Biosystematics of the Cleptoparasitic Bee Genus Epeolus Latreille and its Ecological and Evolutionary Relationship with Its Hosts of the Bee Genus Colletes Latreille

Cleptoparasitic (cuckoo) bees are those that appropriate food stores from bees in other genera for their own offspring. Upwards of 15% of all bees and 28% of the family Apidae are cleptoparasitic. Despite their taxonomic richness, not much is known about the evolutionary mechanisms responsible for generating the great diversity of cuckoo bees. Moreover, studies of their evolutionary history are complicated because for many genera existing taxon concepts are problematic and taxonomic expertise is lacking. Epeolus Latreille (Hymenoptera: Apidae) is a widespread genus of cuckoo bees specialized on polyester bees of the genus Colletes Latreille (Hymenoptera: Colletidae), and belongs to the subfamily Nomadinae, the largest taxon of cleptoparasitic bees. Since Epeolus exhibits high host specificity, the genus can potentially serve as a model for studying the effects of bee host evolution on cleptoparasite diversification. This would first require that the taxonomy of species in Epeolus, which has been problematic, be resolved. Since North America has more Epeolus spp. than any other continent, and since others have recently or simultaneously revised species from other regions, a major objective of the present study has been to revise the species occurring in Canada and the United States. As a result, a total of 43 valid species were confirmed as present in the region, of which 15 are newly described. Additionally, 19 redundant names are newly synonymized under those of seven valid species. The next major objective has been to construct dated phylogenies for Epeolus and associated Colletes based on molecular (and in the case of Epeolus also morphological) data. The Epeolus phylogeny includes 53 ingroup and 7 outgroup taxa, whereas the Colletes phylogeny includes 18 ingroup taxa (species known or presumed to be hosts of particular Epeolus species) and two outgroup taxa (other colletids). The findings suggest that Epeolus originated somewhere in the Holarctic, and both genera originated sometime in the Miocene (between 19 and 17 Ma). Although there is some phylogenetic congruence between the compared Colletes and Epeolus clades, more speciation events in Epeolus could be linked to existing or pre-existing physical barriers than to Colletes diversification.