Key to West Palaearctic species of the genus Diostracus (males)

Note: Partially based on previous keys to species of the former genus Sphyrotarsus (Parent 1938; Negrobov 1978).

1. Scutellum with 1–2 pairs of long bristles and with some short lateral setae or hairs............2

– Scutellum with 3 pairs of almost equally long bristles (subgenus Sphyrotarsus).....................4

2. Scape with hairs above; 4.5–5.1 mm ............................. D. (Diostracus) leucostomus (Loew, 1861)

– Scape bare above..............................................................................................................................3

3. Male and female postpedicel elongate-ovate, 1.5–2 times longer than high, with apical stylus; male abdominal sternites without strong spines; body 5 mm long ................................................ ..................................................................................... D. (Takagia) stackelbergi (Negrobov, 1965)

– Postpedicel about as long as high, with dorsal stylus; male 2 nd to 4 th abdominal sternites with strong black spines; body 5–6.5 mm long .............. D. (Lagodechia) spinulifer Negrobov & Zurikov, 1988

4. Male 2 nd and 3 rd abdominal sternites with strong black spines; body 7.0 mm (female) to 9.4 mm (male) long ....................................................................................... D. (S.) kustovi sp. nov.

– Male abdominal sternites without strong spines............................................................................5

5. Male cercus shorter than epandrium; body 6 mm long ....... D. (S.) caucasicus (Negrobov, 1965)

– Male cercus longer than epandrium................................................................................................6

6. All tarsi with empodium scaly in male, as long as claws; mid basitarsus thin, longer than rest of tarsomeres combined; body 6.5 mm long ............................ D. (S.) hygrophilus (Becker, 1891)

– Tarsi with reduced empodium; mid basitarsus shorter than rest of tarsomeres combined.......7

7. Male cercus bifurcated between base and middle; mid basitarsus thickened at middle and at apex................................................................................................................................................8

– Male cercus bifurcated at apex only; mid basitarsus simple or thickened at base..................9

8. Outer arm of cercus long and narrow; body 5.2–6 mm long ..... D. (S.) argyrostomus (Mik, 1874)

– Outer arm of cercus short, broad, subtriangular; body 7 mm long ...... D. (S.) parenti (Hesse, 1933)

9. Palpus bare; proboscis as long as head; body 5.2 long ..................... D. (S.) hessei (Parent, 1914)

– Palpus covered with black hairs; proboscis half as long as head; body 6–6.5 mm long ............. .................................................................................................... D. (S.) hervebazini (Parent, 1914)