A large genus with a worldwide distribution. Very difficult to identify to species level. Female funicle 3-segmented and male 4-segmented, notauli complete.

Aprostocetus: Submarginal vein in forewing with 2-5 (usually 3 or more) dorsal setae, propodeum with an unbranched medial carina (ridge).
Tetrastichus: Submarginal vein in forewing with one dorsal seta, propodeum with a carina (ridge) branched like an inverted "Y".
Quadrastichus and Oomyzus also share the single seta on the submarginal vein with Tetrastichus, but they lack the Y-shaped propodeal carina. 

Unless identified by a recognized expert, explain how the specimen was identified and include photos of key features. 

All year.

Parasitoids of Diptera, Cynipidae, Coleoptera, or eriophyid mites within galls. 

Unknown.

Unknown.

Graham M.W.R. de V. (1991) A reclassification of the European Tetrastichinae (Hymenoptera: Eulophidae): revision of the remaining genera. Memoirs of the American Entomological Institute, 49: 1-322.