Pollen Specialist Bees of the Western United States

Jarrod Fowler (2020)

Andrena helianthi

Andrena hirticincta

Melissodes desponsus

Svastra petulca

Introduction

This website compiles associations among native pollen specialist bees and native host plants from the Western 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

Visit:
Fowler, J. (2020). Pollen Specialist Bees of the Central United States
Fowler, J. & Droege, S. (2020). Pollen Specialist Bees of the Eastern United States

Pollen Specialist Bees

Roughly 35% of the ~3,000 species of bees native to the Western 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 Western United States potentially imperil native pollen specialist bee species and their endemic, 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 Discover Life (Ascher & Pickering 2020), peer reviewed articles (Bouseman & LaBerge 1978; Brooks & Griswold 1988; Cane 2018; Cockerell 1916, 1919; Cresson 1878; Daly 1973; Danforth 1994; Donovan 1977; Griswold 1993; Griswold & Miller 2010; Hurd et al. 1980; LaBerge 1963, 1967, 1969, 1971a, 1971b, 1973, 1977, 1980, 1985, 1986, 1989; LaBerge & Bouseman 1970; LaBerge & Ribble 1972, 1975; Lanham, 1981; Linsley & MacSwain 1958; McGinley 2003; Michener 1939; Michez & Eardley 2007; Minckley et al. 1994, 2000; Moldenke 1976, 1979; Parys et al. 2018; Portman, Neff, & Griswold 2016; Pow 2019; Provancher, 1895; Ribble 1974; Robertson 1926, 1928, 1929; Rozen 1958, 1992; Snelling 1983; Thorp 1969; Timberlake 1951, 1954, 1956, 1958, 1960, 1962, 1964, 1968, 1975, 1980; Wright 2018), technical bulletins (Danforth 1996; Grigarick & Stange 1968; Hurd & Michener 1955; Krombein et al. 1979; LaBerge 1967; Mitchell 1960, 1962; Ribble 1968; Stephen 1954; Thorp & LaBerge 2005; Timberlake 1953), and personal communications.

If bees and plants were indigenous to the Western 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 2020) and county-level distributions from The Biota of North America Program (Kartesz, BONAP 2015). This study includes only host plant genera that are native and documented as present in at least one county of at least one of the eleven regional states: Arizona, California, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington, and Wyoming. 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 Western United States were alphabetically tabulated with associated host plant families in Table 1. Six families, 11 subfamilies, 15 tribes, two subtribes, 53 genera, 125 subgenera, and 947 species of pollen specialist bees were listed. The bee family with the most pollen specialists was Andrenidae (564 spp.), while the most speciose subfamily was Panurginae (361 spp.), tribe was Panurgini (285 spp.), subtribe was Perditina (278 spp.), genus was Perdita (270 spp.), and subgenus was Perdita (171 spp.). The most recurrent authorities (n = 65 authors) were Theodore Dru Allison Cockerell (1866–1948, 258 spp.), Philip Hunter Timberlake (1883–1981, 244 spp.), Ezra Townsend Cresson (1838–1926, 85 spp.), and Wallace Edmund LaBerge (1927–2013, 44 spp.). Most species were first described during years 1878 (47 spp.), 1896 (44 spp.), and 1961 (40 spp.).

The states most inhabited by pollen specialist bees were: California (665 spp.; 44% spp.), Arizona (512 spp.; 49% spp.), New Mexico (423 spp.; 46% spp.), Utah (384 spp.; 41% spp.), Nevada (379 spp.; 45% spp.), Colorado (302 spp.; 32% spp.), Wyoming (193 spp.; 35% spp.), Oregon (190 spp.; 30% spp.), Idaho (189 spp.; 33% spp.), Washington (134 spp.; 27% spp.), and Montana (117 spp.; 31% spp.). Of the 947 species of pollen specialist bees, 172 spp. were recorded only in California, while 42 spp. were recorded in all 11 states. Overall, 560 bee species were considered "Rare", while 246 spp. were “Uncommon-Rare", 62 spp. were "Uncommon", 36 spp. were “Common-Uncommon", and 13 spp. were "Common". The months of activity for pollen specialist bees relative to associated host plant flowering phenology were May (454 spp.), August (435 spp.), June (426 spp.), April (393 spp.), July (381 spp.), September (331 spp.), March (208 spp.), October (124 spp.), February (27 spp.), November (23 spp.), December (6 spp.), and January (5 spp.). Oftentimes, pollen specialist bees had only three month (290 spp.) or two month (288 spp.) flight periods.

The most recurrent host plant families among pollen specialist bee species were Asteraceae (297 bee spp.) and Fabaceae (64 spp.). The top 50 most recurrent host plant genera (N = ~250) associated with pollen specialist bee species were: Helianthus L. (102 spp.), Gutierrezia Lag. (94 spp.), Ericameria Nutt. (93 spp.), Chrysothamnus Nutt. (91 spp.), Grindelia Willd. (84 spp.), Heterotheca Cass. (78 spp.), Verbesina L. (60 spp.), Solidago L. (59 spp.), Baileya Harv. & A. Gray ex A. Gray (48 spp.), Machaeranthera Nees (44 spp.), Erigeron L. (37 spp.), Phacelia Juss. (37 spp.), Camissonia Link (36 spp.), Encelia Adans. (36 spp.), Cirsium Mill. (35 spp.), Isocoma Nutt. (35 spp.), Symphyotrichum Nees (34 spp.), Dalea L. (31 spp.), Astragalus L. (29 spp.), Lotus L. (29 spp.), Senecio L. (29 spp.), Salix L. (28 spp.), Sphaeralcea A. St.-Hil. (28 spp.), Pectis L. (27 spp.), Baccharis L. (24 spp.), Coreopsis L. (23 spp.), Cryptantha Lehm. ex G. Don (23 spp.), Eriogonum Michx. (22 spp.), Prosopis L. (23 spp.), Psorothamnus Rydb. (22 spp.), Rudbeckia L. (22 spp.), Tiquilia Pers. (22 spp.), Chaenactis DC. (21 spp.), Euphorbia L. (21 spp.), Haplopappus Cass. (21 spp.), Mentzelia L. (20 spp.), Heliomeris Nutt. (19 spp.), Oenothera L. (18 spp.), Viguiera Kunth (18 spp.), Larrea Cav. (16 spp.), Lupinus L. (17 spp.), Stephanomeria Nutt. (16 spp.), Gaillardia Foug. (15 spp.), Lasthenia Cass. (14 spp.), Agoseris Raf. (13 spp.), Malacothrix DC. (13 spp.), Opuntia Mill. (13 spp.), Parkinsonia L. (13 spp.), Clarkia Pursh (12 spp.), and Nama L. (12 spp.).

Tables

Table 1. Pollen specialist bee families (n = 6), genera (n = 52), and species (n = 947) with taxonomic authorities, distributions according to records from 11 states (AZ, CA, CO, ID, MT, NM, NV, OR, UT, WA, and WY), regional conservation status (Common, Uncommon, or Rare), phenology according to records from 12 months, 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. 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):