Megachile (Xanthosarus) gemula Cresson, 1878

Megachile gemula Cresson, 1878: 118 . Mitchell 1927b: 178. Drons 2012: 58.

Megachile (Delomegachile) gemula Cresson; Mitchell 1935b: 181; 1936: 185; 1962: 134. Butler 1965: 6. Hurd 1979: 2059. Ivanochko 1979: 186.

Megachile (Xanthosarus) gemula; Raw 2002: 36. Scott et al. 2011: 56. Sheffield et al. 2011: 78. Reese et al. 2018: 23. Delphia et al. 2019b: 649. Sheffield and Heron 2019: 70.

Diagnosis. The female of M. gemula can be identified by white pubescence on T1–2 that contrasts with the dark pubescence on T3–5, reddish-brown to black scopal setae on S2–6, 4-toothed mandibles with a truncate basal tooth (Fig. 7E), and base of mandibles square-shaped (viewed laterally) with parallel sides for a distance as long as wide, then tapering apically (Fig. 6J). Females of M. gemula are most similar to M. melanophaea, which have mandibles gradually tapering in width towards apex (from a lateral view) (Fig. 6I) and orange scopal setae on S2–6. The male of M. gemula can be identified by its narrow, ventrally excavated probasitarsus, 4-toothed mandibles, and acute posterior angle of the dorsal face of the protibia, the apex entirely dark. The male of M. gemula is most similar to M. melanophaea, in which the dorsal face of the protibia has a rounded and spatulate posterior angle that is entirely cream to pale yellow at the apex.

Notes. Megachile gemula is found widely in Montana though, like many species, has not been extensively collected in eastern regions of the state (Fig. 1M). It is known to nest in poplar logs and hollow twigs (Sheffield et al. 2011). Photographs, a full morphological description, and notes on the biology of this species can be found in Sheffield et al. (2011).