Key to the 18 known species of Ooctonus from China based on females

1 Metanotum and propodeum (Fig. 7; Triapitsyn 2010, p. 19, fig. 11) with reticulate sculpture........ O. hemipterus Haliday

- Metanotum and propodeum without reticulate sculpture....................................................... 2

2 Midlobe of mesoscutum with narrow median groove (Fig. 22; Huber 2010, p. 84, fig. 103)........................... 3

- Midlobe of mesoscutum without median groove (Figs 2, 11, 15)................................................ 9

3 Propodeum without median areole (Jin 2019 & Li 2020, p. 3, fig. 1e)............................ O. exsertus Jin & Li

- Propodeum with median areole (Fig. 22)................................................................... 4

4 Body almost entirely black, except eyes and ocelli dirty pink and gaster dark brown to black; ovipositor not exserted beyond apex of gaster...................................................................... O. sinensis Subba Rao

- Body brown to dark brown; ovipositor slightly or notably exserted beyond apex of gaster............................ 5

5 F5 and F6 without mps................................................................. O. saturn Triapitsyn

- F5 and F6 with 1 or 2 mps.............................................................................. 6

6 Funicle with F2 the longest and F8 the shortest; ovipositor exserted beyond apex of gaster by at least 0.18× its own length..................................................................................... O. kokozai Triapitsyn

- Funicle with all segments more or less subequal in length; ovipositor exserted beyond apex of gaster by at most 0.1× its own length.............................................................................................. 7

7 Propodeum with lateral carina split anteriorly (Fig. 22), forming a broadly Y-shaped carina not extending to anterior margin on either side............................................................................. O. orientalis Doutt

– Propodeum with lateral carinae entire and extending to or almost to anterior margin................................ 8

8 F6 with 2 mps; midlobe of mesoscutum (Fig. 25) with narrow median groove extending from posterior margin anteriorly about 0.25× length........................................................................ O. spartak Triapitsyn

- F6 without mps; midlobe of mesoscutum (Fig. 11) with median groove extending anteriorly almost 0.7× length............................................................................................... O. lapen Triapitsyn

9 Clava with 8 mps.................................................................................... 10

- Clava with 7 mps.................................................................................... 12

10 F4 without mps; ovipositor (Fig. 4) at most occupying about 0.4× length of gaster.................................................................................................... O. innermongolicus Aishan & Hu, sp. nov.

- F4 with 1 or, usually 2 mps; ovipositor occupying at least about 0.9× length of gaster.............................. 11

11 Clava 2.8–3.1× as long as wide (Fig. 13); petiole 0.9–1.1× as long as metacoxa; ovipositor (Fig. 16) extending beyond apex of gaster by 0.12× its own length and 1.4× length of metatibia................................. O. lokomotiv Triapitsyn

– Clava 3.3–3.6× as long as wide; petiole 1.2–1.4× as long as metacoxa; ovipositor extending beyond apex of gaster by less than 0.1× its own length and 1.0–1.2× length of metatibia.......................................... O. insignis Haliday

12 Propodeum with median carina incomplete, almost absent or at least not extending to anterior margin of propodeum.......................................................................................... O. sublaevis Foerster

- Propodeum with median carina extending to anterior margin of propodeum...................................... 13

13 Funicle with F1–F6 lacking mps......................................................... O. vulgatus Haliday

- Funicle with at least 1 mps on F4, F5 or F6................................................................ 14

14 Metacoxa dark brown or black, almost same color as mesosoma; midlobe of mesoscutum without a median groove or at most with a very short median groove..................................................... O. himalayus Subba Rao

- Metacoxa yellowish or brown, different in color from mesosoma; extent of median groove on mid lobe of mesoscutum variable............................................................................................... 15

15 F6 without mps......................................................................... O. notatus Walker

- F6 with 1 or 2 mps................................................................................... 16

16 F4 without mps.......................................................................... O. us Triapitsyn

- F4 with 2 mps....................................................................................... 17

17 Propodeum with median areole separated from metascutellum by longitudinal median carina, and lateral carina with an anterior bifurcation; ovipositor at least 1.1× as long as metatibia......................................... O. novickyi Soyka

- Propodeum with median areole abutting metascutellum, the median carina replaced by two submedian carinae forming inner margin of dorsolateral areoles, and lateral carina without an anterior bifurcation; ovipositor at most 0.9× as long as metatibia.................................................................................. O. huberi Bai, Jin & Li