Pollen Specialist Bees of the Eastern United States

Jarrod Fowler & Sam Droege (2020)

Melissodes desponsus

Macropis ciliata

Colletes latitarsis

Andrena hirticincta

Introduction

This website compiles associations among native pollen specialist bees and native host plants from the Eastern United States. First, pollen specialist bees are defined and methods are described. Next, a table composed of pollen specialist bees and associated host plants is presented. Last, advice about conserving native pollen specialist bees is provided. Please note that this compilation is incomplete and in progress. Researchers are invited to add information to this website. Email records to: j@jarrodfowler.com

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Fowler, J. (2020). Pollen Specialist Bees of the Western United States
Fowler, J. (2020). Pollen Specialist Bees of the Central United States

Pollen Specialist Bees

Roughly 25% of the ~770 species of bees native to the Eastern United States are pollen specialists. Pollen specialist bees coevolved a continuum of generic to specific associations with flowering host plants or pollenizers (Cane & Sipes 2006; Danforth et al. 2019; Hurd et al. 1980; Linsley & MacSwain 1958; Robertson 1925; Wright 2018). Polylectic bees or polyleges forage pollen from unrelated plants, while oligolectic bees or oligoleges collect pollen from one family or a few related genera of plants and monolectic bees or monoleges only gather pollen from a single plant genus or species (Cane 2020; Cane & Sipes 2006; Robertson 1925).

Pollen specialist associations can mutually benefit both bees and flowers from improved foraging effectiveness and efficiency, pollen digestibility, and pollination rates, but foraging restrictions may create greater susceptibility to harm from pollination or pollenization shortages due to habitat degradation or loss, pesticides, invasive species, and climate change (Minckley et al. 1994; Packer et al. 2005; Rafferty et al. 2015). Therefore, contemporary anthropogenic threats in the Eastern United States potentially imperil native pollen specialist bee species and their indigenous host plants with population declines and extinctions through loss of species diversity.

Methods

Records of native pollen specialist bees captured or observed foraging flowers of host plants were compiled from online sources (Ascher & Pickering 2016, Hilty 2012), peer reviewed articles (Austin 1978; Bouseman & LaBerge 1978; Brooks & Griswold 1988; Cane et al. 1996; Colla et al. 2012; Deyrup & Deyrup 2011; Deyrup et al. 2002; Donovan 1977; Hall et al. 2016; LaBerge 1969, 1971, 1973, 1977, 1980, 1985, 1986, 1989; LaBerge & Bouseman 1970; LaBerge & Ribble 1972, 1975; Norden et al. 2003; Rightmyer et al. 2011; Robertson 1926, 1928, 1929; Wright 2018), technical bulletins (Krombein et al. 1979; LaBerge 1967; Mitchell 1960, 1962), and personal communications.

If bees and plants were indigenous to the Eastern United States without human intervention, then bees and plants were defined "native". Definitions of bee conservation status were averaged across ranges. If there were on average: between one and 100 records, then bees were defined "Rare"; between one and 500 records, then bees were defined "Uncommon-Rare"; around 500 records, then bees were defined "Uncommon"; between 500 and 1000 records, then bees were defined "Common-Uncommon"; around 1000 or more records, then bees were defined "Common". Conservation status may vary according to species-specific distributions and dispersions.

Bee-flower records were compared with state-level plant distributions from the USDA Plants Database (USDA NRCS 2019) and county-level distributions from The Biota of North America Program (Kartesz, BONAP 2015) and Go Botany [3.0.3] (New England Wildflower Society 2019). Our study includes only host plant genera that are native and documented as present in at least one county of at least one of the twenty regional states: Alabama, Connecticut, Delaware, Florida, Georgia, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, and West Virginia. Because plant taxonomy has undergone major recent changes, many names have been updated compared to those published in the original literature of bee-flower associations.

Results

Pollen specialist bee species of the Eastern United States are alphabetically tabulated with associated host plant families in Table 1. Six families, 10 subfamilies, 14 tribes, two subtribes, 33 genera, 55 subgenera, and 186 species of pollen specialist bees were listed. The bee family with the most pollen specialists was Andrenidae (94 spp.), while the most speciose subfamily was Andreninae (55 spp.), tribe was Eucerini (27 spp.), subtribe was Perditina (22 spp.), genus was Andrena (55 spp.), and subgenus was Eumelissodes (51 spp.). The most recurrent authorities (n = 27 authors) were Charles Robertson (1858–1935, 38 spp.), Ezra Townsend Cresson (1838–1926, 30 spp.), and Frederick Smith (1805–1879, 19 spp.). Most species were first described during years 1891 (17 spp.), 1878 (15 spp.), and 1853 (14 spp.).

The states most inhabited by pollen specialist bees were: North Carolina (144 spp.; 28% spp.), Virginia (115 spp.; 28% spp.), Georgia (112 spp.; 28% spp.), Maryland (112 spp.; 27% spp.), New Jersey (109 spp.; 27% spp.), New York (95 spp.; 21% spp.), Florida (86 spp.; 28% spp.), Connecticut (83 spp.; 24% spp.), Massachusetts (79 spp.; 21% spp.), Pennsylvania (72 spp.; 21% spp.), Mississippi (69 spp.; 29% spp.), South Carolina (67 spp.; 28% spp.), West Virginia (67 spp.; 23% spp.), Alabama (59 spp.; 31% spp.), New Hampshire (59 spp.; 23% spp.), Delaware (51 spp.; 23% spp.), Louisiana (47 spp.; 23% spp.), Maine (46 spp.; 18% spp.), Vermont (40 spp.; 18% spp.), and Rhode Island (37 spp.; 19% spp.) Of the 186 species of pollen specialists, eight spp. were recorded only in Florida, while one species was recorded in all 20 states: Melissodes (Eumelissodes) agilis Cresson, 1878. Overall, 108 bee species were considered "Rare", while 56 spp. were “Uncommon-Rare", 10 spp. were "Uncommon", 10 spp. were “Common-Uncommon", and one species was "Common". The months of activity for specialist bees relative to associated host plant flowering phenology were June (100 spp.), July (96 spp.), August (93 spp.), May (94 spp.), September (89 spp.), April (68 spp.), October (49 spp.), March (29 spp.), November (14 spp.), December (3 spp.), January (2 spp.), and February (2 spp.). Oftentimes, pollen specialist bees had only three month (55 spp.), two month (43 spp.), or four month (38 spp.) flight periods.

The most recurrent host plant family among pollen specialist bee species was Asteraceae (59 bee spp.). The most recurrent host plant genera (N = ~100) associated with pollen specialist bee species were Solidago L. (39 spp.), Helianthus L. (35 spp.), Symphyotrichum Nees (32 spp.), Rudbeckia L. (26 spp.), Chrysopsis (Nutt.) Elliott (19 spp.), Grindelia Willd. (18 spp.), Coreopsis L. (17 spp.), Heterotheca Cass. (16 spp.), Salix L. (14 spp.), Verbesina L. (14 spp.), Bidens L. (12 spp.), Pityopsis Nutt. (12 spp.), Cirsium Mill. (10 spp.), and Vaccinium L. (10 spp.).

Tables

Table 1. Pollen specialist bee families (n = 6), genera (n = 32), and species (n = 186) with taxonomic authorities, distributions according to records from 20 states (AL, CT, DE, FL, GA, LA, MA, MD, ME, MS, NC, NH, NJ, NY, PA, RI, SC, VA, VT, and WV), regional conservation status (Common, Uncommon, or Rare), phenology, and host plant families, tribes, and genera. Bee families and member genera and species are presented in ascending alphabetical order; families, subfamilies, tribes, and subtribes link to BugGuide profiles; species link to Discover Life species profiles. Month headings link to month-specific lists. Host plants link to USDA PLANTS Database genera profiles: view 'Subordinate Taxa' tabs for regional host plant species. Arthropoda: Hexapoda: Insecta: Hymenoptera: Aculeata: Anthophila (Apoidea):

* The first record for Massachusetts was from collections made and identified by M. Veit.
** Subgeneric placement and state records based in part on unpublished work by M. Arduser, J. S. Ascher, P. Bernhardt, S. Droege, R. Meier, and S.-X. Ren.
*** The first record for New England was from collections made by D. Wagner et al. and identified by J. S. Ascher.
**** The first record for Missisippi was from collections made by R. Sudan and identified by J. Neff.

Recommendations

Pollen specialist bees of the Eastern United States were most often mesolectic on Asteraceae (59 spp.) and Ericaceae (5 spp.) and monolectic on Salix L. (14 spp.), Physalis L. (5 spp.), Cornus (Swida) L. (4 spp.), Lysimachia L. (4 spp.), Oenothera L. (4 spp.), Cucurbita L. (3 spp.), Ilex L. (3 spp.), Ipomoea L. (3 spp.), Monarda L. (3 spp.), Phacelia Juss. (3 spp.), Pontederia L. (3 spp.), and Potentilla L. (3 spp.). Twenty-three unique relationships occured between individual monoleges and single host plants. Pollenizers were often either community dominant species or had ephemeral early/late season blooms, crepuscular blossoms, and odd floral morphologies.

Nearly 60% of the pollen specialist bees listed were rare. Pollinator habitat conservation and enhancement projects should prioritize practices that foster diverse communities of native pollen specialist bees and associated host plants (Fowler 2016a, 2016b). Site-specific practices including beetle banks, companion plants, cover crops, field borders, hedgerows, insectaries, meadows, pastures, prairies, and riparian buffers should be composed primarily of pollenizers for oligoleges and monoleges and secondarily of pollen and nectar plants for polyleges. Regional native plant horticulturists and nurseries should prioritize the propagation of ecoregional pollenizers for pollen specialist bees.

Conservation practices can protect native pollen specialist bees from population declines and extinctions, while identically supporting other managed and wild beneficial insects, providing wildlife habitat, reducing weeds and erosion, improving soil health and water quality, regulating pests, offering harvestable products, and bettering aesthetics (Garibaldi et al. 2014; Kleijn et al. 2015; Wratten et al. 2012). Therefore, habitat conservation and enhancement for native pollen specialist bees works synergistically to promote strong environmental, social, and economic sustainability in the Eastern United States.

Acknowledgements

Thanks to Michael S. Arduser (Missouri Department of Conservation), John S. Ascher (National University of Singapore), Daniel P. Cariveau (University of Minnesota), Mark A. Deyrup (Archbold Biological Station), Charles S. Eiseman (freelance naturalist), Jason Gibbs (Michigan State University), Clint Gibson (University of Florida), Glen Hall (University of Florida), Robert P. Jean (Environmental Solutions & Innovations, Inc), John L. Neff (Central Texas Melittological Institute), T'ai H. Roulston (University of Virginia), Laura Russo (University of Tennessee), Kimberly A. Stoner (Connecticut Agricultural Experiment Station), Michael Veit (freelance naturalist), and Keng-Lou James Hung (University of Oklahoma)Keng-Lou James Hung (University of Oklahoma) for comments and records.

Thank you for taxonomy and state attributions, John Ascher. Thanks for decriptions, authors: Robertson, Cresson, Smith, Viereck, Cockerell, Mitchell, Timberlake, Say, LaBerge, Crawford, Provancher, Patton, Swenk, Kirby, Lovell & Cockerell, Snelling & Stage, Dalla Torre, Ashmead, Atwood, Ribble, Fabricius, Deyrup & Deyrup, Hall & Ascher, Stevens, Lepeletier, Rightmyer, Deyrup, Ascher, & Griswold, and Sandhouse. We greatly appreciate the efforts of the BugGuide, Discover Life, Go Botany, and USDA-NRCS PLANTS Database groups to compile distribution and natural history information for bees and plants.

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