Chelostoma, Latreille, 1809

Engel, Michael S. & Griswold, Terry, 2019, On the classification of North American Chelostoma (Hymenoptera: Megachilidae), Journal of Melittology 2019 (90), pp. 1-6 : 3-5

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

Figures

Figures 5–6. Male characters of Neochelostoma, new subgenus, and Foveosmia Warncke. 5. Seventh tergum of Chelostoma(Neochelostoma) tetramerum Michener, arrows indicate lateral projections. 6. Sev- enth tergum of C. (Foveosmia) distinctum (Stoeckhert).

Figures 3–4. Female characters of Neochelostoma, new subgenus, and Foveosmia Warncke. 3. Probasitarsus of Chelostoma (Neochelostoma) californicum Cresson. 4. Probasitarsus of C. (Foveosmia) campanularum (Kirby).