Submitted to: Canadian Journal of Arthropod Identification
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/18/2011
Publication Date: 11/29/2011
Citation: Sheffield, C.S., Ratti, C., Packer, L., Griswold, T.L. 2011. Leafcutter and mason bees of the genus Megachile Latreille (Hymenoptera: Megachilidae) in Canada and Alaska. Canadian Journal of Arthropod Identification. 18: 1-106. Interpretive Summary: The leafcutter and mason bees (genus Megachile) are important in their role as pollinators of crops and native flowering plants. They have realized and potential value as manageable pollinators on such crops as alfalfa and sunflowers. Until now it has been difficult to identify which of the many species of Megachile are visiting crops of interest. An illustrated key makes such identifications possible for the 38 species found in Canada and Alaska. The key will also prove useful for states in the USA that border Canada. Distributional maps are provided for each species. Nesting biologies are summarized in a table. Clarifications are made on the correct names for species. Using DNA techniques two species thought to be restricted to North America are found to be the same as two European species. Similarly several “species” that differ in color patterns are found to be the same species.
Technical Abstract: Leafcutter and mason bees of the genus Megachile are common members of the North American bee fauna and many Megachile species are important pollinators of summer flowering crops and native plant species. Despite this, no comprehensive account of species in Canada and Alaska has been published. Our objective is to provide an up-to-date revision of the genus Megachile of this region, including an interactive key to the species, and summaries of biogeographic distribution and life history. Additionally, divergence in a 658 bp segment of the mitochondrial COI gene (the “DNA barcode” region) was used to clarify the taxonomic status of several Megachile species in North America. Based on morphological differences and over 6% sequence divergence in COI, M. (Litomegachile) onobrychidis Cockerell, previously considered a subspecies of M. (Litomegachile) brevis Say, is recognized here as a valid species. Similarly, M. (Litomegachile) pseudobrevis Mitchell, found in the southeastern United States, is also considered a distinct species and removed from synonymy with M. brevis. Megachile (Eutricharaea) apicalis Spinola, M. (Megachiloides) casadae Cockerell and M. (Megachiloides) umatillensis (Mitchell) are recorded from Canada for the first time; M. (Xanthosarus) giliae Cockerell and M. (Megachile) nivalis are placed into synonymy with M. (Xanthosarus) circumcincta (Kirby) and M. (Megachile) lapponica Thomson, respectively, and are thus considered Holarctic in distribution; M. subanograe Mitchell is placed into synonymy with M. sublaurita Mitchell (previously only known from its melanistic female form), and the male is described for the first time. Megachile (Megachiloides) alamosana Mitchell, known only from the male, M. (Megachiloides) laurita Mitchell, and M. (Megachiloides) laurita semilaurita Mitchell (both melanistic female forms) are placed into synonymy with M. (Megachiloides) anograe Cockerell, the latter three species previously only known only from the females. Full descriptions of all 38 species found in Canada and Alaska are provided.