Bombus suckleyi

Greene, 1860

Suckley's Cuckoo Bumble Bee, Suckley's Bumble Bee

suckleyi is a cuckoo (subgenus Psithyrus) and obligate of other Bombus . It lacks () on its hind legs, having lost the ability to collect pollen and nectar for its own . The species invades colonies, kills or subdues the resident , and manipulates host to provision its offspring. to northwestern North America, it has experienced severe declines of approximately 77% and is classified as critically endangered by the IUCN and NatureServe.

Bombus (Psithyrus) suckleyi by the Smithsonian. Used under a CC0 license.

Pronunciation

How to pronounce Bombus suckleyi: /ˈbɒmbəs ˈsʌk.li.aɪ/

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Identification

Distinguished from other cuckoo by the T4 with a central black ( bohemicus has T4 entirely yellow). Similar include Bombus insularis, Bombus flavidus, and Bombus bohemicus. Absence of separates all Psithyrus from non-parasitic Bombus subgenera. Males distinguished by convex hind legs with sparse hairs compared to female's densely hairy convex .

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Habitat

Western meadows across a wide range of elevations, particularly higher elevation meadows within forest or subalpine zones. Requires suitable colonies for , continuous floral resources through the growing season, and undisturbed sites for . Historically found in meadow-complexes interspersed with forests or in field margins and hedgerows within agricultural landscapes.

Distribution

Northwestern North America: Alaska, western and central Canada (all 10 provinces, with historic records concentrated in southern British Columbia, Alberta, and Saskatchewan plus a disjunct in Newfoundland), and 11 western United States. Current range severely reduced, with more than 50% of historic range lost.

Seasonality

Females active late May to late October in California, with peak activity in June. Males active early July to late September in California, with peaks in late July and early September. Females emerge later than to facilitate colony invasion.

Diet

forager. feed on nectar and pollen from diverse flowers, primarily Asteraceae (Aster, Chrysothamnus, Cirsium, Solidago) and some Fabaceae (Trifolium). Documented floral associations include Cirsium (15 observations), Aster sp. (11), Centaurea repens (10), and Trifolium sp. (4).

Host Associations

Bombus occidentalis - primary Western ; documented breeding
Bombus terricola - Recorded in colonies
Bombus rufocinctus - Recorded in colonies
Bombus fervidus - Recorded in colonies
Bombus nevadensis - Recorded in colonies
Bombus appositus - Recorded in colonies

Life Cycle

Obligate with no —all individuals are reproductively capable. Females emerge in spring, forage until locating suitable colony, then invade by killing or subduing resident . Host workers provision offspring. Developed individuals leave nest to mate. Mated females feed on nectar and pollen before in loose soil, leaf litter, or debris. Males die after mating. No independent colony founding; entirely dependent on host for rearing.

Behavior

Females locate and invade established colonies, using aggression to usurp the resident . Manipulates host through chemical or behavioral dominance to continue colony maintenance and larval provisioning. Forages for sustenance but does not collect resources for offspring. Exhibits delayed relative to host to ensure availability of established colonies for invasion.

Ecological Role

of wildflowers and through foraging. As an obligate , are tightly coupled to abundance. Declines indicate broader stress affecting . Contributes to of Asteraceae and Fabaceae species in meadow ecosystems.

Human Relevance

Subject of concern due to severe decline. Listed as critically endangered by IUCN and NatureServe (G1). Petitioned for U.S. protection in 2020. Listed under California Endangered Species Act as of June 2019. Declines attributed to collapse, , loss, competition from non- , climate change, and bombi exposure. Agricultural interests have opposed listing due to regulatory concerns.

Similar Taxa

Bombus bohemicusSimilar size and general appearance; distinguished by T4 being entirely rather than yellow with central black
Bombus insularisOverlapping range and cuckoo ; color pattern differences in abdominal tergites
Bombus flavidusSimilar parasitic lifestyle and subgenus Psithyrus; specific tergite coloration patterns differ

More Details

Conservation Status Details

NatureServe ranking G1 (critically imperiled) since 2018. IUCN critically endangered. Estimated 77% overall decline with relative abundance at less than 10% of historic levels. Designated of 'great need' in Washington, Idaho, Colorado, and California. Legal status in California confirmed after court challenge regarding protection under state .

Taxonomic Notes

Named after biologist George Suckley. Classified in subgenus Psithyrus along with all cuckoo . Recognized as valid by ITIS. First described by John Greene in 1860.