Review of the bee subgenus Lasioglossum (Hemihalictus) in western North America (Hymenoptera: Halictidae)

Sweat bees in the cosmopolitan genus Lasioglossum are some of the most diverse and commonly collected bees in terrestrial ecosystems. The bee subgenus Lasioglossum (Hemihalictus) has never been reviewed in western North America. A taxonomic study was conducted to assess the status and validity of species in this region. Twenty-two species of L. (Hemihalictus) are treated, five of which are described as new: L. angusticulum sp. nov., L. engleri sp. nov., L. opata sp. nov., L. pathiranae sp. nov., and L. tomentosum sp. nov. Linear discriminant analysis and partitioning around medioids were used to test species limits in the L. arizonense species complex. Lasioglossum vanduzeei (Sandhouse & Cockerell, 1924) stat. rev. is resurrected from synonymy with L. arizonense (Crawford, 1907). Two Palaearctic species are documented in North America: L. villosulum (Kirby, 1802) and L. buccale (Pérez, 1903). The male of L. subobscurum (Cockerell, 1895) is described for the first time. Additionally, several taxonomic synonymies are proposed: L. aspilurus (Cockerell, 1925) is recognized as a senior subjective synonym of L. humboldtense (Michener, 1936); within the L. nitidiusculum species group, L. diatretum (Vachal, 1904) is recognized as a senior subjective synonym of L. supranitens (Cockerell, 1919); L. ruficorne (Crawford, 1907) is considered a senior subjective synonym of L. vaporellum (Cockerell, 1910) and L. pulveris (Cockerell, 1930); and L. synthyridis (Cockerell, 1906) is considered a senior subjective synonym of L. inconditum (Cockerell, 1916). Updated keys to species are provided for the L. (Hemihalictus) bees of North America north of Mexico.