so for centuries (possibly for thousands of years), and asimen is surely one of the beneficiaries."
• SOUTHERN MICHIGAN hosts the three study sites where potential POLLINATORS of pawpaw were observed during the flowering time (May) of 2021 and 2022. Borrowing from the University of Michigan's Land Acknowledgment Statement:"We acknowledge that the University of Michigan, named for Michigami, the world's largest freshwater system and located in the Huron River watershed, was formed and has grown through connections with the land stewarded by Niswi Ishkodewan Anishinaabeg: The Three Fires People who are Ojibwe, Odawa, and Potawatomi along with their neighbors the Seneca, Delaware, Shawnee, and Wyandot nations."
• INSPIRATION FOR LEARNING. Quotation from "Mishkos Kenomagwen, the Lessons of Grass: Restoring Reciprocity with the Good Green Earth", by Robin Wall Kimmerer, chapter 3 in Traditional Ecological Knowledge, edited by Melissa K. Nelson and Dan Shilling, 2018:"... While our fluency with plant knowledge is diminishing, in both Native and non-Native communities, I have been taught that the knowledge itself is not lost. Humans may have forgotten, but the knowledge is resident in the land itself. Thus, knowledge revitalization depends as much on gaining the skills for learning from the land as it does on transmitting specific information. We need to ensure that we are educating people with the capacity to learn from the land again, to retrieve the knowledge that is held for us by the plants.... When plants are understood as teachers, it is an act of reciprocity to be an attentive student and to pass on the teachings of the plants."• TEK ENHANCES WESTERN SCIENCE (SEK): This webpage will embed excerpts from writings on TEK by Indigenous authors. To begin, this from Robin Wall Kimmerer, 2002:"TEK is highly rational, empirical, and pragmatic, while simultaneously integrating cultural values and moral perspectives. With its worldview of respect, responsibility, and reciprocity with nature, TEK does not compete with science or detract from its power but extends the scope of science into human interactions with the natural world."
• GENUS NAME DERIVES FROM INDIGENOUS: Linnaeus originally classified this plant as Annona triloba. Later, Micheaux renamed the species Orchidocarpum arietinum. Four years later, Persoon again transferred the species to Porcelia triloba. Finally, in 1817, Dunal reclassified the plant as Asimina triloba. This final genus name, Asimina, derives from indigenous naming. Asimen is the traditional Potawatomi term. Note that the settled scientific name, Asimina, is effectively a "latinized" version (add the suffix "a") to the spoken Potawatomi word. Henceforth, "PAWPAW" and "ASIMEN" will be used interchangeably in this project.
For more information on name derivation from indigenous languages, see p. 191 in Pawpaw: In Search of America's Forgotten Fruit, by Andrew Moore, 2015.
Table of Topics
keep scrolling or click to advance to topic
• Sites (Fruited and Fruitless) for Field Observations and Comparisons
• Pawpaw as an ancient flower type (CRUCIAL READING FOR SERIOUS OBSERVERS)
• Probable Pollinators of Spring 2021 - Nitulidid Beetles
• APPENDIX: PHOTOS of Spring 2021 surveillance at sites (insects, pawpaw stages, ecology)
• GERMINATION & WILD PLANTING EXPERIMENTS (photo-essay)
• Helping Forests Walk: Assisted Migration of Pawpaw
• PHOTO-ESSAY ON IDEAL HABITAT FOR DIRECT SEED PLANTING
This 2022 UPDATE has so many photos it is posted as a distinct webpage (not on this page).
Sites for Field Observations and Comparisons
USDA Pawpaw page reports: "Pawpaws grow in humid climates and are highly frost tolerant. They grow in the shade in open woods usually in wet, fertile bottomlands, but can grow in upland areas on rich soils." Both types are in this study: SITE 1 is upland; SITE 2 is riverine bottomland.
PHOTOS: Marc Boone Farm by Connie Barlow 2020 (left) and Pawpaw patch in Draper-Houston Preserve by Dallas Ford 2020 (right).
LEFT: Boone Farm pawpaw rows are foreground. RIGHT: Along Saline River, Barlow is touching pawpaw stems.
SITE 1, MARC BOONE FARM: Photo above left early October. Marc planted pawpaw cultivars in rows in 1987. The fully mature, short trees are in foreground, with autumn-yellow leaves. They are in full sun, with mowed lawn that prevents clonal proliferation of non-cultivar rootstock. The orchard now entails about 300 pawpaw trees. It is given no supplemental water(?). Marc reports sufficient wild pollination, though an early spring punctuated by severe frost in 2020 reduced fruiting. Because the fruits are large and heavy, he removes flowers toward the outer reaches of the branches(?) Note: American persimmon cultivars are also grown in full sun on this farm. Marc Boone shows his pawpaw trees in this 5-minute video. See also: "'Nothing as dramatic as the pawpaw': Ann Arbor pawpaw farmer Marc Boone retraces memories through orchard", 26 October 2022, by Roni Kane, Michigan Daily.
SITE 2, DRAPER-HOUSTON MEADOWS PRESERVE: Just west of the city of Milan, the preserve protects over one-half mile of Saline River shoreline, with a quarter mile of continuous pawpaw understory along the higher bank side. Notable large (and old) canopy trees include Swamp White Oak, Hackberry, Sycamore, Cottonwood, Black Ash, and Black Walnut. (Pawpaw, unlike many other subcanopy plants, is well adapted to grow beneath Black Walnut.) Following several site visits, Connie Barlow suggests that pawpaw here is a continuous patch that appears to have fully expanded to all contiguous sites accessible by clonally spreading lateral roots. Lower, swampy domains prevent further extensions.
ABOVE LEFT: Pawpaws nearly ripe at Boone Farm, early October 2020.
ABOVE RIGHT: Many stems at Draper-Houston show vertical cracks; maximal stem diameters about 1 foot, but roots may be centuries old. If such cracks predominate on the southwest side of the trunk, then it is possibly a freeze-thaw-freeze problem for this thin-barked tree, as offered in a comment to this very question: "Sunscald occurs on the SW side of the tree on a cold day. The sun heats the trunk up on the SW side and then passes behind a cloud or hill. The rapid temperature change causes the bark to separate from the tree causing a wound that usually doesn't heal." Indeed, Marc Boone paints the lower portion of his pawpaw trunks white, to reflect sunlight and thus reduce possible winter thaws.
ABOVE LEFT: Pawpaw is easily identified in winter by its flexible furry terminal leaf buds and its round furry flower buds.
ABOVE RIGHT: Stems last perhaps half a century maximum. However, the clone persists and expands via lateral roots extending and then sprouting new stems ("ramets"). Photo here was taken by Connie Barlow at Draper-Houston, autumn 2020.
Counties inhabited by pawpaw, U Michigan data
Both of the study sites sites detailed above are located in WASHTENAW COUNTY, purple star on the left.
SITE 3, JOE GRANT FARM is a bit north of so-called wild or native range. It is the yellow star, Freeland. Joe described his orchard:
"We planted our 1st pawpaws about 15 years ago. We now have about 200 planted with 25 producing fruit. Only 5 of our plants are cultivars. I hang onion sacks with rotted meat in them to attract pollinators. I think it helps. We are pretty far north but have a zone 5 climate. I have been promoting pawpaws whenever I can. We produced 80# of pulp last year that was bought by a brewery. But most of the fruit we tend to give away for educational purposes. We also give away 1-2 yr. old seedlings with instructions."
Green Star is the site of Pokagon Band tribal lands. Fall of 2021, the natural resources director of Pokagon Band (Jennifer Kanine)
Photo by Connie Barlow, 24 September 2021.
LEFT: Fall of 2021, the natural resources director of Pokagon Band (Jennifer Kanine) visited the pawpaw patch twice at Draper-Houston Meadows Preserve.
First was to explore the patch while unripe fruit still hung from the trees and next for gathering fruit in the company of county staff in charge of the preserve's management.
She first communicated with another band and learned:"Nottawaseppi Huron Band has responded and indicated that they would like to be kept apprised of the project, but consider the area historic Potawatomi territory and are fine with Pokagon Band moving forward."
ABOVE: October 6, 2023 Draper-Houston Preserve. Very few pawpaws were ripe yet. This was the biggest cluster we saw; none were ripe. Saline River visible.
STUDY AIMS• 1. Discover why some pawpaw patches produce little or no fruit.
A pawpaw study near Toledo, Ohio (see below), documented large fruitless patches in the wild. Meanwhile, the MARC BOONE Farm near Ann Arbor produces prolific fruit yet insects visiting Marc's pawpaw orchard in bloom have never been carefully observed and identified.
Similarly, JENNIFER KANINE, natural resources staff for the Pokagon Band (Potawatomi) reports large differences in fruit production (including complete absence of fruiting) among wild sites in their local areas of s. Michigan.
Winter 2021 CONNIE BARLOW offered 3 hpotheses:HYPOTHESIS #1. FEW POLLINATORS: Asimen is a classic beetle-pollinated flower, as has been confirmed through careful observation of four sister species of genus Asimina whose native ranges are much farther south. Only one of those sister species, A. parviflora has the same flower type as pawpaw: downward hanging, maroon color, and with an odor described as yeasty or fetid. A. parviflora, however, is smaller than A. triloba (its common name is Dwarf Pawpaw). Known beetle pollinators of genus Asimina may require rotting hardwood standing or fallen trees (such as oak) for their larval stages. Thus, if our citizen watch detects differences in pollinator visitations between the fruiting and non-fruiting sites, a next step will be to determine if differences in rotting wood availability may be implicated or whether agricultural spraying of neonicotinoid pesticides in the area may be implicated.A 1985 paper (citation below) concluded:
HYPOTHESIS #2. INADEQUATE SUNLIGHT: Pawpaw natively is a subcanopy tree of deciduous hardwood forests. It thus can be expected to self-limit flowering to the sunniest stems and branches within a clonal patch and may also halt development of successfully pollinated flowers owing to inadequate sunlight. Observers will be asked to offer their qualitative judgments as to whether access to sunlight seems to explain flowering sites and abundance in their watch area. Perhaps a publishable form of data gathering will be initiated in a follow-up stage of study.
HYPOTHESIS #3. LOW GENETIC DIVERSITY: Pawpaw reproduces vegetatively by sending forth root suckers. Over the course of decades and centuries a single genotype can expand its roots and stems ("ramets") throughout vast subcanopy areas. Scientific research has confirmed that wild patches tend to have very low genetic diversity, despite high diversity between patches. Because inbreeding can be detrimental, plants generally have ways to reduce "selfing" (self-pollination). The flower structure of asimen appears to discourage self-pollination within a single flower. But, as shown below, multiple flowers are in different stages of female receptivity and male pollen-producing on the same tree."Given their strong protogyny [the female stage in flowers begins and ends before the pollen stage] and clonal habit [spread into large patches by underground roots], fertilization may require the arrival of pollen from a considerable distance."This conclusion was based on wild patch fruiting distinctions that the team had documented:Fruit production, however, varied strikingly among the stands. No fruits were produced by any of the 524 trees in the Toledo, Ohio stands. In the Cincinnati stands 11 of the 75 sample trees produced a total of 21 fruits.... Reasons for the total failure of fruit set at Toledo are unclear. Bowden and Miller (1951) concluded that the pawpaw in southeastern Ontario occurs in areas of low elevation that have "sufficiently long frost-free seasons" to permit the development of fruit. However, length of growing season does not seem to account for the failure of fruit set in our stands. At our Toledo sites nearly all flowers hung on the trees to maturity, withered, and fell. Few were aborted prematurely, and official daily minimum temperatures at Toledo's U.S. Weather Bureau during flowering were so far above 0°C that we do not believe frosts could have occurred in our stands. Subsequent visits to site T2 have revealed no fruit set in 1981 or 1982. Apparently the failure of fruiting in Toledo is an annual phenomenon independent of variations in the local climate regime. ... Protogyny combined with highly synchronous flowering and the need for outcrossing would make successful pollination a relatively rare event, especially in the Toledo stands, which are separated from other pawpaws by the distances of several to many km.• 2. Learn about and then look onsite for the source of POLLINATOR LARVAL FOOD (and good overwintering ground habitat) at both horticultural and wild sites.
Citation: "Geographic Variation in Size and Reproductive Success in the Pawpaw (Asimina triloba)", by Renee LaGrange and Elliot Tramer, 1985, Ohio Journal of Science.
Because the planted full-sun orchard at Marc Boone's farm produces fruit in abundance, we can expect to document species and abundance of truly effective pollinators (likely, beetles). Hence, an additional study element will be to locate the microsites at or near Boone's property that serve as home and food for the larval stage of the pollinators. As detailed in the next sections, published sources indicate that pawpaw's pollinating beetles do not lay their eggs (and thus feed their larval stage) on carrion or dung. Rather the beetles seek out rotting hardwood trees and logs (or wood chips or leaf mulch thereof).
• SEPT 7, 2021 report by Marc Boone:"... There will be some u-pick pawpaws this fall, not as much as I hoped, probably because we had a late frost that killed most of the flowers. This is the second year in a row that we had this happen, and only the second time in 25 years. Hopefully we can go for another 25 without late frost.
Pawpaw as an Ancient Flower Type
A literature search that begins with the genus Asimina misses crucial evidence for understanding the identity of likely pollinators and the specific floral attributes that co-evolved to ensure pollination. Instead, one should begin by reading what has been discovered about pollination within the higher taxonomic level, the family:
FAMILY ANNONACEAE is a truly ancient lineage in which beetle pollination is the undisputed pollinator type. Yet, if one simply tallies all insect visitors without considering behavior and floral size and structure, one might come away with a needlessly long list of potential pollinators. Hence, here is a crucial excerpt from a 2014 paper (by Gerhard Gottsberger and Ilse Silberbauer-Gottsbergr) titled "Basal Angiosperms and Beetle Pollination". The excerpt is the entire section titled, "Adaptation of flowers for beetles".All basal angiosperms with bisexual flowers studied in this respect have protogynous anthesis. This is an archaic characteristics in angiosperms and may find an explanation by the early visitors of their flowers flies, thrips and beetles which, contrary to bees, butterflies, birds and mammals, are more stationary at the flowers and often remain on and in an individual flower for a longer time, in some cases for 24 hours or more. In this situation, receptive stigmas at their arrival and pollen-shedding stamens at their departure provides the best and most effective way of pollination.
As the pistillate and staminate stages are often completely separated, an insect-mediated self-pollination is avoided, which is extremely important, because of the high incidence of self-compatibility in the basal angiosperms. Other reasons for this kind of dichogamy may be found in flower construction of basal angiosperms, which have many, densely crowed reproductive organs and stamens lacking long filaments, so that pollen presentation is close to potentially receptive stigmas.
Beetle-pollinated species have the tendency to produce thick, tissue-rich petals, very instructively seen in Winteraceae and others. While the more generalist- or thrips-pollinated species have “normal”, thin petals, the petals of the derived beetle-pollinated Zygogynum species are thick and leathery. This tendency can be seen also in Nymphaeaceae, Calycanthaceae, Magnoliaceae, Eupomatiaceae, Annonaceae and others. The petals are not only thick, but they also curve over the flower center or cover it partly and form a pollination chamber, which is the most important structure to maintain the beetles in their center for the time necessary for the flower to reach the final staminate stage.
The large flowers of cantharophilous species produce strong, enticing odors, whose emission often is intensified by thermogenic processes. Floral scent is mostly produced by the thick petals and heat is produced by metabolization of starch reserves stored in the petals. So petals have several functions, they attract beetles by strong odor emissions, often intensified by flower warming, and the beetles once inside the dark, protecting, warm, energy-saving pollination chamber, find nutritious tissues or food bodies during the pistillate stage of a flower and abundant pollen in the later staminate stage.
Thus A POLLINATION CHAMBER is an ideal place for beetles for hiding, alimenting and mating.
As eating of petals can be destructive, beetle flowers have developed several devices against being destroyed, such as larger flowers with thicker petals, instructively seen in flowers visited by the voracious scarab beetles, or also food bodies on petals, stamens and staminodes, nutritious tissues on the petals, or protective shield-like connectives in Annonaceae.
Flowers can easily “handle” their beetle pollinators. If they provide them a dark, odoriferous, if possible, warm pollination chamber with food then they can keep them as long as necessary to become efficient pollinators! Considering the overwhelming number of beetles, cantharophily especially in mostly tropical basal angiosperms, was the easiest way to become a pollination specialist. Some members of the Nymphaeaceae, some derived Winteraceae, Hydnoraceae, Calycanthaceae, Myristicaceae, Degeneriaceae, Magnoliaceae, Eupomatiaceae and more than 90% of extant Annonaceae elaborated and function on the basis of this efficient and successful beetle pollination syndrome.
Pawpaw Flower Stages
LITERATURE SEARCH: Barlow conducted a literature search, which confirmed that Asimina triloba has not yet had published observations of floral insect visitors that adequately distinguish between casual visitors and effective pollinators. This paper, "Pollination and Evolution in Neotropical Annonaceae", by Gerhard Gottsberger (2008, Plant Species Biology) noted that while this ancient family of tropical flowering plants typically is pollinated by beetles, the flowers of Asimina triloba:"... are of a dark maroon or purple color and exhale an unpleasant odor. Observations, however, are scarce and not well documented... Therefore, it is not yet clear whether this species is in fact pollinated by flies or by beetles, or by both."
Photo by Eric Hunt, Flickr.
ABOVE: The flowers open and become receptive before the leaves are fully extended.
Photo by Connie Barlow, 2021.
ABOVE: Flowers prevent "selfing" by having the female portion of the central reproductive structure (left flower) begin and end its several-day receptive stage before the male (pollen-bearing anthers, right) begin theirs. However, flowers of all stages are present on the same tree, even on the same branch (as evident here), so the issue of self-pollination is still a mystery.
Photo by Dallas Ford.
On May 16, 2021, Connie Barlow and Dallas Ford visited the pawpaw orchard at Marc Boone's farm, southwest of Ann Arbor MI.
Photos and commentary from this visit can be accessed here:
PHOTOS OF SPRING 2021
PHOTO LEFT: Dallas Ford photographed this example of 4 stages of flower maturation all on the same stem:
Green: partly visible at top
Early female: directly below
Late female: left-most
TIMING OF FEMALE & MALE STAGES OF SEXUAL DEVELOPMENT: The definitive paper on the timing of stigma v anther receptivity and ripening also contains many color photos to aid observers with recognizing flower stages: "Pollen-pistil interaction in pawpaw (Asimina triloba), the northernmost species of the mainly tropical family Annonaceae", by Juan M. Losada et al., 2017, American Journal of Botany.
The only paper that deals centrally with pollination problems and effective pollinators of our northern-most Asimina species, pawpaw, was published four decades ago: "Pollinator limitation, fruit production, and floral display in Pawpaw (Asimina triloba)", by Mary F. Willson and Douglas W. Schemske, 1980, Bulletin of the Torrey Botanical Club. Effective pollinators at this study site in central Illinois were not detected for this reason: "Flowers on our study area were rarely visited [by insects]; several extended observation periods yielded no evidence of insect visitation." FLORAL STAGES are, however, well described in this paper, with excerpts as follows:... Pawpaw was most common in old light gaps, some of which had virtually closed. Pawpaw clones extensively and forms such a dense shade that summer understory vegetation is much reduced. We do not know genetic relatedness among the stems we censused but suspect that most stems at a site may be genetically identical.
... Time from opening of the bud and exsertion of the stigma [female tip] from the clump of tightly-packed, closed stamens to petal-drop ranges from 5 days to > 19 days (in a sample of 18 flowers), with most flowers open 15 or 16 days. Petals are green when the flower first opens and gradually redden from pinkish to maroon. The stigma becomes shiny (probably receptive) after 5 to 10 days, remains so for 4 to 6 days, and then turns brown. Pollen usually becomes available when the stigma turns brown, but occasionally earlier. Pollen is available for about 2 days, and sometimes after the petals drop. Flowering times vary between years: in 1977 blooming began in mid-April, 1978 it began in early to mid May. We do not know if such annual differences are accompanied by adjustments of intrafloral phenology.
... There is a clear tendency for flowers on large stems, on high branches, and perhaps exposed to more light, to contain more ovaries.... The sites differed markedly in fruit production, ranging from 1 to 30% of flowering stems with fruit. Furthermore, fruit-bearing stems were not randomly distributed in each site. In two sites, almost all fruit-bearing stems were clumped in areas where the canopy was most open, and each site contained groups of flowering stems that produced no fruit. Despite the fact that flower production was often considerable, with many stems producing > 100 flowers, no stem produced > 4 fruits in 1976. In 1978, fruit production by some large stems reached at least 19. Only 0.41% of the 19,095 flowers censused in 1976 produced fruit.... Fruit production was clearly not associated with the numbers of flowers per site.... Fruiting stems are significantly larger than flowering stem.
... In sharp contrast is the relative success of hand pollinations. In 1978, 804 hand-pollinated flowers produced 135 fruit (17%); in 1977, 78 flowers bore four fruit (5%), and this figure is low because many flowers were not pollinated during the receptive phase. Because abortion of young fruits is rare (< 1%), these results suggest clearly that fruit production by pawpaw at Trelease is pollen-limited.... Pawpaw fruits are green until they are mature and potentially can provide photosynthate for their own growth.
... Flower-visitors are uncommon, which may select for a fairly long floral life and period of female receptivity.
... The fruiting success (and seeds per fruit) of hand-pollinated flowers was much greater than that of open-pollinated flowers and was unaccompanied by fruit abortion. We conclude that at least in our study area, fruit production was pollen-limited, yet it seems certain that a stem could neither mature nor support fruit from all ovaries and flowers produced. The tremendous flower output (up to 500 flowers/stem) may be related to problems of pollen-limitation. Since most flowers do not produce fruit, large floral displays, although perhaps energetically expensive, may increase pollinator visitation rates.
... The great variation in reproductive effort allocated to paternal and maternal functions of flowers is intriguing and worthy of further study. It is not difficult to understand low number of ovaries per flower, especially if local photosynthate is used to support nearby fruits on each branch. We never observed more than four fruits matured per flower on either hand- or naturally pollinated flowers at both Trelease and Mingo. However, the production of 9- and 10-ovaried flowers on some branches is less readily understood, inasmuch as it is virtually inconceivable that all could be matured.
Food for Pollinators
Fleshy Food at Base of Inner Whorl of Petals
ABOVE: This flower in peak female receptivity (2 May 2021, Draper-Houston Preserve) was removed and its petals loosened to reveal the corrugated inner basal area of the set of inner petals. At RIGHT is a single hole apparently bored by some insect through both the outer petal and the inner perhaps to reach the food-rich corrugated part before the flower had opened its petals wide enough to allow entry in the usual way."The inner whorl petals have raised yellow corrugations on their adaxial surfaces, which produce liquid secretions in female- and male-stage flowers." Goodrich et al., 2006, "When Flowers Smell Fermented: The Chemistry and Ontogeny of Yeasty Floral scent in Pawpaw (Asimina triloba)".The scientific literature reports that this fleshy material is taken by insects as a food source:
"The mature flowers have an outer and inner whorl of three, maroon-colored, three-lobed petals (Fig. 7.1). The inner petals are smaller and fleshier, with a nectary band at the base."This statement appears on p 353 of "The North American Pawpaw: Botany and Horticulture", a paper published in 2005 in Horticultural Reviews by a pair of well-known pawpaw horticulturalists: Kirk W. Pomper (Kentucky State University) and Desmond R. Layne (Clemson University). The paper is rich in details for aiding cultivation of this species, so offers little assistance toward understanding wild patches. One sentence simply recounts previous papers pointing to beetles and flies, though mention is also made that "Failure of trees to set fruit could be due to inadequate pollination." More broadly,"The tropical Annonaceae relatives of the pawpaw, such as cherimoya, sweetsop (sugar apple), soursop, and atemoya also have low yields, due to low rates of natural pollination (Peterson 1991; George et al. 1992; Pena et al. 1999). In commercial plantings, these tropical pawpaw relatives are hand pollinated to increase yields (Peterson 1991; Pena et al. 1999). Low rates (<5%) of fruit set have also been noted in wild pawpaw patches (Willson and Schemske 1980; Lagrange and Tramer 1985).
The authors continue, mentioning on p. 371 that CARRION FLIES are possible pollinators but that they, too, are not greatly effective:In the wild, pawpaw trees are usually found in the understory of hardwood forests. Low light levels in the understory likely result in reduced photosynthate partitioning to fruit that may cause low fruit set. Pawpaws in the wild often produce many root suckers that could potentially result in large clonal pawpaw patches contributing to poor fruit set because of self-incompatibility. Pollinator limitation can also cause low fruit set in wild pawpaw patches (Willson and Schemske 1980). Low pollinator activity is usually observed on cool, cloudy spring days. Since the pawpaw flowers are strongly protogynous (Willson and Schemske 1980), lack of pollen availability from other pawpaw genotypes could also limit pollination. Pawpaw growers report that placing carrion in buckets among pawpaw trees has resulted in improvements in fruit set (L. Sibley, pers. comm.) supporting the theory that pawpaw flowers may be pollinated by carrion flies. However, fruit set was 15 to 35% in KSU orchards in 1998 in nine-year-old seedlings where many pawpaw genotypes are in close proximity and flies are abundant due to nearby cattle. Pollinizer relationships between pawpaw cultivars need to be determined. Fruit set can be achieved by hand cross-pollination (Peterson 1997), and needs to be evaluated as a method to increase fruit set."DISPUTING THE CARRION BEETLE HYPOTHESIS: A 2006 paper by Katherine R. Goodrich et al. published in International Journal of Plant Science offers evidence that carrion beetles are not involved in pawpaw pollination. "When Flowers Smell Fermented: The Chemistry and Ontogeny of Yeasty Floral scent in Pawpaw (Asimina triloba)" reported: "We did not detect the dimethyl oligosulfides that characterize the microbial decomposition of meat and universally constitute the odors of carrion-mimicking flowers." Instead, the authors reported a "yeastlike fragrance" in pawpaw flowers. However, "fermentation volatiles were largely absent from female-stage androgynoecia". (Many technical details in this paper may be useful for project participants.)
TESTING THE CARRION BEETLE HYPOTHESIS
LEFT: April 25, 2021, Joe Grant, who lives near the northern-most population of native pawpaw in Michigan, hung out raw meat in an old onion sack, which will become attractive to carrion-loving flies and beetles.
Notice that his pawpaw flowers are well beyond the bud stage, but not yet open. Will the unusual warmth of early April have made these buds vulnerable to the deep frost of late April?
The pawpaw tree shown here is one of about 200 pawpaws planted, with 25 of them mature enough to produce fruit. "Only 5 of our plants are cultivars," he writes.
This is the only participating site that brings carrion into the grove.
QUESTION 1: Will there be insects entering the flowers who do not appear at the other study sites? Will they be effective pollinators?
QUESTION 2: How much overstory shading is at this site?
QUESTION 3: Because there is genetic diversity here, what (if anything) limits pawpaw fruit development?
• SEPT 14, 2021: Report from Joe Grant on fruit production:"We did have 2 deep frosts this year which essentially wiped out the apples but the stone fruit persisted. We had a tremendous pawpaw bloom which lasted an abnormally long time. Thus certain trees are laden with pawpaw and others are barren. Some fruit are ripening 3 weeks early this year due to hot/moist weather. We are getting ready to plant 100 more seedlings."• OCTOBER, 2022: For a second year in a row, Connie Barlow gathered rotting or hard-green fruit from the ground post-season at Marc Boone's pawpaw orchard near Ann Arbor, Michigan. She did this for the purpose of extracting seeds and donating them to planters, preferencing Indigenous groups beyond the bounds of "native" range. While the fruit was abundant this year, much of it did not ripen prior to first frosts. Notably, Marc confirmed that, as usual, he did not place any carrion in the orchard. Pollinators are adequate on their own. Annual differences in fruit abundance seem to be determined by spring weather patterns that are favorable or unfavorable for the timing of budburst.
Pawpaw Pollination: Knowns and Unknowns
Photos by Connie Barlow and Dallas Ford, Washtenaw County (Michigan), Spring 2021
Most of the earlier photos on this webpage had camera angles enabling a view directly into the open flower. However, as shown below, the natural orientation is downward hanging.
Marc Boone Farm, 7 May 2021. A few of the many
pawpaw flower buds had just begun to open.
• Downward-hanging flowers require pollinators to enter from below.
Recall that pawpaw is the northernmost species of a diverse family of tropical fruit-bearing plants: Annonaceae. Perhaps this family developed in a rainforest, where flowers either had to orient downward or develop an ability to open and close quickly. Whatever the history, insects now need to enter from below. This offers a possibility that insects will flip and land either on a petal or on the central stalk of the reproductive organ. The tip of the central stalk is the only location where the female portion of a flower can be pollinated.
Hence, an ideal pollinator is probably one that crawls on its belly along the anthers of a male-stage flower, and thus arrives at a female-stage flower with pollen attached to its underside, legs, or mouthparts not pollen attached to its back (upper side). Ideally, the pollinator alights directly on the tip of the central stalk, and then walks into the interior of the flower to find food.
• Most insect visitors may not be pollinators.
PHOTO LEFT: This fly has pollen visible on its back, where it cannot fertilize the receptive tip of a female receptacle. As well, this pawpaw flower is far past the female receptive stage. The pollen is yellow, whereas pawpaw pollen is white, so this fly must have received pollen from another flower species.
PHOTO BELOW LEFT: The underside of a pawpaw flower may be an attractive place for many types of insects to rest or get out of the rain, without assisting in pollination. Some, as visible here, find the flower a good place to mate.
PHOTO BELOW RIGHT: Clearly, this large beetle was just resting at this peak female-receptive flower.
PHOTOS BELOW: Spiders in flowers at Boone Farm (left) and Draper-Houston (right), May 16. The morning at Boone Farm was cloudy and still, but by the time we got to Draper-Houston early afternoon, it was full sun and very windy. Both locations had spiders in some blossoms, but perhaps half of the blossoms low enough for us to examine at Draper-Houston had evidence of spider webs, and sometimes the spider were visible. Are only soft-bodied flies vulnerable to spiders? What about small, armored beetles, which may be the most effective pollinators?
ABOVE LEFT: May 16 at Draper-Houston showed many blooms on the tall pawpaws. Some deciduous trees had begun to leaf out strongly, especially the Black Willow (tallest in left photo). But in several places the pawpaw stems reached straight up to the sky, with no canopy trees above. Over the years (centuries?) had this pawpaw clone been able to keep growing new stems to the point that the usual floodplain canopy trees could not replace themselves as seedlings or saplings in the darkness beneath a pawpaw patch in peak summer?
ABOVE RIGHT: Pawpaw and walnut seemed ideal companions at Draper-Houston. Because the walnut is the last of the native trees in this habitat to leaf out, pawpaw growing beneath the walnuts had more opportunity to harvest sun late into the spring. Might this cohabitation of valuable human foods have been encouraged by the Indigenous here prior to settler colonization?
ABOVE LEFT: As a subcanopy tree, the stems of pawpaw usually angle in efforts to find and catch sunlight.
ABOVE RIGHT: Wild ginger, Asarum canadense, is a clonal spring-blooming species. It was abundant in some parts within the pawpaw patch and it was flowering on May 16 (photo by Dallas Ford). The flowers were not visible from above. They grew just barely above the ground, facing sideways or even downward, always hidden by the large leaves. The timing, color, (and aroma?) is strikingly similar to pawpaw. Do they share any pollinators? And is Asarum pollinated well enough to produce fruits with seeds? Note: A google scholar search for Asarum pollination reveals that this genus has no conclusive papers on its pollinators either. So the incompleteness of scholarship on pawpaw pollination extends into other species within a wild patch.
Probable Pollinators of Spring 2021
Two small "Sap-feeding beetles" of Family NITIDULIDAE
Photos by Connie Barlow and Dallas Ford, Washtenaw County (Michigan), Spring 2021
ABOVE LEFT: Dallas Ford used a high-resolution camera, excellent for close-ups. But Connie Barlow's hand-held video camera was crucial for filming fast-moving insects from which the best frames could then be converted into stills.
ABOVE RIGHT: At the two young planted pawpaws in Ypsilanti (Maple Street), ants were abundant on the leaves and branches of the trees and also along the rims of the flowers. In contrast, we had not seen ants much, if at all, at either the wild pawpaw patch or the orchard. During 3 very warm afternoons of observations (May 17, 19, 20; which was nearing the end of the flowering time), small beetles were uniquely abundant at the Maple Street site, usually at depth within the flowers. The small beetle visble next to the ant has white showing behind it, which indicates it probably just landed on the petal, as the white are the flying wing tips, usually drawn in and hidden.
TWO NITIDULID BEETLES are the most probable effective pollinators. Both are "Sap-feeding beetles":• Glischrochilus quadrisignatus - "Four-spotted sap beetle" (4 to 7 mm long)This initial speculation of identities of effective pollinators is supported by at least one technical paper. For the Dwarf Pawpaw of southern states, Asimina parviflora, "pollination resulted from visits by nitidulid beetles and rarer calliphorid flies." Richard M.K. Saunders, 2012, "The diversity and evolution of pollination systems in Annonaceae", Botanical Journal of the Linnean Society.
• Stelidota geminata - "Strawberry sap beetle" (3 mm long)
These two genera of "sap feeding beetles" (the species-level ID need expert confirmation) are prime suspects as important pollinators of pawpaw. While we saw very few arthropods, other than spiders, on or in the the pawpaw flowers at Draper-Houston Preserve during a very windy afternoon of May 16, we did observe and photograph one specimen of each, as shown directly below.
ABOVE: Stelidota geminata - "Strawberry sap beetle" (3 mm long). Notice how much tinier it is than the Four-spotted sap beetle, below. Left photo was at Draper-Houston May 16 afternoon, and right photo at Boone Farm the morning of May 16. This is the only insect we documented at all 3 observational sites.
ABOVE: Glischrochilus quadrisignatus - "Four-spotted sap beetle" (4 to 7 mm long). Notice the white pollen grains at its mouth and two specks at rear. (Pawpaw pollen usually aggregates in clumps of four when picked up by a pollinator, so it is big enough to see.) Dallas Ford and Connie Barlow worked together to capture a superb photo of this insect at Boone Farm on May 16. We saw many more of this species at the Maple St. site in Ypsilanti, but this photo was the clearest for identification.
The above 2 beetle types are prime suspects as important pollinators of pawpaw in Michigan because we documented them in about 80% of the blossoms during the peak insect day (May 19) at the Maple Street site and because in early July, we recorded fruit at the Maple Street site so pollination was achieved by some insect visitor.
On May 19, the small beetle was far more abundant. On May 20, the big beetle type was slightly more abundant.
CAVEAT: Because the Ypsilanti site was the final watch site in May, only here did we discover (and then faithfully apply) a crucial technique for observing pollinators: After first gently turning the flower upward and looking for insects, we placed a bowl directly beneath and tapped the stem. It was rare to observe any of these small beetles except when they fell into the bowl, as they were deep in the flower, often hidden by anthers.
Maximal count shaken into the bowl from within a single flower was 4 bigger beetles plus 2 of the smallest.
ABOVE: Early July 2021, we counted 7 pawpaws growing on the bigger tree at Maple Street (left) and one doublet at the smaller tree (right).
• NOTE ON FLOWER AROMA: The yeasty smell of pawpaw blossoms during Maple Street 2021 observation seemed to be strongest in peak female stage flowers, but also carrying strongly into male pollen stages. There was no discernible aroma in green flowers or very early purplish female flowers that were still rather closed and appeared to have only a faint glistening on female tips (day 1?). A technical paper on pawpaw aroma is "When Flowers Smell Fermented: The Chemistry and Ontogeny of Yeasty Floral Scent in Pawpaw, Asimina triloba", 2006, by Goodrich et al., International Journal of Plant Science. Key excerpts:
"Sexually mature flowers emitted fermentation volatiles, with additional nitrogenous compounds (androgynoecium) and butanediols (outer corolla) emitted by male flowers. Some compounds were detected only when scent was sampled from at least 10 flowers. Chemical composition was more complex during day than night for immature and female flowers but not for males. Emission rates were fourfold greater in male than female flowers during the day but were comparable at night, perhaps because of overlapping gender expression. The yeasty odor of A. triloba is unusual in angiosperms and may serve to attract novel fly and beetle pollinators."• Crucially, Glischrochilus quadrisignatus (as well as Glischrochilus fasciatus) has been documented as responding to yeast aromas. Reference: Lin and Phelan, 1991, "Identification of Food Volatiles Attracive to Glischrochilus quadrisignatus and Glischrochilus fasciatus".
* * * * *
ADDITIONAL PHOTOS OF BEETLES AT MAPLE STREET residential pawpaw cultivars in Ypsilanti
during 3-hour observation sessions the afternoons of May 17, 19, and 20.
Calm and uncomfortably warm days.
ABOVE: The biggest beetle type (Glischrochilus) is left; smallest (Stelidota) is right.
ABOVE: Beetles preparing to fly (left is big species; right is small).
CLOSEUP OF THE BIGGEST SPECIES:Because Connie had a video camera, she was able to extract the best frame when the largest of the 2 beetle species prepared to take flight.
"Four-spotted sap beetle"
These photos were taken in sunlight, so they are the best for observing the orangish markings on the beetle. The white strands and dots would be pollen which might have accumulated on beetles while they were shaken into the bowl.
• BEETLES USUALLY CANNOT BE SEEN IN THE FLOWER UNTIL SHAKEN OUT:
The observational technique pioneered at the Maple St. site was to gently turn a flower upward and peer into the flower with a magnifying glass. Then we let the blossom return to its downward orientation, while holding a white cereal bowl close to its underside. Then we tapped the stem to shake out some or all insects. Read the "Pawpaw as an Ancient Flower Type" section to learn WHY EFFECTIVE POLLINATORS SPEND A LONG TIME INSIDE THE FLOWERS.
It seemed that both beetle types would fall into the bowl. Rarely did one take flight while falling, and then it was only the bigger beetle type that flew. Once in the bowl the bigger type sometimes remained for less than the time it took us to capture a photo or video. The small beetle type almost always just crawled around the bowl for several minutes before departing. If beetles didn't depart, we carried the bowl back to the pawpaw and tipped the bowl upside down over a section of flowers, as these beetles are notoriously weak fliers.
ABOVE: The bigger beetle is shown here "playing dead" after falling out of a late-stage male flower. Vigorous shaking of the flower over the bowl prompted many of the spent anthers to fall out too. Because the shaking was vigorous, pollen on the beetle may have happened during shaking.
BELOW: However, as with previous days, the beetles tend to have a lot of pollen around their mouths. But perhaps they used their mouthparts to grip anthers when the shaking started.
• Photos and commentary from all spring 2021 pawpaw observations can be accessed here:
PHOTOS OF SPRING 2021 pollinator surveillance
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• 2022 UPDATE: A new potential pollinator at the Ypsilanti horticultural site
In 2022, Connie Barlow was asked to hand-pollinate the flowers of the two horticulture pawpaw trees at the same Ypsilanti neighbor's home on Maple Street, as shown in the 2021 beetle photos above. Below are two photos of the same beetle apparently the same size as the Glischrochilus found in the flowers in May 2021. The protruding mouth part is an obvious difference.
COMMENTARY BY CONNIE BARLOW: Because I was asked to perform hand pollination of the flowers, I did not search for pollinators lurking at depth in the flowers (which are usually visible only with vigorous shaking or by dislodging petals). Nevertheless, in the process of acquiring pollen from the male-stage flowers on one tree for rubbing on female-stage flowers on the other, I did encounter one beetle. The photos above of this as-yet unidentified beetle show it to be about the same size as the Glischrochilus beetle.• 2023 UPDATE: A resident of Lansing, Michigan, posted a comment on our youtube video, "Citizen Science discovers Pawpaw Pollinators in Michigan" on her own pollinator observations:
HAND POLLINATION AMPLIFIED FRUITING. Year 2021 produced less than a dozen fruits, while year 2022 produced 38. May 19 was when I hand-pollinated the flowers in 2022, compared with May 17-21 pollinator observation in 2021. In addition to fruit numbers, there are two other observations that suggest hand-pollination greatly amplified fruit production: (1) In 2022 there were no fruit above the height I could have reached while pollinating the flowers. (2) In contrast to the singles, doubles, and rare triplet fruits of 2021, there were abundant triplets, several quads, and even one 5-fold fruit in 2022. A contrary hypothesis could be that, in 2021, the act of severe shaking of flowers to dislodge tiny beetles hidden at depth may have in itself caused harm to flower parts or disrupted insect behavior such that it was the observational process itself that reduced successful flower pollination."I've got a number of paw-paw trees on my suburban lot in Okemos, 5 of which produce flowers (the others are still too young). I used to hand pollinate, but for the last 4 years, I've not needed to. I was pretty sure it was some tiny flies and those beetles with the spots that were my pollinators but have never been so methodical about finding out. This is great work. Thank you and congratulations!"When asked about her observational technique, she replied that when hand-pollinating she used a small paint brush to gather pollen. "When I gather the pollen, inevitably, the beetles fall out, too."
• 2023 UPDATE: June 2023 Facebook post shows tiny flies on pawpaw flower:
BARLOW can't track who posted this on Facebook:
"This Pawpaw flower has many tiny flies swarming it at home in town. The place where I have the Hawthorn planted has well over 10,000 pawpaw stems in that woodland and field edges and I have tremendous pollination resulting in fruit on pawpaws. Could these be the little midges that you were speaking of that would help pollinate the hawthorn? I have noticed these same insects out in the country on those paw paw flowers.
FB RESPONSE: They very well could be. Midge is a catch-all noun for very small two winged true flies, often with a body no larger than the head of a pin. Many can look like mosquitoes and gnats. If your hawthorn decides to flower and you end up with a good amount of fruit, then you can probably thank your pawpaw flies. It's truly incredible how nature interacts to get things done; very humbling!"
South African Cycad Paper Distinguishes Casual Visitors
from Effective Pollinators
• "Beetle Pollination of the Fruit-Scented Cones of the South African Cycad, Stangeria eriopus", by Servan Proches and Steven D. Johnson, 2009, American Journal of Botany.COMMENTARY BY CONNIE BARLOW, April 2022: I have been continuing a scholarly paper search for help in discerning casual from effective potential pollinators, given our 2021 initial observations onsite of insects on and especially deeply within pawpaw blossoms. The above cycad paper (which concludes SAP BEETLES as the effective pollinators) is the only paper thus far that offers:(a) the possibility that the female receptive stage attracts pollinators via DECEPTION (scent of a food source, but after landing on the moist receptive stigmata at the receptacle tip, the insects may or may not leave), or that TINY SAP BEETLES, after landing on the female tip, are small enough to then crawl downward along the receptacle, seeking food and/or possibly a site for safety, warmth, and eventually mating.Notably, this cycad paper listed both SAP BEETLES and FRUIT FLIES as common insect visitors, but concluded (via the dye experiments) that "only sap beetles (Nitidulidae) were able to effect pollination under experimental conditions.":
(b) that there is indeed a method for determining pollen deposition on receptive stigma (using a dye) but THIS METHOD DOES NOT APPEAR TO HAVE EVER BEEN USED FOR GENUS ASIMINA.... "Our scent analyses, observations, pollen load analyses, and ex situ dye transfer experiments strongly suggest that small-bodied insects, specifically sap beetles (Coleoptera: Nitidulidae) are the main pollinators of Stangeria.... When fruit flies and other beetles were tested, fluorescent dye was recovered on the outside of the cone scales, but not on ovules or micropyles.... Our ex situ experiments showed that, of all insects commonly encountered on the cones, only sap beetles were efficient vectors of pollen to the micropyles. Sap beetles could indeed account for much of the seed set observed in cultivated Stangeria plants throughout the world. Sap beetles are a cosmopolitan family, and in fact all three species used in our ex situ experiments are widespread pests of dried fruit.Note: Barlow learned of the above paper owing to its reference in "Pollination systems involving floral mimicry of fruit: Aspects of their ecology and evolution", by Katherine R. Goodrich and Andreas Jurgens, 2017, New Phytologist.
... REWARDS: As is the case for Encephalartos (Donaldson, 1997), we assume that female cones of Stangeria offer no rewards and are visited entirely by mistake. This deception is facilitated by the very closely matched chemical composition of male and female cones (Fig. 7), that presumably makes it impossible for beetles to discriminate among the sexes. That pollen was found on beetles' mouthparts and was accepted by captive beetles indicate that the beetles do indeed feed to some extent on pollen in the male cones, but analysis of feces suggests that pollen is not their main food source in the wild. The male cones of Stangeria also do not appear to be damaged by insect feeding in the wild, unlike the brood site mutualism in Encephalartos in which weevil pollinators consume most of the fleshy tissue in male cones (Donaldson, 1997).
Ecological Interpretations of 2021 Field Experience
offered by CONNIE BARLOW
The papers listed, linked, and excerpted in the section that follows this were read by CONNIE BARLOW, in quest of ascertaining the environmental conditions, habitats, and plant associates that support adequate populations of the PAWPAW POLLINATING INSECTS.
• DERIVED HYPOTHESES OF ECOLOGICAL INTERACTIONS:1. Overall, it is possible that domestic and wild pawpaw groves may benefit from nearby cornfields and/or mature forests with rotting wood to support (a) below-ground overwintering adults and possibly also (b) beetle larval food which prior to agriculture might primarily have been fungal mats in rotting logs.• EXPLORING THE NITULIDID BEETLE CONNECTION WITH OAK WILT DISEASE:
2. Owing to unharvested strawberry and cherry fruit crops becoming artificially super-abundant foods for adult pollinating beetles (and also larvae?), it is pest-control and applied entomology journals that provide some of the best literature for learning the natural history of potential pawpaw pollinators that are nitulidid beetles (Glischrochilus and Stelidota), as seems likely from the Spring 2021 pawpaw flower observations.
3. If the above hypotheses are correct in the main, then Marc Boone's pawpaw orchard likely benefits from nearby cornfields and the adjacent mature woodlots. Overwintering adult beetles might also benefit from woodchips initially placed around each pawpaw tree and perhaps could benefit from a fresh layer of woodchips. And the fact that Boone's U-Pick orchard accumulates rotting pawpaw fruit beneath the trees (that is not removed) may also provide an important late-season larval food source, with emerging adult beetles simply burrowing down through the wood chips to spend the winter.As a consumer of fungal mats, as well as the yeast-smelling petal tissues evolved by pawpaw to entice pollinators, both Glischrochilus and Stelidota are implicated as carriers of oak-wilt-disease-causing fungal spores on their bodies when visiting sap-yielding injuries on Red Oak species, especially during the spring. It is possible, however, that oak wilt disease has become a problem largely in the vicinity of agricultural-scale cornfields. Such cornfields may facilitate late-summer, super-abundant populations of these nitulidid beetles. (See the papers below on corn as larval food and in-field corn cobs on the ground as overwintering habitat for adult beetles.) Thus cornfields may introduce a boom-and-bust annual population cycle. If the overwintering beetles are in fact super-abundant, their spring emergence would have them stressed to find naturally occurring wild food sources (such a pawpaw petals). This may contribute to their wider dispersal and thus their attraction to sap-yielding injured stems and branches of species of RED OAK trees especially if there are two generations of beetles produced during Michigan summers, rather than only one.• UNIQUE ECOLOGICAL CHARACTERISTICS OF THE WILD PATCH AT DRAPER-HOUSTON PRESERVE:
Overall, it would be useful to assess whether oak wilt disease is largely a problem of patchy farm-woodlot areas not large-scale, wild forests. Both nitulidid beetle species are known to be poor fliers and thus do not disperse widely. As well, because the wild patches of pawpaw in Michigan tend to be found in floodplain forests that favor trees other than the red oaks (notably, Swamp White Oak, Hackberry, Black Ash, Black Willow, Black Walnut, Basswood, Cottonwood, Sycamore), it is possible that, whether the oak wilt fungus is native or introduced, the disease effects would not have generated concern for red oak species were it not for the abundance of woodlot-cornfield patchiness.1. Owing to the temperature modulating effects of the Saline River, it is possible that fewer flowers at the preserve succumbed to deep frost (than had happened at Marc Boone's orchard and Joe Grant's orchard) because the unseasonably warm spell in April would have had less effect along the Saline River in fooling the flower buds into losing their winter resistance. Connie did notice some crisp flowers (indicative of prior frost damage) that had fallen in the Draper-Houston pawpaw patch during an extremely windy, sunny afternoon visit on May 1. But given that there is no prior documentation of fruiting in the wild patch, we have no prior year results for comparison.(and the reading she had done on the ecology of that subcanopy native tree). Perhaps just like has been documented with Pacific yew, pawpaw may become a "climax dominant" if its habitat is undisturbed over the course of centuries. Both yew and pawpaw are capable of growing beneath a canopy of taller trees. And both have extremely long-lived roots with far-reaching subsurface horizontal rhizomes (ramets) that generate expanding clones with no additional seeding necessary. Thus, when an overstory species stem dies or falls, a pawpaw clone grows prolifically in the sudden increment of full sun. If an overstory species sends a seed into that site again, the germinated seedling cannot survive in the dense shade of the pawpaw's own low canopy. Indeed, as Connie reflects back on her visits, the remarkable section of pawpaw that had no overstory shade blocking it probably arose by exactly this process. And the only tall overstory stems remaining "in" the patch were pretty much edging the bare muddy rounds of ephemeral pools. A seedling of an overstory species that happens to germinate right along the pool edge finds dependable sunlight along one side for the years it takes to top out above 30-foot-tall pawpaw trees. If this combination of natural history observation and ecological reasoning is actually true, then what we experience at the wild patch along the Saline River may well be old growth forest of a climax-dominant subcanopy species. In this way, the wild patch may be no less worthy of our awe and respect than any of the easier to recognize old growth characteristics of a set of overstory tree species.
2. Only after her fifth visit to the wild patch did Connie begin to recognize a similarity of that patch to her experience with Pacific Yew
for Ascertaining Ecological Interpretations
of the Spring 2021 Evidence
excerpted by CONNIE BARLOW
• "Sap beetles hitting Michigan cherries", 18 May 2020, Matt Milkovich, GoodFruit Grower.
LEFT: A picnic beetle (Glischrochilus quadrisignatus), seen here, is one of the common sap beetles found in Michigan. Sap beetles did more damage than usual to cherries in Northwest Michigan in 2019. Michigan State University researchers are studying the problem.
AS PESTS: Sap beetles are typically secondary pests of sweet and tart cherries in Northwest Michigan, but populations seem to build up to commercially damaging levels following seasons in which lots of unsold fruit is left around to rot. Those ideal conditions for the pest were reached in 2010 and again in 2019, when processors started rejecting fruit. "We usually don't have issues with sap beetle," said Nikki Rothwell, coordinator of Michigan State University's Northwest Michigan Horticulture Research Center. "It's not something we spray for regularly."
Processors started calling the research center during the 2019 harvest, saying they were finding larvae in their cherries. At first, Rothwell assumed it was spotted wing drosophila (SWD), but when her team looked closer they discovered it was the much larger larvae of the sap beetle, she said during the 2020 Northwest Michigan Orchard and Vineyard Show near Traverse City in January.In response to this unexpected infestation, the MSU researchers decided to take a more detailed look at sap beetle characteristics. Their findings are still preliminary, but Rothwell said beetle populations, attracted to cracked and rotting fruit, likely are driven by cherries left on trees and on the ground. And because of SWD infestation, growers dumped more cherries on the ground in 2018, which might explain the greater sap beetle problem the following year. SWD is doing more and more damage to cherries in Northwest Michigan, leaving more and more fruit to rot. Because of this, Rothwell is concerned that sap beetle populations might build up over time. She said more data is needed on the relationship she hypothesized between SWD and sap beetle.• "Sap beetles (Coleoptera: Nitidulidae) in managed and old-growth forests in southeastern Ontario, Canada, 2006, by Rebecca Zeran et al., Canadian Entomologist.
Michigan has two main species of sap beetle: the picnic beetle (Glischrochilus quadrisignatus), about a quarter of an inch long; and the strawberry sap beetle (Stelidota geminata), an eighth of an inch long. Both species have little knobs on the ends of their antennae and both have been found in Northwest Michigan cherries, Rothwell said. The larvae have six legs and are much larger than SWD larvae. They also have straight bodies and a distinct head capsule, she said.
Sap beetle is a more common pest in other crops, including sweet corn and raspberries, but especially strawberries. The beetles frequently fly into fields from wooded areas nearby. Attracted to rotting fruit, they usually show up after picking, when berries are left on the ground. Both adults and larvae feed on fruit, doing two types of damage from direct feeding, which leaves a distinctive hole in a rotting berry; and indirectly by spreading rot pathogens, Rothwell said. MSU recommends strawberry growers immediately remove damaged, diseased and overripe fruit from the field, or at least cover it, to keep beetles out. As for insecticides, Brigade (bifenthrin), Danitol (fenpropathrin), and Assail (acetamiprid) can provide some control in strawberries, but it's not guaranteed. Their efficacy has not yet been tested in cherries, she said.NATURAL HISTORY: There were three peaks in the abundance of G. quadrisignatus over the season: in May, late July, and mid-September (Fig. 2). This pattern is similar to that observed by Dowd and Nelsen (1994) and suggests that G. quadrisignatus might have two generations per year. However, Luckman (1963) concluded that there was only one generation per year, proposing that the emergence of overwintering adults accounts for the spring peak, while their larvae, which develop throughout summer and then pupate and emerge as new adults, account for the mid-July peak. Our late-season peak may represent local movement of the same generation, driven by the availability of maturing corn late in summer.• "Identification of Food Volatiles Attractive to Glischrochilus quadrisignatus and Glischrochilus fasciatus, 1991, by Hengchen Lin and P. Larry Phelan, Journal of Chemical Ecology
... The presence of large numbers of G. quadrisignatus at two of the six stands can probably be explained by the attraction of this species to maize crops (Luckman 1963; Blackmer and Phelan 1995). The stands in which this species was most abundant were the only ones surrounded by active corn fields; these fields likely attracted the beetles to the area, increasing their abundance in adjacent forest stands. However, it is difficult to justify removing this species from the analyses entirely, because it probably undergoes larval development and adult overwintering in the forest (Luckman 1963), making it a significant component of the nitidulid assemblage in those stands, with obvious interactions with and potential effects on other species.... Results including G. quadrisignatus suggested that forest management has a negative impact on the species diversity of Nitidulidae.MATURAL HISTORY: In this study, we sought to elucidate chemicals mediating food finding in Glischrochilus quadrisignatus and G. fasciatus to allow a broader interspecific comparison of this process among members of this group of insect herbivores.... Odor baits: Although a variety of fruits and vegetables were attractive to Glischrochilus quadrisignatus and G. fasciatus, whole wheat bread dough was one of the most attractive substrates.... Yeast-inoculated banana, another attractive substrate, was tested in the first trial to confirm that bread dough and yeast-inoculated banana were equally effective in attracting these beetles.... In attracting Glischrochilus species, ethanol is an essential component and its activity is not replaceable with any other bread dough odor components.... Aim et al. (1985) also found the difference of these two species in response to volatile chemicals in the field: G. quadrisignatus was attracted to butyl acetate, and G. fasciatus was not, although both species were attracted to natural substrates....• "Ecological analyses of Nitidulidae: seasonal occurrence, host choice and habitat preference", 1995, J.L. Blackmer and P.L. Phelan, Journal of Applied Entomology.
AS PESTS: ... Glischrochilus quadrisignatus (Say) and G. fasciatus (Olivier) are insect pests of many small fruits and vegetables. Severe damage to corn, strawberry, cane berry, and tomato caused by Glischrochilus species throughout the continental United States and Southern Canada frequently have been reported (Pree, 1969; Foott and Hybsky, 1976; Miller and Williams, 1981). In addition, nitidulid beetles are considered the primary vectors of oak wilt disease (Appel et al., 1986), and G. quadrisignatus and G. fasciatus are among the principal insect species associated with oak wilt-infected trees (Dorsey and Leach, 1956; Juzwik and French, 1983). G. quadrisignatus is also associated with Fusarium pathogens of corn roots, stalks, and ears (Windels et al., 1976), and is capable of transmitting conidia and ascospores of Gibberella zea (the perithelial state of Fusarium graminearum) causing rot to corn ears (Attwater and Busch 1983). Furthermore, Glischrochilus species can be a considerable nuisance by disrupting picnics and other outdoor activities (Luckmann, 1963; Miller and Williams, 1981).NATURAL HISTORY: .. The Nitidulidae represent a diverse family of insects, especially in tropical regions. These beetles feed on a variety of substrates including decaying fruits and vegetables, fungal mats, carrion, pollen and flowers. A dichotomy in feeding habits exists within the Nitidulidae: Cateretinae and Meligethinae feed and breed in flowers while Carpophilinae, Cryptarchinae and Nitidulinae feed on fungi and decaying organic matter. The primitive feeding habit is believed to be the association with decaying organic matter, wood and wood fungi, with more derived nitidulid species being associated with flowers and pollen.• "Nitiullidae (Coleoptera) Diversity in Three Natural Preserves in Portage County, Ohio", 1992, Roger N. Williams et al., Ohio Journal of Science
... G. quadrisignatus occurred almost exclusively in agricultural settings, whereas G. fasciatus occurred predominantly in woodlots. Numbers of S. geminata fluctuated seasonally, showing a preference for woodlots early and late in the season and a preference for agricultural settings throughout most of the summer. Although the Nitidulidae have had a longer association with climax communities than with ruderal [agricultural] communities, the diversity of nitidulid beetles was similar in the two habitat types. This may be because many of the resources these beetles use for food and oviposition sites in climax communities are ephemeral and closely related to the resources that they use in ruderal communities (i.e. wild versus domesticated strawberries, wild versus domesticated cherries and hawthorn fruit versus apple).
... Although we found G. quadrisignatus adults feeding on fruit and vegetables throughout the summer and autumn, larvae were found only in the spring and only on maize ears that had been plowed under in the previous year's harvest.... For another species, Stelidota octomaculata, we proposed that the apparent discrepancy between the beetles' broad olfactory response in the laboratory and its narrow host range in nature might be explained by its low dispersal capability, which could lead to ecological isolation.NATURAL HISTORY: ... Baits included: whole wheat bread dough, fermenting brown sugar, cantaloupe, carrion, and banana. Most frequently collected nitidulid species were Stelidota getninata (Say), Glischrochilus quadrisignatus (Say), G. fasciatus (Olivier), and Carpophilus lugubris Murray.... Carrion as bait was incorporated into this study in order to attract a single group of sap beetle in the genus Nitidula. According to Dr. Walter A. Connell (pers. comm.), no more than a few Nitidula specimens have ever been collected at a single host and those usually from animals that are completely decomposed with only the bones and hide remaining. Carrion was ranked fifth when considering total number of specimens collected. However, Omosita colon was the only sap beetle caught.• "Evaluation of flight phenology and number of generations of the four-spotted sap beetle, Glischrochilus quadrisignatus in Europe", 2012, Sandor Keszthelyi, Bulletin of Insectology.
AS PESTS: Stelidota geminata was the most abundant sap beetle captured in the present study, and also one of the most damaging to the strawberry crop in eastern North America. It damages approximately 10% of the all strawberriesgrown in Ohio (Weiss and Williams 1978).The picnic beetles, Glischrochilus quadrisignatus and G.fasciatus are not only pests of fruit crops, contaminants of fruits and vegetables, vectors of plant disease, and nuisance pests at picnics, athletic events, and outdoor weddings (Borror et al. 1989, Parsons 1943), but also play a rather important role as beneficial insects. They have been used in integrated pest management programs to assist in the control of the European corn borer (Luckmann 1963). The picnic beetles enter the holes made by the European corn borer and kill the invading borer larvae.NATURAL HISTORY: The four-spotted sap beetle, Glischrochilus quadrisig- natus (Say) is a native species in North and Central America. Its endemic distribution area is Nearctic and Neotropic regions of American Continent (Parsons, 1943). Its European invasion began with introductions via transports of fruits and vegetables for American army in Europe at the end of World War II. The first dated confirmation of its presence in Germany was from 1948 (Karnkowski, 2001). Since then the range of its invasion has extended to other countries of Central and North Europe, Balkan Peninsula, Apennine Peninsula and western Russia (Audisio, 1985; Kałmuk et al., 2008).• "Sap Beetles (Coleoptera: Nitidulidae) in Oak Forests of Two Northeastern States: A Comparison of Trapping Methods and Monitoring for Phoretic Fungi", 2020, Marc F. DiGirolomo et al., Journal of Economic Entomology
... G. quadrisignatus develops several generations as a function of its distribution area (Luckmann, 1963). So it may have one (Funt et al., 2004), two and even more generations per year. ... G. quadrisignatus overwinters as an adult and becomes active on warm days in late winter or early spring. Most eggs are deposited in May. Females can oviposit up to 400 eggs in their lifetime. To be suitable for oviposition and larval development, food material must either be buried in the soil or be in contact with the soil and must be moist. Active adults of the new generation begin leaving the soil in June. They fly to fields of ripening or damaged berries, tree wounds, and maize. Adults live long time (40-60 days), and late in June various life stages including both the new and overwintering generation can be found together in the soil (Blackmer and Phelan, 1995).... The numerous trapped individuals in maize monoculture can be explained with its overwintering site, because the maize ears found in the soil as G. quadrisignatus food can give shelter to the overwintering adults (Blackmer and Phelan, 1995; Luckmann, 1963). So its overwintering is more successful.AS VECTORS OF OAK WILT: Oak wilt, a disease caused by the fungal pathogen Bretziella fagacearum, was first detected in the northeastern United States in 2008 (Jensen-Tracy et al. 2009) and threatens the health of native oak forests. Oak wilt has two principal modes of transmission: local, underground spread by way of root grafting, and longer distance, overland spread by insect vectors (Gibbs and French 1980). Sap beetles (Coleoptera: Nitidulidae) are considered an important insect group in pathogen transmission (Dorsey and Leach 1956, Juzwik et al. 2004, Hayslett et al. 2008). Some sap beetles, as their common name implies, are attracted to and feed on sap created by wounds on trees. However, the feeding habits of nitidulids are diverse and include seeds, pollen, flower petals, beeswax and honey, carrion, and predatory on other invertebrates, with a majority living in decaying fruits, fermenting plant juices, and fungi (Parsons 1943). Oak wilt produces sporulating mats on the outer sapwood and inner phloem of infected trees (Gibbs and French 1980), which emit a volatile odor that attracts nitidulids (Lin and Phelan 1992). Beetles propagate the disease by then carrying spores from these mats to fresh wounds in otherwise healthy trees (Juzwik et al. 2004).... This study explores the diversity of spring flying nitidulid beetles and associated fungi isolated from them in the northeastern United States, while evaluating the efficacy of different types of traps.
Glischrochilus fasciatus and Glischrochilus vittatus (Say) have been reported as predaceous on the bark beetles, Trypodendron lineatum (Olivier) and Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), respectively (Chamberlin 1918, 1939), and Glischrochilus spp. are known scolytine predators in Europe (Parsons 1943).
RECOMMENDATIONS FOR ORCHARD HABITAT MANAGEMENT
• POLLINATOR CONCLUSIONS (as of April 2022): SAP-BEETLES (Nitidulidae) are the most likely and abundant effective pollinators. Spring 2021 pollinator survey by Connie Barlow and Dallas Ford confirmed abundance (and extended deep flower habitation mating?) of Glischrochilus quadrisignatus and the even tinier Stelidota geminata:
• HABITAT MANAGEMENT RECOMMENDATIONS (as of April 2022):
MARC BOONE'S CURRENT HABITAT MANAGEMENT likely offers ideal conditions for LIFECYCLE SUCCESS of the beetles. The most important element for full life-cycle success may be Boone's practice of allowing post-season fruits to remain where they drop beneath the pawpaw trees, as eggs are laid by the beetles in rotting fruit. There the larvae feed, pupate, and emerge as beetles in time to burrow into the ground (as deep as 15 cm) before winter freeze. Possibly his practice of putting wood chips beneath the trees ensures undisturbed and insulated winter habitat. Nearby woodlots and agricultural fields may or may not play important roles during pollinator lifecyles after the bloom time and onward through the summer.
ABOVE LEFT: Collecting remaining pawpaw (and a few orange persimmon) fruits 8 November 2021 weeks after the end of the U-Pick season at Marc Boone's orchard. The container with the orange persimmons has a pile of rotten fruit at its other end.
ABOVE RIGHT: Connie Barlow separates seeds from the rotten pawpaw fruits 14 November 2021. The process (and background information) is recorded in video format and published on youtube as "Helping Forests Walk 04: Helping Subcanopy Trees Migrate" (50 minutes).
ABOVE: This four-spotted sap beetle, a dominant pollinator of pawpaw flowers, is photo-documented here emerging from rotten pawpaw fruit that Connie was extracting seeds from mid October 2022. A close look at some of the rotting flesh on the inner side of pawpaw skin reveals larvae of different ages.
ABOVE LEFT: Scale view of the beetle larvae.
ABOVE RIGHT: Discovery of adult 4-spotted sap beetle among rotting grapes from a cluster of a neighbor's vine, mid August 2023. (Connie returned the beetle with a few rotting grapes to the soil beneath the grapevine in order to ensure pollinator reproduction for the pawppaw trees 2 doors down.)
• REMAINING QUESTIONS: Given that pawpaw fruit begin to ripen in September, and that no insects seem to utilize the developing fruit for egg-laying and larval development, what do the adult beetles do post-flowering and during the summer?• What plants do the beetles eat during the summer, and where does the pollinating generation of nitidulid beetles deposit their eggs?Specifically, what rotting fruits are available in Michigan in spring or early summer? Could wild strawberries have been the co-evolved food source for Stelidota beetle larvae? Then, possibly wild raspberries. As for the larger Glischrochilus, it is now well established as using rotting corn cobs for oviposition and for overwintering as adult beetles as deep as 15 cm into the farm soil. Does this beetle also find good egg-laying habitat in the fallen orchard apples that continue rotting in the spring? (Advance to the "Habitat management" section for more information and references.)
GERMINATION & WILD PLANTING EXPERIMENTSIMPORTANT DISCOVERIES: After digging up the seeds from winter stratification, I put some in the refrigerator and removed them at monthly intervals to watch for germination success and timing. Overall, I learned:
Summer of 2023
• Germination can be delayed by refrigeration, without reducing germination success.
• Seeds put into room temperature soil conditions will begin to germinate in about 7 days at the earliest. All viable seeds will have germinated within just 4 weeks. I kept some ungerminated seeds continuing in the kitchen for the whole summer, and just 1 germinated after 2 months.
ABOVE LEFT: Rarely, a seed that did not germinate felt squeezable. I opened one and found worms of some type inside.
ABOVE RIGHT: I laid the seeds horizontally on top of soil in several containers in the kitchen, covered them with paper towel, and kept the top moist. This way I could see germination without having to dig. And that is why in this photo the roots all orient in the same way.
Summer of 2023, I decided to germinate some pawpaw seeds indoors (left).
Four germinated seeds I planted into a bucket (below), so that later I could see how their roots developed, before planting them out on family property to perhaps become an orchard.
FURTHER QUESTIONS AND SUGGESTIONS FOR EXPERIMENTS• REMAINING QUESTIONS FOR BEST PRACTICES (as of April 2022): Given that pawpaw fruit begin to ripen in September, but the beetles do not oviposit prior to the onset of fermentation, what do the adult beetles do post-flowering and during the summer? When and where does the pollinating generation of nitidulid beetles deposit eggs? What rotting fruits are available in spring or early summer?
A 1995 paper, Ecological analyses of Nitidulidae: Seasonal occurrence, host choice and habitat preference", by J.L. Blackmer and P.L. Phelan (entomologist at Ohio State U), in Journal of Applied Entomology, concludes that overripe wild strawberries may have been a co-evolved spring food source for Stelidota beetle larvae. Then, possibly wild raspberries. As for the larger Glischrochilus, it is now well established as using rotting corn cobs for oviposition and for overwintering as deep as 15 cm into the farm soil. (See "Glischrochilus quadrisignatus, Coleoptera, Nitidulidae".) Does this beetle also find good egg-laying habitat in spring rotting of the overwintering wild hawthorn fruits, and now increased by the fallen orchard apples that continue rotting in the spring?
This webpage provides information on Glischrochilus quadrisignatus from the standpoint of farmers viewing the beetles as pests on over-ripe fruit:Host Plants. The adults feed principally on damaged or decaying vegetables and fruits such as cantaloupe, sweet corn, tomato, apple, peach, and pear, and also on fungi. Late-season adults also attack ripe but undamaged fruits and vegetables, particularly corn and raspberry. Sometimes they also have been known to attack onion sets, potato, and strawberry.
Life Cycle and Description. This beetle overwinters in the adult stage. Oviposition occurs early in the spring, and in Ontario larval development is completed in May or mid-June, with new adults appearing in July and August. This pattern is similar in such midwestern states as Minnesota, Iowa, and Illinois. Although only a single generation occurs annually in most of the northern regions, apparently a second generation occurs in Illinois (Dowd and Nelson, 1994), and a few insects go on to produce a second generation even as far north as southern Ontario (Foott and Timmins, 1977). The eggs are deposited in the spring, principally on decomposing ears of corn, though they also occur in the soil near food. Other oviposition sites include decaying cabbage, onions, and potato-seed pieces. Beetles dig in the soil to a depth of 15 cm to seek a suitable oviposition site. Females can produce about 300 eggs, which are deposited singly or in small clusters. Pupation usually occurs within a small cell in the soil in the immediate vicinity of the larval food source. The pupa initially is white, and turns tan before adult emergence. Duration of the pupal stage is usually 8-12 days, and then the adult remains below-ground for about 12 days before digging to the surface. Adults overwinter in clumps of grass, under rotting fruit and vegetables and under leaf mold and bark, but especially in the top 2.5 cm of soil. Areas with grass sod and tall weeds are preferred relative to areas with sparse vegetation or forest. Many of the females overwintering are already mated. Adults that emerge in the summer initially are tan rather than black. Adults are long lived, and at mid-summer both new adults and adults from the previous summer can be found. Food lures: Attractants such as banana, sweet corn, and whole wheat-bread dough are most effective. The chemical components of many fruits—butyl acetate and propyl propionate—also are effective lures.
PRACTICAL OUTCOME: What should state EXTENSION SERVICES offer as best practices for HABITAT MANAGEMENT of pawpaw orchards and their surrounds to ensure adequate populations of POLLINATORS?
• RECOMMENDATIONS FOR FURTHER OBSERVATIONS AND EXPERIMENTS:1. How do the effective pollinators (such as nitidulid beetles) deposit pollen onto the female-ready tip of the receptacle? Do effective pollinators deliver pollen via particles that cling to their ventral area and/or their mouthparts? And are any of the larger insects (flies) that have pollen visible on their backs also able to deliver pollen to the receptive flower tip? And is the pollen visible on the backs of flies pawpaw pollen, or is it from another flower species?
2. How long does an effective pollinator remain on the receptacle tip? (Overall, what are the chances of actually observing a pollination event?) And where does an effective pollinator go next? Does it receive no benefit and so it simply flies off? Or does it crawl down the receptacle stalk to the nectaries and is there a food reward in the flower depth during the female receptive stage?
3. We already know that nitidulid beetles are numerous at depth during the male flower stage (and no other insect type was found at depth in Spring 2021 flower observations). But by the time Barlow and Ford began shaking the flowers over a bowl to release the hidden insects, no female stage flowers were available to test. Therefore a remaining unknown is at what flower stage do the nitidulid beetles begin crawling into the hidden nectary part of the flower, and how long do they remain there? Are there any beetles who effectively pollinate a flower, then crawl down and remain in the flower long enough to exit at a time such that they pick up a fresh load of pollen on their bellies and mouthparts?
4. Are the nitulidid beetles breeding in the flower depth? Or have some or all completed mating before burrowing into the soil to overwinter as adult beetles?
5. After leaving a male flower, is the same effective pollinator seeking another pawpaw flower and what stage of flower?
6. What is a beetle's next destination when it leaves the pawpaw orchard? Is it then seeking another food source, an egg-laying site, or both?
7. Some Annonaceae flowers offer thermogenesis as an insect lure at their depths. Downward-pointing pawpaw flowers are obviously excellent habitat for avoiding wind and rain (and possibly predators?). But is additional warming offered by the metabolic processes in the flower itself? And does thermogenesis also assist in preventing a degree of frost-kill at ambient temperatures somewhat below freezing?
8. Could native pawpaw be planted in "wild" forest settings to reduce the invasive damage being caused by the exotic subcanopy Amur honeysuckle (Lonicera maackii)? Is there evidence that established wild pawpaw patches resist invasion by the exotic? And where Amur honeysuckle has already established a subcanopy monoculture, could the planting of pawpaw seeds (with or without cutting of Lonicera stems) be a way to reduce the dominance of the invasive woody plant? Note: A basic reference is the 2016 "A review on the invasion ecology of Amur honeysuckle (Lonicera maackii, Caprifoliaceae) a case study of ecological impacts at multiple scales".
Guidance for the Future Pollinator Watches
• MODERN SCIENCE, NATURAL HISTORY, and TEK: We hope to have volunteers utilizing a spectrum of observational stances and techniques, ranging from the quantitative rigor of modern science (including citizen science), to the more qualitative emphases of the western tradition of natural history, and (if possible) Traditional Ecological Knowledge, TEK, as practiced by experienced or new learners of this Indigenous form of science and right relationship.
For those unfamiliar with the "Traditional Ecological Knowledge" (TEK), here is online access to and a lengthy excerpt from a 2002 article by ROBIN WALL KIMMERER, "Weaving Traditional Ecological Knowledge into Biological Education: A Call to Action", in BioScience:"Traditional ecological knowledge is not unique to Native American culture but exists all over the world, independent of ethnicity. It is born of long intimacy and attentiveness to a homeland and can arise wherever people are materially and spiritually integrated with their landscape. TEK is rational and reliable knowledge that has been developed through generations of intimate contact by native peoples with their lands. TEK is being recognized as having equal status with scientific knowledge (UNEP 1998) and has been termed the 'intellectual twin to science' (DeLoria 1995). This long intellectual tradition exists in parallel to Western science, yet has been historically marginalized by the scientific community.• GUIDANCE from Western Science and Natural History Perspectives
Traditional knowledge has much in common with scientific ecological knowledge (SEK), which is not surprising since both traditions derive from the same source: systematic observations of nature. Both knowledge systems yield detailed empirical information of natural phenomena and relationships among ecosystem components. Both SEK and TEK have predictive power, and in both intellectual traditions, observations are interpreted within a particular cultural context.
Traditional knowledge encompasses a wide range of biological information, which overlaps significantly with the content of a mainstream course in ecology or conservation biology. The scope of traditional ecological knowledge includes detailed empirical knowledge of population biology, resource assessment and monitoring, successional dynamics, patterns of fluctuation in climate and resources, species interactions, ethnotaxonomy, sustainable harvesting, and adaptive management and manipulation of disturbance regimes (Berkes 1999). Case histories of the utility of TEK in conservation biology span a range of biomes from the tundra to the tropical rainforest."
Traditional ecological knowledge differs from scientific ecological knowledge in a number of important ways. TEK observations tend to be qualitative, and they create a diachronic database, that is, a record of observations from a single locale over a long time period. The National Science Foundation, in its support of the Long-Term Ecological Research program, has validated the importance of such continuous data. In TEK, the observers tend to be the resource users themselves, for example, hunters, fishers, and gatherers whose harvesting success is inextricably linked to the quality and reliability of their ecological observations. In contrast, scientific observations made by a small group of professionals tend to be quantitative and often represent synchronic data or simultaneous observations from a wide range of sites, which frequently lack the long-term perspective of TEK. Additional differences between scientific knowledge and traditional knowledge are described in Berkes (1993).
Western science is conducted in an academic culture in which nature is viewed strictly objectively. In this aspect, TEK diverges significantly from Western science (Pierotti and Wildcat 2000). TEK is much more than the empirical information concerning ecological relationships. Unlike SEK, traditional knowledge is woven into and is inseparable from the social and spiritual context of the culture. Traditional knowledge can rival Western science as a body of empirical information, but traditional knowledge may also extend its explanatory power beyond the strictly empirical, where science cannot go. TEK is laden with associated values, while the scientific community prides itself on data that are "value free." TEK includes an ethic of reciprocal respect and obligations between humans and the nonhuman world. In indigenous science, nature is subject, not object. Such holistic ways of understanding the environment offer alternatives to the dominant consumptive values of Western societies (Berkes 1999, Hunn 1999). Embraced as an equal partner to the power of Western science, TEK offers not only important biological insights but a cultural framework for environmental problem solving that incorporates human values.
List prepared by science writer, Connie Barlow:
PREPARATION: TEAM AND EQUIPMENT: Based on Connie Barlow's experience Spring 2021, a pawpaw pollinator watch requires no fewer than 2 individuals at each "station". That is because, after one gently upturns a flower and records flower stage, scent, and whether insects are visible, the only way to be sure whether there are any hidden insects in the flower is to allow the flower to go back into its downward orientation, place a bowl under it, then tap the stem (or shake vigorously if necessary).
LEFT: Here is the cereal bowl that Connie Barlow and Dallas Ford used at the Maple St. site in Ypsilanti. Usually, the beetles do not immediately fly away, so we could put the bowl on the ground, count the beetles, and use cameras to record results close-up. Note one small beetle on the lower right curve of the bowl.
Read the "Pawpaw as an Ancient Flower Type" section to learn WHY EFFECTIVE POLLINATORS SPEND A LONG TIME INSIDE THE FLOWERS and thus can only be observed by shaking them out of a flower. If you just look and probe a bit, you will likely not see any of these tiny beetles.
1. FIND AN OBSERVATIONAL SITE: As you enter the orchard of pawpaw at Marc Boone's farm or the wild patch along the Saline River, prepare yourself (in whatever way is natural for you), to be patient and grateful for this opportunity to experience, learn, and possibly contribute toward new understandings. Make sure you spend quality time at the beginning exploring the site as a whole in a receptive, observant way and with the intent on finding one or more specific locales for engaging in long flower-watching sessions. Ideal sites will likely include those with many flowers on branches low enough to touch and therefore to see details up close. Therefore, pay special attention to asimen trees that have low branches with multiple flowers in different stages of receptivity. Ideally, you might come upon a branch that has both a female receptive and a male receptive flower for viewing at the same time. You may find it helpful to have a magnifying lens handy both for insect observation and for discerning the reproductive stage of flowers at your particular locale.
TEST FOR MALE RECEPTIVITY: Gently touch the anthers in a male-stage flower, and ensure that some pollen visibly sticks to your finger. Because pollen grains are released as stuck-together tetrads (4 grains together), they should be more visible than pollen from other plants.2. DOCUMENT SITE CONDITIONS: Make sure through notes, audios, and/or photos that each stem and branch where you watch for (and especially if you confirm) pollinator activity can be found again by you or another volunteer. This will enable additional visits in the months ahead for documenting whether fruits are actually developing. Pay special attention and make notes as to whether a flower-rich ramet or branch seems to be benefitting from canopy openings that enable more sunlight to reach the branch.
TEST FOR FEMALE RECEPTIVITY: See if the green 3-pronged tip glistens with liquid. If unsure, gently test with your finger to feel if wet. If you can see detail, observe whether any pollen grains are already on it and if those grains look the same as the grains on the ripe male anthers of another flower.
3. DOCUMENT FLOWER NUMBERS AND STAGE OF RECEPTIVITY at your observational site (through notes, audio, and/or photos).
4. GUIDANCE FOR OBSERVING INSECT TYPES AND THEIR BEHAVIOR: Even though the male (pollen) stage of an asimen flower follows the female stage, an effective pollinator must first visit a male-stage flower in order to pick up pollen before visiting a female-stage flower. Because the male-stage flower has both the outer and inner corolla of petals fully open, small insects (like thrips and flies) that are attracted to the smell and food value at the inner depths of the petals are likely to pick up pollen only incidentally, especially on their backs. Flies are likely to avoid the central reproductive structure ("receptacle") altogether and just land on the inside of an inner petal and then crawl upward toward the food, acquiring pollen on their backs (or none at all) while doing so. Because most insect visitors will likely be flies and because flies are not expected to be effective pollinators, it is crucial to remember what effective "flower beetles" look like and to focus your attention on those types. Crucially, WATCH FOR INSECT BEHAVIOR during your observations, with these questions in mind:• FOR MALE RECEPTIVE-STAGE FLOWERS: Do potential pollinators land on the central reproductive stalk of the downward hanging flower, and then crawl upward over the pollen-rich anthers in order to reach their goal deep inside the flower? If so, do you see them acquiring pollen on their undersides, and do they spend a lot of time deep inside the flower (even out of sight)? In contrast, do the flies (being lighter) preference landing directly on the inner petals, thereby crawling deep into the flower? And do you notice whether those flies arrive and/or leave with yellow pollen grains on their backs?5. IF YOU HAVE A SMART PHONE you may wish to instantly photo-document insect visitors for expert identification, by using the i-Naturalist online platform. Note: If photo-documentation is limited, then focus your photography on insect types that exhibit behavior likely to serve effectively for pollen gathering and transmittal.
• FOR FEMALE RECEPTIVE-STAGE FLOWERS: Do potential pollinators enter the flower by landing upside-down directly onto the tip of the central reproductive stalk? If they do, does it seem like they depart quickly, as if the female stage has an aroma that attracts a landing for belly pollen but the inner petals are still too tightly closed for beetles to access? And can you detect any pollen freshly stuck to the glistening wet flower tip right after the beetle departs? If you assess that pollinator landings on female-stage flowers are brief (perhaps even "accidental"), then make sure you pay a much closer watch of the female-stage flower than the male-stage (and alert other observers to do the same.)
6. DETAILED OBSERVATIONS OF INSECT BEHAVIOR: While the crucial observation on male-stage flowers is to discern whether an insect visitor acquires pollen, and where pollen sticks on its body, it will also be very interesting for observers to attempt to interpret what the insect pollinator gains during its visit. Possible gains are listed on p. 688 of "Visitor or vector?", by Thomas Sayers et al., 2019, in Arthropod-Plant Interactions. These benefits for insects include: pollen as food; nectar and/or floral tissue (inner thickened base of petals) as food; or conspecifics for potential mating. No gain (that is, deception) is also listed as a possibility, but other papers on Asimen clearly identify at least the inner petal base as a food source. However, the inner petal base is inaccessible to beetles during the phase of female receptivity, so it is possible that food reward occurs only during the male phase which would account for only very brief beetle landings on early stage flowers, as photographs reveal that flowers of different stages occur even on the same branch. Thus, a possible outcome of close observation could be food reward during the male stage, but aroma-induced deception during the earlier female stage.
Appreciating Asimen: Geography and Taxonomic Relatives
PHOTO LEFT: Annona muricata is a tropical relative of American Pawpaw.
Asimina triloba is the northern-most species of a huge tropical fruit family: Annonaceae. This family entails 108 genera and some 2,400 known species, including the fruits known as cherimoya, custard apple, soursop (photo left), and annona.
About 900 species are Neotropical, 450 are Afrotropical, and the remaining are Indomalayan. Learning more about asimen's ability to thrive at its poleward extreme (and perhaps beyond) is thus an important aspect of this project.
Annonaceae is the largest taxonomic family within one of the most ancient orders of flowering plants: Magnoliales. Genus Asimina bears a classic magnolia type flower. Opening downward keeps this long-lasting flower viable despite episodes of rain, during which it becomes an attractive rain shelter for insects. As with its presumed early ancestors, magnolia type flowers specialize in attracting beetles as pollinators.
This deep-time, planetary understanding (and wonderment!) of Asimen's place within its vast and ancient family are gifts from the sciences of paleoecology and evolutionary biology.
The concept of elder, drawn from Indigenous thinking and experience, amplifies regard for Family Annonaceae and its member species. From a now-classic TEK paper, "Traditional Ecological Knowledge" (published in 2000 in the journal Ecological Applications), Raymond Pierotti and Daniel Wildcat wrote,"In nearly all native stories animal- and plant-persons existed before human-persons. Thus, these kin exist as our elders and, much as do human elders, function as our teachers and as respected members of our community. Acknowledging nonhumans as teachers and elders requires that we pay careful attention to their lives, and recognize that these lives have meaning on their own terms."
Another tree within the Magnoliales order that bears a similar and very large flower is also at its northern-most range in southern Michigan. Liriodendron tulipifera is not yet widespread here, but does have the capacity to become the tallest tree of all.
LEFT: Native range of Liriodendron tulipifera.
Its common name, Tulip Tree, is appropriately descriptive. (See photo below.) However, another common name for this tall, fast-growing canopy species is Yellow Poplar. Perhaps this tree was called "poplar" by the settler population from England because its large leaves jostle in the wind like members of genus Populus: cottonwoods and aspens. Because this name suggests faulty affinities, it is important to call this species Tulip Tree or its lovely genus name, Liriodendron.
Photo left by Robert Miller; right by Connie Barlow
This genus has only a single species in North America, and one in Asia. A European species was wiped out during glacial times, as were many other plant species that were geographically blocked from moving southward by Europe's rugged E-W mountain ranges and the Mediterranean Sea. Hence, observing wild Tulip Tree is an opportunity to reflect with gratitude on the north-south orientation of our gentle Appalachian mountains and the major river systems that quickly delivered seeds southward as the glaciers advanced.
MAPS SOURCE: TorreyaGuardians.org
Tulip Tree has thus far not been harmed by any of the insects translocated from another continent (unlike other canopy dominant trees, such as Ash, Beech, and Elm). Moreover, although American Chestnut was the canopy giant in the 19th century in much of eastern North America, Tulip Tree took the lead when chestnut blight made its way through the forests. As well, given continuing climate disruption, there will be opportunity for Tulip Tree to be welcomed into more forests of southern Michigan and increasingly northward beyond its current range.
THE FRUIT OF ASIMEN IS PEST-FREE.
Because the leaves and twigs are not browsed by any native vertebrate, deer are no threat to seedlings and saplings. See "Intensive Selective Deer Browsing Favors Success of Asimina triloba (Paw Paw), a Native Tree Species", by Mitchell Slater and Roger Anderson, 2014, in Natural Areas Journal.
Hence asimen is an ideal native fruit for organic farming and the localizing movement in southern Michigan.
Although pawpaw is the exclusive host to the caterpillar stage of our Zebra Swallowtail butterfly, finding this native in a pawpaw patch is a rare delight.
Eurytides marcellus is the only member in the temperate zone of the otherwise large tropical group of swallowtail butterflies known as the "kite swallowtails" (tribe Leptocircini).
PHOTO LEFT: Zebra Swallowtail laying an egg on a pawpaw stem.
Appreciating Asimen: Fully resists deer browsing
Land use in southern Michigan offers ideal habitat for uncontrollable population growth by deer: Our patchwork of small woodlots and forested river edges amidst farm fields, large rural properties with lawns and gardens, and abundant roads provide edge habitats favored by deer. Dwellings and people are interspersed such that opportunities even for bow-hunting (much less rifles) are difficult to arrange. As well, once the sound of rifles begins, deer can be expected to retreat to hunting-free safe zones that they have experienced in the past.
Overall, so long as traditional carnivores are missing and hunting is not a year-round activity, winter starvation, disease, and collisions with cars are what controls the deer population. Meanwhile, the native palatable plants are all but lost and the deer-resistant non-natives take over.
Most worrisome for foresters is that canopy trees will not be able to replace themselves wherever deer are overpopulated: their seedlings and saplings are killed by perpetual browsing.
LEFT: Invasive Amur honeysuckle, Lonicera maackii from Asia is now a dominant subcanopy woody tree/shrub in many recovering forested zones in southern Michigan.
This photo, taken in early spring, along the Huron River near Ypsilanti, shows a dense patch of the mature honeysuckle.
The shade is now too dense for the fallen canopy tree in the background to be replaced by native canopy trees.
According to scholarly papers, there are only three native subcanopy trees in Michigan that can, to a large extent, grow and maintain despite overpopulated deer: PAWPAW, striped maple, and American hornbeam.
• News article, 2023, "Few good options for shrinking Michigan's problem deer herds". EXCERPT: "... Beyond risk of crashes and disease, deer can destroy forest ecosystems, suburban hosta gardens and farmers' crops. One study found that in Presque Isle County alone, deer consumed a tenth of farmers' soybeans. In overbrowsed forests, saplings disappear and mature trees have a manicured look from deer nibbling branches as high as their necks can reach. That eliminates habitat for ground-nesting songbirds and other animals..."
• "Impacts of White-Tailed Deer Overabundance in Forest Ecosystems: An Overview", 2008, by Thomas J. Rawinski, USFS. EXCERPTS: "Deer have successfully exploited the human-altered environment, feeding in agricultural fields, orchards, roadsides, lawns, and gardens... The forest floor is presently dominated by unpalatable plant species, such as black huckleberry, Japanese barberry, Pennsylvania sedge, and various woodland grasses. As trees mature and die, or topple over during storms, gaps in the canopy become larger and more numerous. There are no young trees to fill the gaps.... Some plants resist deer herbivory, owing to chemical or morphological defenses or low digestible content. Among tree species, black cherry would be classified as fairly resistant. Horsley and others (2003) demonstrated a trend toward black cherry dominance in forests impacted by deer. At Rock Creek Park in Washington, D.C., Rossell and others (2007) found all major woody species to be impacted by deer, with the exception of American beech and spicebush. At very high population densities deer will ultimately browse black cherry, American beech, spicebush, mountain laurel, and many other less palatable species....Native herb populations are often decimated by deer, but some species are consistently avoided. Examples [of native species avoided by deer] include white snakeroot, black bugbane, mayapple, blue cohosh, Pennsylvania sedge, and eastern hayscented fern. A forest understory dominated by deer-resistant species is usually diagnostic of a forest afflicted by overly abundant deer. Foresters are especially concerned that eastern hayscented fern has become too abundant in some areas, preventing or impeding tree seedling establishment (Horsley and others 2003)."
• "Overabundant deer and invasive plants drive widespread regeneration debt in eastern United States national parks", 2023, by Kathryn M. Miller et al., Ecological Applications. EXCERPT: "... Many of these browse-tolerant species, like paw paw (Asimina triloba), American holly (Ilex opaca), and American hornbeam (Carpinus caroliniana), are short-stature trees that are unable to grow to current canopy height..."
• "Compounding human stressors cause major regeneration debt in over half of eastern US forests", 2019, by Kathryn M. Miller and Brian J. McGill, Journal of Applied Ecology EXCERPT: "... For example, several low canopy, browse-resistant species (e.g. striped maple and pawpaw) have shown increases in areas with high deer densities, which can further suppress regeneration of canopy species and greatly alter forest structure (Kain et al., 2011; Rossell et al., 2005)."
• Anecdotal report by Laurie Potteiger, West Virginia Native Plant Society: "Does anyone have experience removing/controlling pawpaw trees? We won't get to planting trees or shrubs until this fall or next year and in the meantime they have/are taking over. What should I do in the meantime? More background: I live in an area (Jefferson County, near Harpers Ferry at about 700' elevation) with an extremely high deer population. The deer eat virtually every other native tree and shrub. Even spicebush. There are virtually no saplings of trees other than pawpaw, although the overstory contains tulip poplars, maples, oaks, hickories, etc. The seedlings for those other native species don't get more than an inch or two high before the deer eat them. We have an acre of mostly wooded land (on the top of the ridge and downslope facing NW). Pawpaw are already dominant in some areas, and popping up where they are not yet dominant, but grow way faster than anything else. We have been planting some native forbs, and have planted a few shrubs and trees, but have to cage or fence everything I plant to protect them for the deer. (When I find a tiny tree seedling other than pawpaw I try to cage it before the deer get to it.) The goal is to eventually put an 8' deer fence around a significant portion of the property rather than having all the individual-plant cages and the multiple deer exclosures, which still leave most of the area unprotected. Also: most of my outdoor time in spring the last two or three years has been pulling garlic mustard (along with several other invasive non-native plants). But making significant progress. I've already started cutting down some of the young [pawpaw] trees (leaving a stump so I know where they were) but I've read that only stimulates more growth. And I've read painting stumps with glyphosate in fall doesn't really help kill the tree the way it does with many other trees and shrubs. What to do?"
Appreciating Asimen: Prevents Invasion by Japanese Stiltgrass
In 2017, Michigan DNR reported first detection of invasive Japanese Stiltgrass in this state. Resembling a small bamboo, Microstegium vimineum was spotted in Washtenaw County. Wikipedia reports that it arrived first in Tennessee, as packing material for porcelain from China, in 1919.
Japanese stiltgrass is similar to and often grows along with the North American grass Leersia virginica.
A silver stripe running down the center of its leaf (PHOTO LEFT) is diagnostic of this non-native grass.
Also, Leersia flowers one to two months earlier than the stiltgrass, which flowers in late summer.
Connie Barlow reports seeing dense patches of a similar-looking grass while walking the pawpaw patch at Draper-Houston. But she quickly learned by observation that if such a grassy patch is present, there will be no pawpaw stems there.
Fortunately, a 2004 report confirmed that in Tennessee, "Dense M. vimineum cover stopped abruptly at the drip line of the A. triloba patch and was absent beneath the A. triloba canopy.... Whereas overstory tree canopy apparently facilitates the establishment of this shade-tolerant grass, the interaction of overstory canopy with midstory canopy interferes with M. vimineum by reducing the availability of sunflecks at the ground layer." Ref: "Light limitation creates patchy distribution of an invasive grass in eastern deciduous forests", by Patrice Cole and Jake Weltzin, 2005, in Biological Invasions.
Appreciating Asimen: Ethnobotany
Photos by Connie Barlow
ABOVE: Connie Barlow purchased this box of native pawpaw and persimmon at the U-pick orchard of Marc Boone, near Ann Arbor MI, early October 2020.ASIMEN is not only the largest fruit in America, it also excels in taste and nutrition, as in this characterization by Sheri Beth Crabtree, in her master's thesis at the University of Kentucky, 2004, titled "Sexual and Asexual Reproductive Characteristics of the North American Pawpaw":The fruit is very sweet, with a strong aroma when ripe and soft custard-like flesh. The flavor of the pawpaw fruit is unique, having been described as resembling banana, mango, pineapple, or melon. The fruit are also highly nutritious, containing double the vitamin C of apples, peaches, or grapes, amounts of vitamin A similar to apples and grapes, higher levels of many minerals, including potassium, phosphorus, magnesium, calcium, and iron, than apples, peaches, or grapes; and high levels of several essential amino acids (Peterson et al., 1982).There are many references to INDIGENOUS and EARLY SETTLER uses and appreciation of pawpaw fruit. For example:"Some Native American tribes cultivated the pawpaw for fruit and are responsible for its widespread range today. The Cherokee and many other tribes used the pawpaw fruit for food. The fruit, which is the largest edible fruit native to America, is high in amino acids. The Iroquois used the mashed fruit to make small cakes that were dried and stored. The dried cakes were soaked in water and cooked to make a sauce or relish that was served with corn bread. Raw and cooked fruits were dried by the sun or on a fire. These were stored for use in the future or taken on hunts. The Cherokee used the inner bark to make cordage. By twisting the bark, they made string and strong ropes." Excerpted from "USDA Plant Guide: Pawpaw".
"The pawpaw has a rich history as an important food source to Native Americans, early European explorers, and early settlers of North America (Pickering, 1879). Native Americans likely aided in the distribution of pawpaw across North America, with evidence of the Iroquois tribe bringing pawpaws into central New York, where they were not found previously (Keener and Kuhns, 1997). The pawpaw was first formally noted in 1541, by the De Soto exploration group in the Mississippi River valley (Sargent, 1890). Lewis and Clark wrote in their journal that when rations were low, their exploring party subsisted mostly on pawpaws, and enjoyed the taste (Pomper and Layne, 2005). Early settlers depended partially on pawpaw to sustain them in times of crop failure (Peterson, 1991)." Excerpted from "Sexual and Asexual Reproductive Characteristics of the North American Pawpaw [Asimina triloba]", master's thesis by Sheri Beth Crabtree, 2004, University of Kentucky.
"There is evidence that humans played a role in pawpaw dispersal as well. 'Natives in the eastern half of the country have always used pawpaws,' said Dr Devon Mihesuah, a citizen of the Choctaw Nation who holds the Cora Lee Beers Price professorship in International Cultural Understanding at the University of Kansas. 'Iroquois reportedly mashed pawpaws and made the flesh into cakes and then dried them in the sun. They were used as a travel food or mixed with water into cornbread.'" Excerpted from "The revival of a forgotten American fruit", by Jonathan Shipley, 2022, BBC Travel.
Connie Barlow queried a friend, Lamar Marshall, who documented the traditional trail system of the Cherokee, using archived texts and maps followed by field investigations of each. His work was sponsored and is owned by the Eastern Band tribe of Cherokee in western North Carolina.LAMAR MARSHALL replied to Connie 2 April 2021: "... Regarding pawpaws, we don't have near as many in the Southeast as the central and northeast states. They occurred down through Alabama but they rarely fruit there and here in the Blue Ridge. I was told by old timers down in Alabama that pawpaw was used for firemaking and cordage. We used it extensively for hand drills and fire boards. One of the best and softest for getting coals fast. As far as primary sources, very few in my possession and I haven't checked the archaeological research from those recovering seeds and food remains in fire pits. U.T and Chapel Hill folks have done a lot. I attached two references you likely have. One from the encyclopedic Native American Botany by Moerman and the other Plants of the Cherokee by William Banks. The latter is from a thesis done about 1950 with the author actually gathering first-hand data from Cherokees. It includes the Cherokee name. I have attached excerpts from both books. If I find anything further, I will get it to you."
John Ambrose, a retired botanist in southern Ontario Province, wrote in an email (4 August 2021) to Barlow:"I remember thinking that the pawpaws in s. Ontario must have arrived by canoe; all are delicious and the ones in the US are sometimes said to be insipid, so some human selection likely has taken place, plus almost all Ontario populations occur in river floodplains."An excellent academic paper that aggregates previous studies in listing pawpaw among some 20 native fruit and nut trees planted by the Indigenous prior to European colonization is: "Native Americans as active and passive promoters of mast and fruit trees in the eastern USA", by Marc D. Abrams and Gregory J. Nowacki, 2008, The Holocene:Fleshy tree fruits were used for complex carbohydrates, vitamins and minerals and at least 20 fruit- and berry-producing trees native to the eastern USA were commonly consumed by Native Americans (Table 1). In the southeast USA, persimmon (Diospyros virginiana), elderberry (Sambucus), hackberry and sugarberry (Celtis), hawthorne (Crataegus) and pawpaw (Asimina triloba) were most accessible (Fogelson, 2004: 62). They eliminated the astringent taste of persimmon by leaving the fruit on the tree until after the first frost (Briand, 2005). Fruits and berries could be eaten in season or dried and used throughout the year (Lieberman, 1984). Cherokees girdled trees and used fire to clear areas to stimulate production of woody shrub and vines important to their diet, such as raspberry, elderberry, blackberry, blueberry, huckleberry and grapes. They ate wild cherries (Prunus), pawpaw, mulberry (Morus), serviceberry (Amelanchier) and persimmon. Creek Indians ate fruits of plum (Prunus), mulberry, persimmon and honey locust pods (Fogelson, 2004: 375-76). Seminole Indians in northern Florida were reported to have large groves of wild sour orange (Citrus aurantium; introduced by the Spanish) near their villages, and their diet also included native fruits of wild plum, wild cherry, pawpaw and the berries of many shrubs (Fogelson, 2004: 342, 431, 456).Tim MacWelch, published this survivalist advice 27 August 2021 in Outdoor Life magazine: 9 Reasons the Pawpaw Is the Ultimate Tree for Survivalists.
... The northern migration of pawpaw to Ohio and New York was thought to have been facilitated by Iroquois transport and planting (Keener and Kuhns, 1997), but it was later argued that the distribution of the species could be explained by mammal dispersal (Murphy, 2001).EXCERPT: "7. Make a Friction Fire: Pawpaw gave me one of the best results I have ever had in front of a class with a field-built bow drill set. While taking a class to look for friction fire equipment along a river's edge, a small pawpaw grove just kept giving and giving. I found some great branches for a drill and board that were both dead and dry, but not rotten. I was able to find another branch that was flexible enough for a bow. I stripped off some very rotten fibrous bark for tinder, and less rotten bark for cordage on the bow. The only part that wasn't pawpaw was my handhold block, which was a local piece soapstone that I drilled out with a small chunk of harder stone. The whole kit came together in roughly 30 minutes, but the most astounding part of the demo was the part where it worked on the first try. Field-built kits often need tweaking and part substitutions before they start working, but that sweet little kit worked right away (which, as any instructor will tell you, usually doesn't happen when people are watching). Pawpaw can give you great wood for friction fire components like drills and boards. As we've already discussed, the rotten bark can also be found in stages of decomposition that allow it to be both tinder and cordage material. You could even use branches as bows and chunks of wood for handhold blocks."
Pawpaw: In Search of America's Forgotten Fruit
This 296-page book by Andrew Moore was published in 2015 by Chelsea Green. It surveys past and current uses and appreciation of asimen by indigenous cultures and early settler cultures. Chapters 13-19 survey past and present human relationships with asimen region by region. "Pawpaw is ancient and belongs to an earlier culture." (p. 86)
Pages 9-10, 155: brief survey of indigenous ways of preparing and preserving the FRUIT of asimen, including drying the pulp for later use, and its nutritional values.
Pages 11, 172, 223: Indigenous uses of fibrous INNER BARK for rope, nets, and footwear were widespread in the eastern USA.
Page 83 (and other pages): Asimen is ideally suited for wild gathering in that its foliage is not browsed by deer and its fruit hosts no insect larvae.
The beginning chapters of Moore's book reveal that the pawpaw cultivars now sold by nurseries and planted in commercial orchards were selected by the dominant culture barely a century ago from wild patches. Very little, if any, subsequent breeding ensued. (Nurseries propagate cultivars not from seed but by grafting cut stems onto rootstock; this ensures stable fruit qualities.)
Because these cultivars trend from northern states (like Indiana, Illinois, Ohio, and Michigan), evidence is strong that native Americans not only greatly assisted pawpaw in migrating as far north as climate warming enabled, but also selected seeds from their preferred patches. The first peoples thus engaged in horticultural selection of pawpaw for human consumption, just as they did for traditional crops of squashes, beans, and maize.
In 2021, a photo-rich essay summarizes the horticultural history of pawpaw from the standpoint of colonial, settler culture: "The Mad Scientist of Pawpaws", by Bill Heavey, February 2021, Garden and Gun Magazine.
Toward Renewing and Expanding Reciprocity
PRACTICAL OUTCOMES: Might this field study yield results that help recover reciprocal interactions for assisting asimen in the wild, along with renewed gathering opportunities for humans?Q: If the wild patch is missing pollinators, will we find ways to encourage pollinators to return?
Q: If the wild patch lacks genetic diversity and thus cannot self-fertilize, will we offer the patch seeds from elsewhere?
Q: If the patch is too shaded to bring fertilized flowers into fruit, will we seek out where and how to offer canopy breaks?
Q: But if this ancient wild patch regards seeds as a necessity only following disturbance, how will we hear that and how will we respond?
And just who is WE? And by what process will discernment be undertaken?
If and when these questions arise from the results of our field studies, surely this is where participants immersed in western science and natural history worldviews will choose to hear from (and defer to) participants and advisors grounded in Traditional Ecological Knowledge (TEK). Botanist Robin Wall Kimmerer offers encouragement in "Restoration and Reciprocity: The Contributions of Traditional Ecological Knowledge," chapter 18 in Human Dimensions of Ecological Restoration: Integrating Science, Nature, and Culture, 2011, edited by Dave Egan et al."The idea of reciprocity with land is fundamental to many indigenous belief systems. Indeed, such beliefs serve as the foundation for what have been described as cultures of gratitude. In such cultures, people have a responsibility not only to be grateful for the gifts provided by Mother Earth, they are also responsible for playing a positive and active role in the well-being of the land. They are called not to be passive consumers, but to sustain the land that sustains them. Responsibilities to the more-than-human world are simultaneously material and spiritual, and, in fact, the two are inseparable. Ecological restoration can be viewed as an act of reciprocity, where humans exercise their care-giving responsibility for ecosystems."• REVITALIZING HUMAN RECIPROCITY WITH THE FRUITS OF ASIMEN. There is little debate that humans in North America have been crucial dispersal agents for helping Asimen track the warming climate northward as the glaciers retreated. Whether or not seeds were intentionally selected, carried, and planted, it is indisputable that,"As the ice retreated from its last southward advance, which peaked about twenty thousand years ago, four of the five above-mentioned anachronistic trees of eastern and central North America would have been helped to reclaim former territory by newly arriving humans. Pawpaw and persimmon fruits would have been carried back to camp, their seeds removed or spit out at the time of eating." Connie Barlow, 2001, "Anachronistic Fruits and the Ghosts Who Haunt Them", Arnoldia• WIKIPEDIA "Asimina triloba": "The natural distribution of the common pawpaw in North America, prior to the ice ages and lasting until roughly 10,000 years ago, was done by certain megafauna until they became extinct during the Quaternary extinction event. After the arrival of humans and the subsequent extinction of megafauna that were distributing A. triloba, the probable distribution of these large fruit-bearing plants has been by humans."
• "Ecological niche modelling and phylogeography reveal range shifts of pawpaw, a North American understorey tree", by Graham E Wyatt et al., 12 January 2021, in Journal of Biogeography.ABSTRACT: Predictions of species' responses to accelerating global climate change require an understanding of historical range shifts. However, large-scale phylogeographical studies of Eastern North American understorey plant taxa are relatively scarce. Here we employ ecological niche modelling and genetic analyses for inference of optimal pawpaw habitat in the past and future.... Models suggest that 22,000 YBP A. triloba was restricted to two major refugia in narrow bands of mostly now-submerged habitat and possibly several small inland refugia. Molecular data are consistent suggesting that the eastern refugia expanded to give rise to the eastern cluster which is characterized by higher genetic diversity. The Gulf of Mexico refugium likely gave rise to populations in the western cluster, which is characterized by lower genetic diversity.
22,000 years ago Year 2070 projected range
ABOVE: Green signifies the geographic range of the most suitable habitats past and future. LEFT: Refuges for pawpaw during last glacial maximum, 22,000 YBP (low sea level at that time enabled retreat to coastal areas now underwater). RIGHT: Projected ideal range in 2070 (using IPCC high emissions scenario)."Given the low fruit-set observed in populations at the northern edge of the current range (Wyatt, unpublished data) and limited vagility of contemporary seed dispersal vectors (gravity and small mammals), A. triloba is unlikely to expand its range rapidly and track environmental changes in lockstep.... Although our models indicate that optimal habitat will expand significantly, between the possible loss of southern populations and environmental change that outpaces the rate of dispersal and colonization at the northern edge, the realized distribution of A. triloba may diminish by 2070."
"Helping Forests Walk"
Assisted Migration Experiments for Pawpaw
As with many native trees, horticulturalists have inadvertently established ongoing experiments in learning just how far north pawpaw may be able to survive (even thrive well enough to perhaps produce fruit with viable seeds) in today's climate. Establishing pawpaw in suitable ecological habitats northward is a great way to ensure that this ancient and wondrous subcanopy tree will indeed pass through the bottleneck of unnaturally rapid, human-caused climate change.
Locales of such horticultural plantings will be added to this page, whenever the editor is alerted to their existence (especially along with photos) such as the two below.
ABOVE: Oct 2022 - Pawpaw planted near Hayward, Wisconsin (Oct 2022).
LEFT: Pawpaw planted in southern Quebec, Canada (Oct 2022).
BELOW: Connie Barlow winter-stratified seeds from fruit harvested Fall 2022 in a pit dug into a well-drained forested slope near her home in southern Michigan. The last week in May 2023 the seeds were dug up, boxed, and mailed 5 days later. After 2 weeks, the boxes arrived at the homes of two planters in Canada: Ottawa (left) and Nova Scotia (right). Some seeds had germinated enroute.
ABOVE: It took 2 weeks for seeds sent priority mail from southern Michigan to reach 2 destinations in eastern Canada. During that time, 28 of 59 seeds germinated enroute to Ottawa, Ontario (left), and 14 of 60 germinated enroute to Nova Scotia (right).
Could pawpaw help compensate
for the loss of Black Ash as a fiber source?
BLACK ASH PAWPAW Note: The WIKIPEDIA page for Black Ash states: "Black ash is unique among all trees in North America in that it does not have fibers connecting the growth rings to each other. This is a useful property for basket makers. By pounding on the wood with a mallet, the weaker spring wood layer is crushed, allowing the tougher and darker summer wood layer to be peeled off in long strips."
Could the fiber qualities of asimen inner bark help compensate for the immense cultural loss of fiber wrought by the Emerald Ash Borer's impact on Black Ash trees (Fraxinus nigra)?
If so, would reciprocity entail helping asimen to move northward into culturally significant woodlands in which Black Ash has been lost?
One woman in northern MICHIGAN seems to have initiated that experiment. The Little Traverse Bay Bands of Odawa Indians are already planting tree species onto their lands whose northern-most range is several hundred miles southward. One of those trees is pawpaw:
• "As northern Michigan warms, scientists bring tree seedlings from the south", by Kelly House, 3 May 2021, in Bridge Michigan.
"RENEE DILLARD is a member of the Little Traverse Bay Bands and a renowned Anishinaabe natural fiber artist known for her intricate black ash baskets. She had to stop harvesting ash in northern Michigan's swamps after the emerald ash borer decimated the population. She switched to other fiber, including cedar, dogbane, basswood and bullrush. But climate change threatens to push some of those species northward, too, and Dillard believes they'll eventually become scarce near the Little Traverse Bay Bands' land in the Northwestern Lower Peninsula.
So she is experimenting with substitutes from further south. She keeps a stash of pawpaw seeds, and occasionally buries a few near her home in Harbor Springs, hoping they'll grow into the deciduous tree nicknamed 'the Indiana banana' for its custardy, tropical-tasting fruit. But it's the fibrous bark Dillard is after...."
"...NOAH JANSEN's tree migration project is aimed at facilitating this kind of cultural resilience. He has specifically chosen plants that could preserve tribal members ability to hunt, gather and carry on cultural traditions: There's sassafras, a species with medicinal properties. And American plum, which can be harvested by humans or grazed by deer.
As foliage on the forest canopy matures, tribal species managers hope to continue their efforts by filling in the understory with plants that can survive in the future climate. Similar experiments are taking place or planned in communities throughout the state."
Could pawpaw help restore the subcanopy
where deer are overpopulated?
ABOVE: Connie Barlow took these photos November 2021 while planting pawpaw seeds onto the forested slopes along the Huron River where it flows through collapsed industrial landscapes of Ypsilanti, Michigan. All green leaves in these photos are of a non-native honeysuckle: Lonicera maackii. This exotic Amur honeysuckle is the dominant subcanopy woody plant in these photos. Notice the distinct longitudinal-ridged bark of the foreground stem in the left photo and the opposite leaves with red berries in the right. Uniquely, here in Michigan this invasive deciduous plant retains bright green leaves that simply fall off in December without browning or yellowing.
HYPOTHESIS: Might the foreign honeysuckle express so invasively because overpopulated deer eat virtually all of the seedlings of our native trees that attempt to grow? Yet, because pawpaw is poisonous to deer, might our native subcanopy tree be able to effectively compete with (possibly even wrest control from) the now-dominant subcanopy invasive?
SCIENTIFIC REPORTS OF PAWPAW THRIVING WHERE DEER ARE OVERPOPULATED:• "In recent decades, naturalists have noted the expansion of pawpaw from well-drained, lowland habitats into drier, upland forests. This phenomenon appears to be driven, at least in part, by patterns of deer browse. Deer find pawpaw foliage unpalatable and, therefore, avoid browsing pawpaw seedlings and saplings. Instead, they preferentially browse species such as spicebush (Lindera benzoin), oaks (Quercus spp.), red maple (Acer rubrum), and blackgum (Nyssa sylvatica).... This deer behavior benefits pawpaw in two ways. First, small pawpaws don’t need to allocate energy to recovering from browse, and instead can put that energy towards growth and reproduction. Second, frequent deer browse on sapling and shrub species preferred by deer suppresses the growth of these species, clearing the way for pawpaw. As a result, we might expect to see pawpaw becoming more common in forest understories that are heavily impacted by deer browse (which describes most NCR forests).... Another potential contributor to the success of pawpaw is the suppression of fires that were an important part of the disturbance regime in many eastern forests before European settlement. Pawpaw are not strongly fire-adapted (unlike other common canopy dominates, such as oaks), and they likely benefit from the lack of fire in contemporary forests." National Park Service webpage: "Pawpaw: Small Tree, Big Impact".
• "Indiana state parks historically did not allow hunting. But by the 1990s, white-tailed deer populations in parks had swelled to such size that many species of native wildflowers such as trillium and lilies largely disappeared, replaced by wild ginger and exotic species such as garlic mustard and Japanese stiltgrass, plants not favored by deer. Oak and ash tree seedlings gave way to highly deer-resistant or unpalatable trees such as pawpaw." 2014, "Hunting gives deer-damaged forests in state parks a shot at recovery".
• "Although white-tailed deer are generalist herbivores, they can have significant effects on species composition and abundance of forest trees, especially when deer densities are high and most plant species are heavily browsed but a few are selectively avoided as browse. We evaluated effects of selective deer browsing on tree species abundance in an old-growth mesic/wet-mesic forest in central Illinois.... The study site has high deer density (75 deer km2) during winter months, and initial observations indicated that pawpaw (Asimina triloba (L.) Dunal) was strongly avoided as browse. Paw paw density increased in the seedling stratum between the two sample periods. However, nearly all other tree species declined in density" 2014, "Intensive Selective Deer Browsing Favors Success of Asimina triloba (Paw Paw) a Native Tree Species".
ABOVE: In contrast to the invasive Amur honeysuckle, a pawpaw subcanopy welcomes native spring ephemeral herbs. (Photos by Connie Barlow, 2 May 2021, Draper-Houston Meadows Preserve.)
WHERE TO PLANT PAWPAW SEEDS FOR FOREST HEALTH AND REWILDING: Pawpaw likely has a much greater habitat capability than just the strips of sloping and raised areas near a river. Rivers likely became the dominant means for pawpaw seed dispersal when the megafauna disappeared and even moreso when black bears retreated as Euro-American colonizers arrived and began farming and grazing operations.
Below is a natural history observation about a wild, fruit-producing pawpaw patch in an upland forest in southwestern Virginia. The email came from Sharon Mohney, sent on 17 December 2021:"... This year was my best pawpaw season so far, and I missed probably half of them due to having to go out of town. You'd think a lot of wildlife would eat them, but they tend to just rot on the ground if I don't get them, although wasps and bees get some of them, and I found a box turtle eating one once. It's surprising to me that the deer, bear, possums, and raccoons around here don't scoop up all the pawpaws before I get a chance at them, but they don't.• VIDEO: "Helping Subcanopy Trees Migrate" - 50 minutes - published November 2021
In recent years I've noticed a lot of pawpaws showing up on higher drier sites on our place. I didn't think much about it until I noticed that my "Flora of Virginia" phone app also makes note of this development: "In recent decades, this species has expanded into dry-mesic or even dry upland habitats and increased in abundance in many areas. The reasons for these changes are not clear but could include fire exclusion and the plant's unpalatability to white-tailed deer (and the deer's selective browsing on competition.)"
I've had good luck planting pawpaw seeds soon after I clean the fruit. I understand they don't do well if allowed to dry..."
"Helping Subcanopy Trees Migrate" features two subcanopy species of the eastern USA. Pawpaw, while having a long north-south reach in its historic range, can benefit from "assisted range expansion" northward. Florida Torreya is an endangered glacial relict for which citizens, including Connie, have done what the official recovery program implementers have been unwilling to do restore its health by nothing more difficult than planting seeds well to the north.
Indigenous values are advocated as well as the "natural history" style of observation and interpretation.
Where Pawpaw is a "Threatened Species"
State of New York
Washtenaw County MICHIGAN is the source and focal location where the idea for this Pawpaw Pollinator Watch project began. Opportunities for applying results are direct and obvious for indigenous peoples and thus there is great potential for enhancing reciprocity on tribal lands in this state. Study results may also benefit commercial growers of pawpaw in any state.
It is probably a stretch, however, for managers of natural areas "preserved/protected" by dominant culture to consider "intervening" for the purpose of encouraging fruit production in fruitless wild pawpaw patches whether that action be introducing genetic diversity, creating canopy gaps, or (least interventionist) enhancing habitat for nurturing crucial pollinators. Exceptions may include where tribal groups maintain gathering rights on "ceded" lands and where such groups advocate for management interventions of public lands toward that end.
Therefore, only in a state where pawpaw is regarded as imperiled could managers of nature preserves easily draw upon arguments from the "conservation" worldview and practice for intervening in ways that could augment the wellbeing and future viability of this species. NEW YORK is such a state. This, from the pawpaw entry of wikipedia:Previous research by the same author (Tulowiecki, 2015) offers additional background by having mapped for one county in northwestern New York archeological, historic, and forest ecological evidence of the fullness of indigenous occupation and effects on the landscape. Although the focus was on mast-bearing trees (oak, hickory, chestnut) and thus pawpaw was not evaluated, this research can be used (in combination with the 2021 mapping) for identifying places to begin pawpaw restoration and enhancement in Chautauqua County:
"Modeling the geographic distribution of pawpaw (Asimina triloba [L.] Dunal) in a portion of its northern range limits, western New York State", by Stephen J. Tulowiecki, 2021, in Plant Ecology.
EXCERPT: "... Potential pawpaw habitat occurs on or near three reservations: Cattaraugus, Tonawanda, and Tuscarora Indian Reservations. Conservation or introduction of pawpaw on tribal lands may therefore present an opportunity for reciprocal restoration, described as a 'positive feedback relationship between cultural revitalization and land restoration' (Kimmerer 2011)."NOTE: Connie notified Prof. Tulowiecki, SUNY Geneseo about this Pawpaw Pollinator Watch project. While he found it "valuable and fascinating," several factors made it impossible for him to join in Spring 2021 fieldwork: (1) pawpaw patches in New York are few; (2) they are mostly on private property, (3) far from his campus, and (4) "pawpaw typically bloom in mid-May in western New York, after the end of the school year." Also, he mentioned that this being a "threatened species" in the State of New York, there may be requirements for gaining state authorization to work with this species. Nonetheless, he wrote, "I do have a few Seneca contacts that might be interested in collaborating, on the restoration side of things." Connie will post on this page if any collaborations with the Seneca in New York State (or elsewhere) do develop.
"Native American impact on past forest composition inferred from species distribution models, Chautauqua County, New York", by Stephen J. Tulowiecki and Chris P.S. Larsen, 2015, in Ecological Monographs.
What About American Persimmon?
PHOTOS: Native range of American persimmon and its downward-facing flower.
Michigan is beyond the northern-most range of American persimmon. Even so, Marc Boone successfully grows persimmon cultivars next to his orchard of pawpaw in southeastern Michigan.
QUESTIONS: What pollinators visit the flower of persimmon, and when does the bloom occur? Overall, is there some advantage for pawpaw pollination success in having these two native fruits (both of tropical plant families) planted together? A publication of MSU Extension reports that "persimmon pollinators are unknown insects," Unusual Fruit Plants for Gardens in the North Central Region.
Finally, in a "helping forests walk" way, American persimmon (Diospyros virginiana) could be wild-planted now even in southern Michigan. Unlike pawpaw, persimmon requires full sun. Therefore, abandoned farm fields or full-sun edges of woodlots growing alongside farm or grazing fields would be the kinds of sites to look for. And even in the more southerly states, folks who value native persimmon know that the fruit is inedible before a frost ripens it. So Michigan frosts could assist the ripening process. A 1909 book, Trees Every Child Should Know, reports:"Persimmons improve, the longer they hang upon the trees. As late as January or February, little trees scarcely a dozen feet high ... are found to be hung with fruits exceptionally large and fine."This 1953 paper, "The Distribution of Diospyros virginiana", by Harry R. Skallerup (in Annals of the Missouri Botanical Garden), is helpful not only for learning the natural history of this species. Several distributional findings in this paper suggest that indigenous peoples managed lands in ways that favored persimmon. But colonizing settler takeovers of these sites meant that human assistance in preventing overtopping of sun-dependent persimmons by taller trees was lost:"... Evidently, persimmon was more of a dominant tree (as were others) in the primeval forest than it is in the second growth timber of today... Although persimmon once was known to occur in pure, dense stands, more recent reports indicate that this is now not the case. Throughout its range persimmon is reported as a minor species in older association."
Appreciating Asimen: Original Instructions
• TO DO: We seek to recruit a tribal person to guide and contribute to this section (and to ensure that the previous sections are complete and the language appropriate.) Until an indigenous author for this section arises, the below content (contributed by Connie Barlow), will need to suffice.
• "Let Our Indigenous Voices Be Heard", a 2017 document coauthored by Robin Kimmerer (Potawatomi), Ph.D., Rosalyn LaPier (Blackfeet/Métis), Ph.D., Melissa Nelson (Anishinaabe), Ph.D., and Kyle Whyte (Potawatomi), Ph.D.As original peoples, we have long memories, centuries old wisdom and deep knowledge of this land and the importance of empirical, scientific inquiry as fundamental to the well-being of people and planet.• "Mishkos Kenomagwen, the Lessons of Grass: Restoring Reciprocity with the Good Green Earth", by Robin Wall Kimmerer, chapter 3 in Traditional Ecological Knowledge, edited by Melissa K. Nelson and Dan Shilling, 2018.
Let us remember that long before Western science came to these shores, there were Indigenous scientists here. Native astronomers, agronomists, geneticists, ecologists, engineers, botanists, zoologists, watershed hydrologists, pharmacologists, physicians and more—all engaged in the creation and application of knowledge which promoted the flourishing of both human societies and the beings with whom we share the planet. We give gratitude for all their contributions to knowledge. Native science supported indigenous culture, governance and decision making for a sustainable future the same needs which bring us together today.
... Indigenous science provides a wealth of knowledge and a powerful alternative paradigm by which we understand the natural world and our relation to it. Embedded in cultural frameworks of respect, reciprocity, responsibility and reverence for the earth, Indigenous science lies within a worldview where knowledge is coupled to responsibility and human activity is aligned with ecological principles and natural law, rather than against them. We need both ways of knowing if we are to advance knowledge and sustainability.
... While Indigenous science is an ancient and dynamic body of knowledge, embedded in sophisticated cultural epistemologies, it has long been marginalized by the institutions of contemporary Western science. However, traditional knowledge is increasingly recognized as a source of concepts, models, philosophies and practices which can inform the design of new sustainability solutions. It is both ancient and urgent.
Indigenous science offers both key insights and philosophical frameworks for problem solving that includes human values, which are much needed as we face challenges such as climate change, sustainable resource management, health disparities and the need for healing the ecological damage we have done....""When we look about us on the earth, what we see is colored by our worldview and the languages that we use to describe our observations. A landscape of streams and lakes, mountains and rich valleys, shared by thousands of species of plants and animals, is understood through the lens of the western materialist worldview as a wealth of ecosystem services or natural resources. In contrast, through the lens of traditional Indigenous philosophy the living world is understood, not as a collection of exploitable resources, but as a set of relationships and responsibilities. We inhabit a landscape of gifts peopled by nonhuman relatives, the sovereign beings who sustain us, including the plants.• "Indigenous Knowledge for Earth Healing", 2018, excerpt of AUDIO interview of Robin Wall Kimmerer, May 2016, on For the Wild Podcast, with timecodes.
"... Reciprocal restoration is the mutually reinforcing restoration of land and culture, such that the repair of ecosystem services contributes to cultural revitalization, and renewal of culture promotes restoration of ecological integrity. In Indigenous communities, these reciprocal relationships may include the return of subsistence activities, the practice of traditional resource management, the restoration of traditional diets, language revitalization, and the exercise of spiritual/ethical responsibility. Concepts of reciprocal restoration also apply to mainstream society by re-engaging people with land, renewing place-based connections, and supporting cultural practices that sustain the land. Integration of TEK can support this new direction in restoration ecology, as a model for restoration of reciprocal relationships.
"... While our fluency with plant knowledge is diminishing, in both Native and non-Native communities, I have been taught that the knowledge itself is not lost. Humans may have forgotten, but the knowledge is resident in the land itself. Thus, knowledge revitalization depends as much on gaining the skills for learning from the land as it does on transmitting specific information. We need to ensure that we are educating people with the capacity to learn from the land again, to retrieve the knowledge that is held for us by the plants.... When plants are understood as teachers, it is an act of reciprocity to be an attentive student and to pass on the teachings of the plants."(27:35) "I think about Traditional Ecological Knowledge (TEK) as a way of being in a web of relationships. While nature may change, while the players may change, the stage may change, I think it's the relationship to place that endures and can guide us. So these relationships which are based in reciprocity, for example, I think will be a guide for adaptation in rapidly changing times.• The Great Lakes Indian Fish & Wildlife Commission (GLIFWC) was established in 1984, as an agency of eleven Ojibwe tribes in Michigan, Wisconsin, and Minnesota. Although these tribes may all be associated with "ceded territory" northward of Asimen's current native range, continuing climate change could make those geographic locales welcome range expansions for Asimen in the decades ahead.
"And, you know, often times we say that, as the land changes, traditional knowledge is lost. We hear this from our relatives in the north, who see their traditional knowledge threatened by climate change and by melting ice, and the disasters that are befalling them. But I've also been taught that the knowledge itself may disappear from the people, but it's not lost because that knowledge is actually resident in the land. It's the land and the rivers and the plants and the animals that are going to teach us. And it's our relationship with them that is going to enable us to learn.
"So while it's super important to maintain and revitalize traditional knowledge, I think that an element that we also have to focus on is revitalizing our ability to learn from the land to be better students of the land again."
(39:22) "Renewing our subjective relationship with place I think is at the heart of renewing that relationship of reciprocity: to see the world as made of gifts and not natural resources."
Robin Wall Kimmerer 2011, pages 257-276
"Reciprocal restoration also offers the opportunity for an immigrant culture to start becoming 'indigenous to place' by healing relationships with land and history."
"This does not mean appropriating the culture of indigenous people, but generating an authentic new relationship. It means throwing off the mindset of the immigrant, including the frontier mindset of 'take what you can get and move on.' It means becoming involved with the 'language' and dynamics of the place you live learning its landforms, weather patterns, animals, plants, waterways, and seasons."
"Being indigenous to place means to live as if we'll be here for the long haul, as if our children's future mattered. It means taking care of the land as if our lives, both spiritual and material, depended on it. It involves entering into a covenant of reciprocity with the land, which includes restoration. That's what it means to become indigenous to place."
Additional Information from Technical Papers
Prior to the Spring 2021 observation, Connie Barlow researched online the technical papers on likely beetle pollinators. Overall, effective pollinators for plants with flowers similar in structure to pawpaw are those beetles with hair-like appendages on their sides and underside. They are called "flower pollinating beetles" precisely for this reason. (See below photos.)
Photos LEFT and MIDDLE from Maryland Biodiversity Checklist • RIGHT from Matt Buckinham, Flickr 2015
ABOVE: Published scientific papers have reported two genera of scarab beetles as effective pollinators of more southerly species of genus Asimina (whose flowers are smaller than the northern species, but have similar structure): Trichiotinus (left) and, to a lesser extent, Euphoria inda (middle and right). Notice that the photo in middle shows Euphoria in the context of leaf litter. Flower pollinating beetles generally are neither carrion beetles nor dung beetles. That is, they lay their eggs not in rotting meat or dung but into rotting wood or thick leaf mulch, where larval grubs feed and eventually pupate. Key papers on Asimina species that identify beetle pollinators:• "Effects of Fire and Pollinator Visitation on the Reproductive Success of Asimina reticulata (Annonaceae), the Netted Pawpaw", by Louise K. Barton and Eric S. Menges, 2018, Castanea. (Note: Trichiotinus viridans, the "hairy flower scarab" is documented as the most prevalent visitor, and "low fruit set may be due to the lack of an effective pollinator, resulting in inbreeding depression.... Our study confirms that A. reticulata is self-compatible only if pollen is able to move among flowers, and we found that, in most cases, fruit was aborted prematurely and was found littering the ground beneath the plants.")
• "How diverse are Annonaceae with regard to pollination?", by Gerhard Gottsberger, 2012, Botanical Journal of the Linnean Society. (Note: In this paper two Florida species, Asimina obovata and Asimina pygmaea are linked with pollinating beetle species in Trichiotinus and Euphoria genera. These flowers are categorized as "diurnal without thermogenesis.")
Photos from Maryland Biodiversity Checklist, Fritz Flohr Reynolds.
ABOVE: The American carrion beetle, Necrophilia americana, requires carrion for egg-laying and its larval stage, but as an adult it will happily feed on mushrooms and fermenting pawpaw fruit. Note the lack of "hairs" on this beetle and thus its inability to serve as a pollinator.
A 2006 paper by Katherine R. Goodrich et al., "When Flowers Smell Fermented: The Chemistry and Ontogeny of Yeasty Floral scent in Pawpaw (Asimina triloba)", was published in International Journal of Plant Science. It offers evidence that carrion beetles are not involved in pawpaw pollination: "We did not detect the dimethyl oligosulfides that characterize the microbial decomposition of meat and universally constitute the odors of carrion-mimicking flowers." Instead, the authors reported a "yeastlike fragrance" in pawpaw flowers. However, "fermentation volatiles were largely absent from female-stage androgynoecia". (Many technical details in this paper may be useful for project participants.)
RECOMMENDED READING: In addition to various technical papers cited and linked here, a 296-page book on pawpaw is highly recommended: Pawpaw: In Search of America's Forgotten Fruit, by Andrew Moore, 2015, Chelsea Green.
• "The diversity and evolution of pollination systems in Annonaceae", by Richard M.K. Saunders, 2012, Botanical Journal of the Linnean Society:... There are two distinct floral forms within genus Asimina. One group (consisting of A. parviflora and A. triloba) possesses small maroon flowers that emit a foetid aroma; and the other group (consisting of all other species) possesses large, white, pink or yellow flowers that emit a more pleasant fragrance (Kral, 1960; Goodrich & Raguso, 2009). These differences clearly represent different pollination syndromes. Observations of floral visitors confirm that the foetid-smelling species are visited by small flies and/or small beetles (Willson & Schemske, 1980; Norman etal., 1992; Rogstad, 1993), whereas the fragrant species are typically visited by large beetles (Norman & Clayton, 1986; Norman et al., 1992) or rarely by flies (Uphof, 1933; Norman et al., 1992).• "Phylogenetic Analysis of the North American Beetle Genus Trichiotinus (Coleoptera: Scarabaeidae: Trichiinae)", by T. Keith Philips et. al, 2016, Psyche: A Journal of Entomology.
... Annonaceae flowers are visited by a taxonomically diverse range of insects: predominantly beetles (Coleoptera), but also thrips (Thysanoptera), flies (Diptera) and, rarely, bees (Hymenoptera) and cockroaches (Dictyoptera). Species are typically pollinated by only one of these groups, although there are several examples of species that are pollinated by more than one group, including: .... Asimina parviflora (Norman et al., 1992), A. pygmaea (Uphof, 1933; Norman & Clayton, 1986; Norman et al., 1992) and A. triloba (Willson & Schemske, 1980; Johnson & Willson, cited in Norman et al., 1992) are visited by flies and beetles.
... Despite the vast diversity of dipterans and their evident importance in pollination, there are few reports of fly pollination in Annonaceae. Flower visits by flies have only been reported for Annona (Webber, 1981b; as secondary floral visitors only), Asimina (Norman et al., 1992), Monodora (Gottsberger, 1985; Gottsberger et al., 2011), Pseuduvaria (Morawetz, 1988; Silberbauer-Gottsberger et al., 2003; Su et al., 2005) and Uvariopsis (Gottsberger et al., 2011). It should be noted, however, that Norman et al. (1992) did not observe any pollen attached to the common drosophilid flies that visited Asimina flowers (pollination resulted from visits by nitidulid beetles and rarer calliphorid flies), and that pollen transfer between flowers was not demonstrated in any of the other studies. ... To avoid confusion of stimuli, Calliphoridae (blowflies), which lay eggs in dung and carrion, favour yellow colours in the presence of sweet scents, but brown-purple colours in the presence of foetid scents (Kugler, 1956). The latter pollination system is observed in Asimina parviflora (Norman et al., 1992) and operates by DECEIT as the flies visit the flowers in order to lay eggs. Sapromyiophilous flowers, furthermore, often have partially enclosed pollination chambers that require the flies to crawl in through narrow openings (Faegri & van der Pijl, 1979).
... Adults are good fliers and forage on a variety of flowers while larvae are known to feed on various species of decaying hardwoods.... Trichiotinus is dependent upon decaying hardwoods as larval food including oak . Jackson et al.  present evidence for a split in distribution of oaks (Quercus spp.) during the most recent glacial maximum on either side of the Mississippi drainage and may be indicative of the effects of earlier glacial maxima as well. P. A. Delcourt and H. R. Delcourt [40, 41] also postulated the presence of spruce (Picea glauca) forests in the Lower Mississippi Valley. This extension south of these more cool adapted forests all the way to the gulf coast that divided the hardwood forests into eastern and western blocks was thought to be due to glacial meltwater creating a cooler climate locally .
• "Monographic Revision of the American Genus Euphoria Burmeister, 1842 (Coleoptera: Scarabaeidae: Cetoniinae)", by Jesus Orozco, 2012, BioOne Complete.
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