J. HYM. RES. Vol. 16(1), 2007, pp. 178-191 The Male of Megachile nivalis Friese, with an Updated Key to Members of the Subgenus Megachile s. str. (Hymenoptera: Megachilidae) in North America Cory S. Sheffield and Sue M. Westby (CSS) Department of Biology, York University, 4700 Keele Street, Toronto, ON Canada M3J 1P3 email:
[email protected] (SMW) Agriculture and Agri-Food Canada, 32 Main Street, Kentville, NS, Canada B4N 1J5 Abstract. — The previously unknown male of Megachile nivalis Friese is described. Males of this species are very similar to those of M. relativa Cresson and because of geographic overlap of the two species, many male specimens presently identified as M. relativa within collections may actually be M. nivalis. An identification key and illustrations of mandibles are provided for females and males of the subgenus Megachile s. str. of North America. Images of genitalia, selected sterna, the lower genal area, clypeus, and forewings for males of both M. relativa and M. nivalis are also provided for comparison and to facilitate differentiation of the two species. A tabular summary is also provided for species of Megachile in North America that are known from only one sex to encourage the search for possible additional synonyms or hitherto unknown sexes. Key words. — Apoidea, Megachilidae, Megachile (Megachile), Megachile nivalis, male description, North America Leafcutter and mason bees of the genus Megachile Latreille (Hymenoptera: Mega-chilidae) are a common and diverse group (Mitchell 1980, O'Toole and Raw 1991, Michener et al. 1994, Baker and Engel 2006) whose members display many mor-phological and behavioral adaptations (Michener 2000). Currently, 55 extant sub-genera are recognized (Baker and Engel 2006), 30 of which are known from the western Hemisphere. In North America, thirteen subgenera are indigenous, but an additional three have been introduced (Michener 2000, Cane 2003). Hurd (in Krombein et al. 1979) listed 134 species of Megachile in North America north of Mexico (including the genus Oialicodoma); Michener et al. (1994) indicate 139 species. Since the publication of Krombein et al. (1979), at least 111 of the cataloged North American species have undergone changes in subgeneric allocation (Raw 2002), and Raw (2004) indicates that the 519 described species of Megachile in the Western Hemi-sphere are now allocated to their proper subgenus. Much is known about the biology of many leafcutter bees due to their impor-tance in crop pollination (Pengelly 1955, Osgood 1974, Ivanochko 1979, Peterson et al. 1992, Free 1993, Richards 1993, Dela-plane and Mayer 2000, Raw 2002) and the fact that many species accept trap-nests (Medler 1959, 1964, Fye 1965, Krombein 1967, Frolich and Parker 1983, O'Toole and Raw 1991). Most members of the genus nest above ground in pre-existing cavities or excavate into pithy stems or decompos-ing wood (Stephen 1956, Ivanochko 1979). Trap-nesting of bees allows detailed study of life-history, nest building, provisioning and egg laying behaviors (Medler 1959, 1964, Klostermeyer and Gerber 1969, Fro-lich and Parker 1983, Kim 1992), and
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