Key to European species of the genus Thinoseius (females)

1. Sternal setae st1 and associated pores inserted on small sternal plate connected with endopodals I; dorsal shield with 14 pairs of short, stout setae including j1; length of dorsal shield 400 µm [British Isles].............................................. ............................................................................................................................... Thinoseius acuminatus Evans 1962

- Sternal setae st1 and associated pores inserted on unsclerotised soft integument; dorsal shield never with both 14 pairs of setae and j1 on the shield (11–15 pairs of setae on dorsal shield)................................................................... 2

2. Dorsal setae J 2 in normal position posterolateral to J1; dorsal shield with 15 pairs of setae; length of dorsal shield 750–830 µm [Iceland, Scandinavia, British Isles, Germany, Ukraine, Bulgaria, Latvia, Russia, North America]........ ............................................................................................................................ Thinoseius spinosus (Willmann 1939)

- Dorsal setae J2 with unusual position lateral to J1; dorsal shield with 11–14 pairs of setae........................................ 3

3. Dorsal shield with 14 pairs of setae, including setae Z1 and Z4; epistome with five points [Croatia, Bulgaria]........... ................................................................................................................................. Thinoseius kargi Hirschmann 1966

- Dorsal shield with 11–13 pairs of setae, setae Z1 and Z4 outside the shield; epistome with more than five points; length of dorsal shield 760–850 µm [Iceland, British Isles, Germany, Ukraine, Bulgaria]............................................ ................................................................................................................................. Thinoseius fucicola (Halbert 1920)