Revisiting the subspecies conundrum of the bumble bee Bombus bifarius Cresson (Hymenoptera: Apidae) in North America

Among bumble bee (Bombus Latreille) taxonomists, Bombus bifarius Cresson is recognized as a highly variable species across its geographic distribution. Like many of the 250 species of bumble bee, B. bifarius is a taxonomic enigma, primarily due to the fact that taxonomic diagnosis of populations within the species is limited to variability in pubescence color patterns. Currently two subspecies of B. bifarius are recognized- B. bifarius subsp. bifarius and B. bifarius subsp. nearcticus. Delineation between the two subspecies rest primarily on the pubescence color patterns of the basal terga of metasoma. Historically, several other subspecies of B. bifarius were recognized, and are also diagnosed using pubescence color variation and geographic distribution. We revisit the subspecies conundrum of B. bifarius by using a combination of morphological characteristics (e.g. wing length, wing venation and malar space), pubescence color patterns, molecular markers and geographic distribution in a multivariate analysis to assess possible subspecific differences. The methods we employ are similar to those used to differentiate subspecies of honey bees (Apis mellifera Linnaeus). We discuss the relationship between the geographic distribution of color patterns of B. bifarius and the associated morphological and molecular correlates; as well as the evolutionary and practical importance of recognizing more than two subspecies of B. bifarius.