Polistella Ashmead 1904

Key to the Vietnamese species of the subgenus Polistella

The characters used are applicable to both sexes unless the sex is specified. Polistes nipponensis is not included here as the species from Vietnam identified under this name is under investigation based on DNA data (personal information).

1. Hind wing with jugal lobe reduced, ocelli approximated with POD more or less equal to Od (Fig. 12); metasomal segment 1 narrowed, narrower than metasomal segment 2 (Fig. 14)........................................... 2

- Hind wing with jugal lobe not reduced, round, ocelli normal with POD much larger than Od (Fig. 13); metasomal segment 1 wider, about as wide as metasomal segment 2 (Fig. 15)............................................ 7

2. Fore wing with subapical fuscous cloud (Figs 16)...................................................... 3

- Fore wing without subapical fuscous cloud (Fig. 17)................................................... 5

3. Clypeus higher than wide, 1.1× as long as wide; inner eye margins 1.1× far apart from each other at vertex than at clypeus in frontal view (Figs 18); body with strong punctures. Body reddish-brown with prominent black mark (Fig. 47, 48)......................................................................................... 4

- Clypeus as high as wide; inner eye margins about as far apart from each other at vertex as at clypeus in frontal view (Fig. 19); body with weak punctures. Body reddish-brown with prominent yellow bands or marks (Fig. 49) P. nigritarsis Cameron

4. Propodeum with weak transverse striae, metasomal tergum 1 proportionally longer, 1.2× as long as its apical width, mesoscutum as long as wide between tegulae................................ P. adsimilis Nguyen & Carpenter

- Propodeum with strong transverse striae, metasomal tergum 1 proportionally shorter, less than 1.2× as long as its apical width, mesoscutum wider than long............................................. P. delhiensis Das & Gupta

5. Metasomal tergum 1 sharply angled at base (Figs 20), rather long, equal to or less than 1.2× as long as its apical width. Body dark brown or yellow....................................................................... 6

- Metasomal tergum 1 gradually swollen from base to apical margin (Fig. 21), very long, 1.4× as long as its apical width. Body yellow with prominent black mark (Fig. 50)............................. P. meadeanus (von Schulthess).

6. Propodeum with strong striae; body with coarse punctures; wing dark brown. Body reddish-brown with black marks (Fig. 51).................................................................................................................................................................. P. khasianus Cameron

- Propodeum with weaker striae; body with less strong punctures; wing transparent. Body yellow (Fig. 52)...................................................................................... P. pallidus Guisenleitner

7. Metasomal sternum 2 gradually swollen posteriorly, in lateral view with ventral margin weakly and smoothly curved (Fig. 22).................................................................................................................................................................................. 8

- Metasomal sternum 2 basally strongly swollen, in lateral view bulging anteriorly (Fig. 23)..................... 15

8. Medium-sized wasps; fore wing length 10.5¯ 14.5 mm. Marginal cell of fore wing with dark spot at apex........... 9

- Large-sized wasps; fore wing length 15.5¯ 18mm. Marginal cell of fore wing without dark spot................. 12

9. Body with strong punctures (Fig. 24). Propodeum with strong transverse striae. Body with yellow markings reduced, clypeus entirely or largely brown or black (Fig. 53, 54)................................................ 10

- Body with weaker punctures (Fig. 25). Propodeum with weaker transverse striae. Body with extensive yellow or reddish marks (Fig. 55, 56)............................................................................ 11

10. Female: Flagellomere 1 2.8 times as long as its maximum width. Frons and mesoscutum with less coarse punctures. Body mainly brown (Fig. 53).......................................... Polistes brunus Nguyen & Carpenter

- Female: Flagellomere 1 3 times or slightly greater than 3 times as long as its maximum width. Frons and mesoscutum with coarse punctures. Body mainly black with brown marks (Fig. 54).. Polistes communalis Nguyen, Vu & Carpenter

11. Tergum 4 without apical yellow band. Sternum 2 with posterlateral spots & 3 with narrow apical yellow band (Fig. 55)................................................................... Polistes stigma stigma (Fabricius)

- Tergum 4 with apical broad yellow band. Sternum 2–4 with very broad apical yellow bands (Fig. 56)................................................................................ Polistes stigma tamulus (Fabricius)

12. Pronotum with strong striation (Fig. 26, 27) Female metasomal sternum without longitudinal ridges (Fig. 29)...... 13

- Pronotum with weak striation (Fig. 28) or striation absent. Female metasomal sternum 4 medially with paired longitudinal ridges (Fig. 30)............................................................................ 14

13. Pronotal striation somewhat irregular (Fig. 26), spaces between striae densely and distincly punctured. Dorsal surface of pronotum smoothly curved down to the lateral surface. Male metasomal sternum VII without tubercle. Clypeus, mesoscutum, metasomal segments 3̅6 entirely black (Fig. 57)....................... P. sagittarius de Saussure

- Pronotal striation regular and very strong (Fig. 27). Border between dorsal and lateral surfaces of pronotum distinctly angled. Male metasomal sternum 7 with weak tubercle. Clypeus, mesoscutum, metasomal segments 2̅6 entirely brown (Fig. 58).................................................................................................................................................................. P. strigosus Bequaert

14. Pronotum with dense, coarse punctures, their edges forming reticulation (Fig. 28). Disc of scutellum convex. Metasomal sternum 2 in lateral view convex ventrally in anterior half. Anterior margin of male clypeus nearly straight (Fig. 31). Metasomal terga brown, with some black marks (Fig. 58). Wings transparent......... P. brunetus Nguyen & Kojima

- Pronotum with sparse, small punctures. Disc of scutellum hardly convex. Metasomal sternum 2 in lateral view weakly convex ventrally in the anterior two thirds. Anterior margin of male clypeus rounded (Fig. 32). Metasomal terga yellow with dark brown and/or black bands (Fig. 59). Wings infuscate........................ P. japonicus de Saussure

15. Marginal cell of forewing with dark spot. Metasomal terga entirely black (Fig. 60)......... P. horrendus Gusenleitner

- Marginal cell of forewing without dark spot. Metasomal terga black with yellow band........................ 16

16. Disc of scutellum flat, in profile smoothly passing from dorsal margin of mesoscutum (Fig. 33). Punctures on vertex, gena and metasomal terga fine, clathrate............................................................ 17

- Disc of scutellum convex (Fig. 34). Punctures on vertex and gena very coarse, larger than their interstices; punctures on terga coarse.................................................................................. 18

17. Propodeum shallowly excavated medially. Metasomal sternum 2 in lateral view strongly swollen ventrally in anterior one-third (Fig. 23). Male clypeus as wide as high with apical margin slightly produced, broadly rounded (Fig. 35). Scutellum black; propodeum with large lateral yellow spots (Fig. 61).................... P. dawnae Dover & Rao

- Propodeum deeply excavated medially. Metasomal sternum 2 in lateral view strongly swollen ventrally in anterior half to two-third. Male clypeus wider than high with apical margin hardly produced, very wekly rounded (Fig. 36). Scutellum brown; propodeum with small lateral yellow spots (Fig. 62)............... P. clandestinus Nguyen, Saito & Kojima

18. Propodeum with border between posterior and lateral faces bluntly angled.................................. 19

- Propodeum with border between posterior and lateral faces not angled..................................... 21

19. Female clypeus with very coarse puncture at based half, space between punctures less than puncture diameter (Fig. 37). Metasomal tergum 1 thick, in lateral view abruptly swollen dorsally just behind basal slit for reception of propodeal suspensory ligament, then weakly convex dosally after broadly rounded corner between anterior and dorsal faces. Metasomal sternum 2 in lateral view with anteroventral corner bluntly angled (Fig. 38), with hypothetical angle formed by anterior and ventral faces in nearly right-angle. Punctures on body surface very coarse and dense; dorsal metapleuron with punctures. Metasomal terga black (Fig. 63)........................ P. curcipunctum Nguyen, Saito & Kojima

- Female clypeus with less coarse and sparser punctures, space between punctures greater than puncture diameter. Metasomal tergum 1 not thick, in lateral view abruptly swollen dorsally just behind basal slit for reception of propodeal suspensory ligament, then bluntly angled into slightly or barely convex dorsal margin. Metasomal sternum 2 in lateral view with anteroventral corner sharply angled (Fig. 39) or slightly produced anteriorly (Fig. 40). Punctures on body surface less coarse and sparser; dorsal metapleuron without punctures. Metasomal terga black, with orange-yellow apical bands (Fig. 64, 65)............................................................................ 20

20. Medium-sized, robust wasp; fore wing length 11–13.5 mm. Female clypeus in lateral view convex, passing into slightly concave supraclypeal area. Punctures on vertex strong; those on pronotum, scutum, scutellum and metanotum coarse. Metasomal sternum 2 in lateral view with anteroventral corner slightly produced anteriorly (Fig. 39). Pair lateral yellow spots on metanotum absent (Fig. 64).................................................. P. lepcha Cameron

- Small-sized, robust wasp; fore wing length 9–10 mm. Female clypeus in lateral view weakly convex, smoothly passing into supraclypeal area. Punctures on vertex weaker; those on pronotum, scutum, scutellum and metanotum strong, less coarse. Metasomal sternum 2 in lateral view with anteroventral corner angled, not produced anteriorly (Fig. 40). Pair lateral yellow spots on metanotum present (Fig. 65)........................... P. gilvus Nguyen, Saito & Kojima

21. Female head higher than wide (Fig. 41). Dorsal metapleuron smooth, without punctures....................... 22

- Female head as wide as high as or wider than high (Fig. 42). Dorsal metapleuron punctured.................... 23

22. Propodeum with weak striation. Disc of scutellum strongly and evenly convex, in profile strongly raised above level of mesoscutum. Vertex, scutellum and propodeum black.......................... P. paco Nguyen, Saito & Kojima

- Propodeum with strong striation. Disc of scutellum slightly convex, in profile weakly raised above the level of mesoscutum. Vertex, scutellum and propodeum brown (Fig. 66).............................. P. santoshae Das & Gupta

23. Female clypeus as wide as high (Fig. 1)............................................................ 24

- Female clypeus wider than high (Fig. 42)........................................................... 26

24. Female clypeus with dense, fine pubescence in dorsal half. Male clypeus wider than high. Body brown with yellow apical margin on metasomal segments (Fig. 67)...................................... P. mandarinus de Saussure

- Female clypeus with dense, fine pubescence restricted to dorsal one third. Male clypeus as wide as high.......... 25

25. Male gena in lateral view 0.5 × as wide as eye (Fig. 3). Female flagellomere 4–6 wider than long. Sternum 2 in lateral view swollen ventrally in anterior half (Fig. 4). Metasomal segments 2–5 reddish-brown (Fig. 11)... P. chuyangsin, sp. nov.

- Male gena in lateral view 0.3 × as wide as eye (Fig. 43). Female flagellomere 4–6 as wide as long. Sternum 2 in lateral view swollen ventrally in anterior one-third. Metasomal segments 2–5 black with reddish-brown apical margin (Fig. 68)............................................................................ P. affinis Gusenleitner

26. Small, medium-robust wasp; fore wing length 11–12mm. Disc of scutellum convex. Punctures on abdomen small and not strong. Clypeus in lateral view prominently swollen anteriorly in upper one-third. Metasomal sternum 2 in profile swollen posteriorly in anterior half (Fig. 44). Metasomal terga black, with yellow apical bands (Fig. 44)........................................................................ P. reliciniclypeus Nguyen, Saito & Kojima

- Small, medium-robust wasp; fore wing length 13–14mm. Disc of scutellum almost flat. Punctures on abdomen larger and strong. Clypeus in lateral view swollen anteriorly at middle. Metasomal sternum 2 in profile swollen posteriorly in anterior one-third (Fig. 45). Metasomal terga black, with yellow apical band only on tergum 1 (sometimes absent) (Fig. 69).......................................................................................... P. nigerrimus Gusenleitner