Key to species of the genus Diochus of Bhutan, India, Nepal, Myanmar, Pakistan and Thailand (Figs 1−13)

1 Elytra uniformly colored, dark brown to yellowish brown..................................................... 2

- Elytra with basal part black, and apical part mostly reddish yellow (Fig. 13).......... Diochus bicoloripennis Coiffait, 1981

2 Antennomeres long, third antennomere 3−4 times longer than wide.............................................. 3

- Antennomeres short, third antennomere 1−2.5 times longer than wide............................................ 5

3 Elytra brown, distinctly lighter than pronotum; posterior margin of male sternite VIII emarginate medially, with numerous short setae in emargination (Figs 5-1E−L); aedeagus with a single hooked asymmetrical sclerite on top (Figs 5-1I−M)................................................................................................ D. setatus sp. nov.

- Elytra dark brown to black brown, about the same color as pronotum; posterior margin of male sternite VIII emarginate and either without setae in emargination or with numerous longer setae along entire apex; aedeagus with internal sclerites all symmetrical......................................................................................... 4

4 Pronotum elliptical, anterior region near anterior angles distinctly deflexed and narrowed; posterior margin of male sternite VIII emarginate medially, with numerous setae (Figs 9-1B−C, H); aedeagus with paired horn-like sclerites, parameres shorter (Figs 9-2A−D); spermatheca in basal part with widened tube (Figs 9-2A−D)................ D. conicollis (Motschulsky, 1858)

- Pronotum not elliptical; anterior region near anterior angles not so deflexed and narrowed; posterior margin of male sternite VIII emarginate medially, without setae in emargination (Figs 2-1E, J); aedeagus without paired horn-like sclerites, parameres longer (Figs 2-2 A−D); spermatheca in basal part with tube not widened (Figs 2-2 E−H).............. D. cameroni sp. nov.

5 Fore body reddish ochraceous; tempora markedly widened posteriad; lateral margins of pronotum nearly parallel (Figs 11 A−B; antennae shorter, antennomeres 6−10 slightly transverse................................ D. ochraceus Cameron, 1926

- Fore body dark brown to yellowish brown; lateral margins of pronotum slightly widened posteriad; antennae longer, antennomeres 6−10 not transverse........................................................................ 6

6 Anterior region of pronotum near anterior angles deflexed, lateral margins distinctly widened posteriad................. 7

- Anterior region of pronotum near anterior angles slightly deflexed, lateral margins slightly widened posteriad or nearly parallel............................................................................................. 8

7 Head elliptical (Figs 7-1A, E); male sternite VIII widely and shallowly emarginate medially with almost straight median part (Figs 7-1C, H); aedeagus elongate, slightly widened apically, parameres very short (Figs 7-1D, L−M). Female unknown...................................................................................... D. ceylonicus sp. nov.

- Head rounded oblong (Fig 8-1A); male sternite VIII triangularly emarginate medially; aedeagus elongate, narrowed apically, parameres longer (Figs 8-1I−J)....................................... D. guizhouensis Shuai, Nozaki & Tang, 2021

8 Head markedly elongate (Figs 6-1 A, D); male sternite VIII widely, shallowly and triangularly emarginate; aedeagus with paired horn-like sclerites and helical structures (Figs 6-2A−D); spermatheca with basal part of tube narrow (Figs 6-2E−F)...................................................................................... D. keralanus sp. nov.

- Head slightly elongate; male sternite VIII, aedeagus and spermatheca different..................................... 9

9 Body small, head without elevation between eyes in male (Figs 12-1A, E); male sternite VIII very long, slightly emarginate apically (Figs 12-1C−D, I), aedeagus with transverse sclerite on top and irregular sclerites in middle (Figs 12-2A−D), spermatheca apically with a loop (Figs 12-2E−G)................................. D. antennatus (Motschulsky, 1858)

- Body large, head with elevation between eyes in male; male sternite VIII shorter; aedeagus without transverse sclerite, spermatheca different, without circle apically.............................................................. 10

10 Posterior margin of male sternite VIII without setae, roundly emarginate (Figs 10-1C−D), aedeagus narrowed apically, parameres longer nearly as long as median lobe (Figs 10-1E−G); spermatheca with short tube, with only one bend (Figs 10-2C−E)........................................................................... D. punctipennis (Motschulsky, 1858)

- Posterior margin of male sternite VIII with setae; aedeagus not or less narrowed apically, parameres shorter, much shorter than median lobe; spermatheca different, tube longer, with more bends.............................................. 11

11 Posterior margin of male sternite VIII with fascicular setae on both sides (Fig 3-1E); aedeagus with parameres thicker and shorter (Figs 3-1 I−J)................................................................. D. emarginatus sp. nov.

- Posterior margin of male sternite VIII with only normal setae on both sides (Fig 4-1E); aedeagus with parameres thinner and longer (Figs 4-1I−J)...................................................................... D. setifer sp. nov.