Chelostoma Latreille 1809

Key to Subgenera of Chelostoma

(modified from Griswold & Michener, 1998; Michener, 2007)

1. Third labial palpomere flatened, its axis a continuation of that of second palpomere; seventh metasomal tergum of male with dorsal pit.................... 2

—. Third labial palpomere not flatened, its axis directed laterally as in most megachilid bees; seventh metasomal tergum of male without dorsal pit (male unknown in Ceraheriades Tkalců)................................................................ 5

2(1). Preoccipital carina present (sharply angled medially in C. ventrale Schletterer but not carinate); propodeum with sloping basal zone litle more than one-half as long as metanotum; first metasomal tergum shallowly concave anteriorly [Palearctic]......................................................... Gyrodromella Michener

—. Preoccipital carina absent; propodeum with horizontal basal zone at least two-thirds as long as metanotum; first metasomal tergum with anterior surface convex except for longitudinal groove........................................................ 3

3(2). Parapsidal line half as long as tegula or more; second metasomal sternum of male without sloping platform, or, if present, then not carinate; labrum of female less than twice as long as broad (longer in C. isabellinum Warncke)..... 4

—. Parapsidal line less than half as long as tegula; second metasomal sternum of male with median prominence, its posterior surface a flat sloping platform margined by carina; labrum of female elongate, nearly 3× as long as broad or more (shorter in C. nasutum Pérez) [Palearctic, introduced into Nearctic]................................................................... Chelostoma Latreille, s.str.

4(3). Male seventh metasomal tergum without lateral processes (Fig. 6); setae of outer surface of probasitarsus pectinately branched to plumose (Fig. 4) [Palearctic].......................................................................... Foveosmia Warncke

—. Male seventh metasomal tergum with lateral processes (Fig. 5); setae of outer surface of probasitarsus simple (Fig. 3) [Nearctic].... Neochelostoma, n. subgen.

5(1). Metacoxa not carinate [Nearctic].............................. Prochelostoma Robertson

—. Metacoxa with longitudinal carina along inner ventral margin.................. 5

6(5). First metasomal tergum not concave on anterior surface; female mandible elongate, bidentate; labrum apically thickened [Central Asia].......................................................................................................................................... Ceraheriades Tkalců

—. First metasomal tergum shallowly concave on anterior surface; female mandible not elongate, tridentate; labrum not apically thickened [Himalayas to Thailand]............................................................................. Eochelostoma Griswold