Appearance
Like all cuckoo bumble bees, the outer tibial surface of the hind leg is convex and densely hairy, rather than adapted for pollen transport. Their heads are more teardrop shaped and the thorax is predominantly yellow including the lower sides and sometimes down to segment T4 or 5. Hair on the face is usually black with some yellow hairs, there are usually no black hairs on the thorax and would not form a band between the wing bases. Metastomal hairs are short and even and longer on T5 than the other joints and matte with dense punctures on T6. The wings are slightly opaque ranging from a reddish brown to brownish black and yellowish during pubescence. They are sometimes interspersed with black hairs. The male genitalia contain some of the most distinguishing characteristics when differentiating bumble bee species. The gonostylus are lined with long hairs, hairs on the yellow volsella are much shorter. The penis valve is long and thin and relatively straight compared to other bumble bee species.Distribution
Found in parts of the Northeastern area of North America. Their distribution includes eastern to central parts of Canada, Northeastern U.S states and parts of the mid-western and southeast regions of the U.S.Habitat
When invading a colony, "P. citrinus" acquire the host scent as well as transfer it using mauling to camouflage and dominate the colony. Colony recognition cues within a colony have an important function in cooperation and distinguishing between nestmates and non-nestmates, parasites, and robbers. Many species in the subgenus "Psithyrus" use scent to evade the host colony's recognition cues. Long chain alkanes and alkenes may possibly play a role in the production of "Psithyrus"’ scent. The Dufour's gland is enlarged in the "Psithyrus" subgenus and believed to be the source of chemical production for bees in the genus.References:
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