Submitted to: Canadian Journal of Arthropod Identification
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/18/2011
Publication Date: 11/1/2011
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: 1-107. Interpretive Summary: Leafcutter bees are important pollinators of crops and native plants. They are a large group with diverse nesting habits; nest sites include holes in pithy stems or wood, existing cavities in old buildings, and holes in the ground. Leaf pieces and/or petals are used in nest construction. A study of the leafcutters of Canada and Alaska was conducted. DNA barcoding was used to determine the species in this taxonomically difficult group. As a result two subspecies are determined to be distinct species, two species thought to be restricted to North America are found to be the same as two European species, four supposed species are found to be merely color morphs of other named species, and three species previously unknown from Canada are reported. As a result 38 species are now known from Canada and Alaska. An illustrated key makes identifications of these species possible and will prove useful for states in the USA that border Canada. Nesting biologies are summarized in a table.
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.