Key to species of the genus Trachyusa Ruthe

1 Body slender in lateral view (Figs 9, 11, 13, 15); mesoscutum in dorsal view longer than its maximum width (Figs 10D, 12D, 14D, 16C); antenna longer than body length................................................................ 2

- Body stout in lateral view; mesoscutum in dorsal view shorter than wide; antenna as long as or shorter than body length... 7

2 Mesoscutum with conspicuous long setae and anteriorly near notauli with some distinct punctures (Fig. 10D); head less transverse in dorsal view, 1.5–1.7 × wider than long medially (Fig. 10I); pterostigma of ♀ less robust, vein r 0.4–0.5 × as long as maximum width of pterostigma (Fig. 10A); China (Shaanxi, Zhejiang)........................ T. punctata sp. nov .

- Mesoscutum only with medium-sized setae medio-anteriorly and anteriorly near notauli smooth; head usually distinctly transverse (except in T. aurora), 1.7–2.2 × wider than long medially (Figs 12I, 14I, 16H); if 1.5–1.7 × then pterostigma of ♀ robust, vein r 0.2–0.3 × as long as its maximum width........................................................ 3

3 Head less transverse in dorsal view, 1.5–1.7 × wider than long medially; with some indistinct granulation near notauli; vein m-cu of fore wing interstitial or nearly so; [NW European T. nigrothoracica van Achterberg & O’Connor, 1990, is provisionally considered to be a melanistic form of T. aurora]; Europe, East Palaearctic (Far East Russia, Korea)................................................................................................... T. aurora (Haliday, 1838)

- Head more transverse, 1.7–2.2 × wider than long medially (Figs 12I, 14I, 16H); area near notauli smooth; vein m- cu of fore wing antefurcal or postfurcal (Figs 12A, 14A, 16H).......................................................... 4

4 Notauli smooth and almost reaching middle of mesoscutum (Fig. 12D), medio-posterior depression short and shallow (Fig. 12D); [precoxal sulcus short, reduced near posterior edge of mesopleuron (Fig. 12C)]; China (Guizhou)................................................................................................. T. microporosa sp. nov.

- Notauli distinctly sculptured, at least so anteriorly (Fig. 14D); if sculpture of notauli reduced then medio-posterior depression long and posteriorly rather deep......................................................................... 5

5 Medio-posterior depression of mesoscutum short; precoxal sulcus long, wide and distinctly developed near posterior edge of mesopleuron; vein m-cu of fore wing slightly postfurcal; East Palaearctic (Far East Russia)... T. indrik Belokobylskij, 1998

- Medio-posterior depression of mesoscutum long (Fig. 14D); precoxal sulcus short, absent near posterior edge of mesopleuron (Fig. 14C); vein m-cu of fore wing slightly antefurcal (Fig. 14A)............................................... 6

6 Mesosoma and metasoma black or dark reddish brown (Figs 14D–F); pterostigma of ♂ (compared to ♀) strongly widened; first flagellomere 3.5–4.3 × longer than its apical width (Fig. 14H); hind coxa more or less sculptured (Figs 14C); notauli narrowly sculptured (Figs 14D); [head 1.7–1.9 × wider than long medially]; Russia ( Far East), China (Guizhou, Shaanxi)..................................................................................... T. vasilisk Belokobylskij, 1998

- Mesosoma and metasoma brownish yellow (Figs 16C–E), but apex of metasoma and propodeum (especially of ♂) more or less darkened; pterostigma of ♂ (compared to ♀) moderately widened; first flagellomere 4.5–5.8 × longer than its apical width (Fig. 16G); hind coxa smooth (Fig. 15); notauli often more extensively sculptured (Fig. 16C); [head 1.7–2.3 × wider than long medially]; China (Guizhou, Hebei, Liaoning, Shaanxi, Zhejiang)............................. T. whartoni Yao, 2015

7 Notauli on posterior half of mesoscutal disc deeply impressed; mesoscutum black; first metasomal tergite usually slenderer (Fig. 15 in van Achterberg & O’Connor 1990); Central Europe.............................. T. szepligetii Papp, 1967

- Notauli on posterior half of mesoscutal disc at most shallowly impressed; mesoscutum brownish yellow; first tergite rather robust (Fig. 14 in van Achterberg & O’Connor 1990); Central Europe....................... T. bucephala Papp, 1967