The male of Megachile nivalis Friese, with an updated key to members of the subgenus Megachile s. str. (Hymenoptera : Megachilidae) in North America

{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.}