Poorly known eastern bumble bees
In a recent posting by Sam on the bees of Wisconsin, he drew attention to issues surrounding the identification of some surprisingly poorly known bumble bees of eastern North America. From the material available at present, there may be problems with some of the published keys –
This small bumble bee seems (at the least) to have been under-recorded. It can be recognized most easily by the shape of the oculo-malar area, which is approximately as long as broad, or just shorter than broad, depending on how it is measured. Part of the confusion has probably been that this species is very variable in color pattern, e.g. for queens and workers: (1) the pile of the head varies from yellow to black; (2) the pile of the thorax varies from predominantly yellow, to having a black spot between the wing bases, to having a black band between the wing bases; and (3) the pile of T5 varies from black (like B. vagans), to yellow, to white (but never orange).
This species often looks superficially very similar to B. sandersoni, but the oculo-malar area is longer than broad. Females have the pile of T5 black, except in the far north east of its range (Newfoundland), where it is yellow (described under the name bolsteri, which also has particularly many black hairs intermixed with the yellow on the thoracic dorsum).
This species has also been confused with B. sandersoni. B. frigidus is less common in the east of North America than it is in the west. In the east, it occurs as far south as just inside the US border, at least in Wisconsin (Wolf & Ascher, 2009). Females have a black band between the wing bases and the pile on the posterior of T4 and on T5 is orange-red, sometimes quite bright.
All three species show other more subtle differences, especially in the penis valve of the male genitalia.
It would be great to get eastern US specimens of B. frigidus barcoded, along with more B. sandersoni. Our preliminary barcoding results in BEE-BOL projects have been very encouraging in supporting the interpretation above based on morphology. But more specimens are needed!