Trigona

Engel, Michael S., Herhold, Hollister W., Davis, Steven R., Wang, Bo & Thomas, Jennifer C., 2021, Stingless bees in Miocene amber of southeastern China (Hymenoptera: Apidae), Journal of Melittology 2021 (105), pp. 1-83 : 74-78

Key to Subgenera of Trigona

(worker caste)

1. Mandible with four teeth .......................................................................................... 2

—. Mandible with five teeth ( Figs. 130, 147) ................................................................. 3

2(1). Labrum simple, surface gently and evenly convex; wings dichroic, proximally infuscate, apically whitish ( e.g., Fig. 136); pterostigma yellowish brown; scape black ........................................................................ Aphaneuropsis Engel , n. subgen.

—. Labrum bigibbous, with pronounced mediolongitudinal furrow ( e.g., Fig. 130); wings uniformly fuscous; pterostigma brown to dark brown; scape lighter ventrally, light brown to yellowish brown ................... Koilotrigona Engel , n. subgen.

3(1). Metatibia with distinct corbicula on apical prolateral surface (corbicular surface concave) ( Fig. 132), superior distal angle present ( Fig. 132), retromarginal fringe setae abundant ( Fig. 132) ................................................................................ 4

—. Metatibia without defined corbicula on apical prolateral surface (corbicular surface not concave) ( Fig. 131), superior distal margin rounded ( Fig. 131), retromarginal fringe setae less numerous ( Fig. 131) ..... Necrotrigona Engel , n. subgen.

4(3). Labrum simple, surface gently and evenly convex; vertex with distinct postocellar ridge ( Figs. 135, 138, 139, 144–148); integument entirely dark brown to black ( Figs. 133, 134, 138, 144, 145, 147) (except entirely orange in T. dallatorreana Friese ) ........................................................................................................................... 5

—. Labrum bigibbous, with mediolongitudinal furrow ( Fig. 130) (furrow somewhat weak in T. williana Friese ); vertex without postocellar ridge ( Fig. 129), or ridge quite weak; integument largely yellowish orange ( Figs. 128, 129) (head, mesoscutum, and parts of pleura sometimes largely black but clypeus and antenna always yellowish to yellowish orange) ............................... Aphaneura Gray

5(4). Wing membrane not as below, if slightly lighter apically, then transition gradual across wing length; metatibial width variable, sometimes comparatively narrow ............................................................................................................................... 6

—. Wing membrane strikingly dichroic, proximally darkly infuscate, apically whitish ( Figs. 133, 136); metatibia broad apically, with broadly rounded retromarginal contour ( Fig. 133) ......................................... Dichrotrigona Engel , n. subgen.

6(5). Small bees, head width 2.5 mm or less; forewing (including tegula) length less than 6.5 mm; metatibia narrow, retromarginal contour comparatively straight until apical fifth ........................................................................................................... 7

—. Larger bees, head width typically 2.5 mm or greater, rarely as small as 2.45 mm (in some T. corvina Cockerell ), forewing (including tegula) length 6.9 mm or greater; metatibia broader, typically with broadly rounded retromarginal contour ......................................................................................... Trigona Jurine , s.str.

7(6). Apical fundal surface of metatibia near corbicula with abundant minute, fine, appressed setae ( Figs. 140, 141); scape with prominent, thick, black bristles along length, such bristles often as long as scape diameter ( Figs. 145, 149); clypeus in profile with numerous, erect, black bristles; distance from median ocellus to postocellar ridge about ocellar diameter ( Fig. 146); smaller bees, intertegular distance 1.35 mm or less .......................................... Nostotrigona Engel , n. subgen.

—. Apical fundal surface of metatibia near corbicula with minute, fine, appressed setae either lacking or exceedingly sparse ( Figs. 142, 143); scape without thick bristles, with fine, lighter setae, such setae shorter than scape diameter ( Fig. 147, 150); clypeus in profile with a few short, fine setae, without black bristles; distance from median ocellus to postocellar ridge less than ocellar diameter ( Fig. 148); larger bees, interegular distance 1.4 mm or greater ................................ ......................................................................................... Ktinotrofia Engel , n. subgen.