Key to Vietnamese species of Psyttalia Walker

1 Vein m-cu of fore wing angled with vein 2-CU1 and straight (Figs 4H, 8H, 14I); first subdiscal cell of fore wing parallel-sided; vein r of fore wing nearly linear with vein 3-SR (Figs 4H, 8H, 14I).............................................. 2

- Vein m-cu of fore wing gradually merging into vein 2-CU1 and more or less curved (Figs 2I, 6I, 10H, 12H, 16E); first subdiscal cell of fore wing distinctly widened posteriorly; vein r of fore wing weakly angled with vein 3-SR (Figs 2I, 6I, 10H, 12H, 16E)............................................................................................... 4

2 Body tricoloured (head and mesosoma brownish yellow, metasoma black but apex white); antenna with about 49 segments; clypeus triangular (Fig. 14B); pale yellowish hind femur strongly contrasting with black hind tibia (Fig. 13); pterostigma blackish brown (Fig. 14I)............................................................... P. tricolorata sp. nov.

- Body uni- or bicoloured, yellowish and at most with dark brown pattern; antenna with 33–36 antennomeres; clypeus transverse (Figs 4B, 8A); yellowish hind femur weakly contrasting with partly brown hind tibia (Figs 3, 7) or similarly coloured; pterostigma yellowish or brown (Figs 4H, 8H).............................................................. 3

3 Basal half of pterostigma and apical half of hind tibia brown; clypeus convex ventrally, resulting in a smaller hypoclypeal depression (Fig. 8B); scutellar sulcus parallel-sided (Fig. 8D); metasoma with dark brown pattern (Fig. 8E)................................................................................................ P. nigristriata sp. nov.

- Basal half of pterostigma and apical half of hind tibia yellow; clypeus straight ventrally, resulting in large hypoclypeal depresion (Fig. 4B); scutellar sulcus distinctly concave medio-posteriorly (Fig. 4D); metasoma without dark brown pattern (Fig. 4F).................................................................................. P. hoabinhensis sp. nov.

4 Strongly widened vein 1-CU1 of fore wing curved and 0.6 × as long as vein 2-CU1 (Fig. 16E); vein 1-SR of fore wing about as long as wide (Fig. 16E); vein r 0.3 × as long as vein 2-SR........................ P. latinervis Wu & van Achterberg

- More or less widened vein 1-CU1 of fore wing straight and 0.1 × as long as vein 2-CU1 (Figs 2I, 6I, 10H) or vein cu-a subinterstitial or antefurcal (Figs 2I, 12H); vein 1-SR of fore wing longer than wide (Fig. 2I); vein r 0.4–1.0 × as long as vein 2-SR (Figs 2I, 6I, 10H, 12H)............................................................................ 5

5 Vein m-cu of fore wing straight or nearly so (Fig. 15E); vein 2-SR+M of fore wing narrow (Fig. 15E); vein 1-SR of fore wing linear with vein 1-M..................................................................... P. incisi (Silvestri)

- Vein m-cu of fore wing more or less curved (Figs 2I, 6I, 10H); vein 2-SR+M of fore wing widened (Figs 2I, 6I, 10H); vein 1-SR of fore wing linear with vein 1-M more or less angled with vein 1-M............................................ 6

6 Vein cu-a of fore wing distinctly antefurcal (Fig. 2I); apical third of pterostigma paler than dark brown middle third; vein 1-SR of fore wing distinctly angled with vein 1-M; vein 2-SR of fore wing slightly widened medially (Fig. 2I); vein r of fore wing emitted distinctly before middle of pterostigma, and 0.4 × as long as vein 2-SR.................... P. antenervis sp. nov.

- Vein cu-a of fore wing postfurcal (Figs 6I, 12H) or subinterstitial (Fig. 10H); apical third of pterostigma as dark as brown middle third or nearly so; vein 1-SR of fore wing less angled with vein 1-M; vein 2-SR of fore wing narrow medially (Figs 6I, 10H, 12H); vein r of fore wing emitted more or less after middle of pterostigma, and 0.6-1.0 × as long as vein 2-SR....... 7

7 Pterostigma broad triangular in shape, and 3.1 × as long as wide medially (Fig. 10H); posterior half vein m-cu of fore wing about at level of vein 2-CU1 (Fig. 10H); vein 2-SR+M of fore wing strongly widened [vein r of fore wing 0.9 × as long as vein 2-SR]........................................................................... P. quadrinervis sp. nov.

- Pterostigma narrow triangular in shape, and 3.6–4.4 × (Figs 16I, 12H); posterior half of vein m-cu of fore wing distinctly above level of vein 2-CU1 (Figs 6I, 12H); vein 2-SR+M of fore wing less widened (Figs 16I, 12H) [vein r of fore wing 0.6–0.9 × as long as vein 2-SR].................................................................................... 8

8 Vein r of fore wing about 0.6 × as long as vein 2-SR (Fig. 12H); vein 2-CU1 distinctly curved that first subdiscal cell more widened medially (Fig. 12H); length of first tergite 1.25 × its apical width, dorsal carinae present in basal 0.5 of the tergite (Fig. 12I).................................................................................... P. sonla sp. nov.

- Vein r of fore wing 0.8–1.0 × as long as vein 2-SR (Fig. 6I); vein 2-CU1 weakly curved that first subdiscal cell less widened medially (Fig. 6I); length of first tergite 1.1 × its apical width, dorsal carinae present in basal 0.7 of the tergite (Figs 6G, H).................................................................................... P. mangiferae sp. nov.