Opius caesus Haliday, 1837: 215.
Opius (Tolbia) caesus: Fischer, 1972: 347.
Synonyms. Opius aquaticus Muesebeck, 1967; Opius hydrelliae Muesebeck, 1933; Opius hydrellianus Fischer, 1971 a; Opius punctiventris Thomson, 1895; Opius subtilis Szépligeti, 1898.
Distribution in Turkey. Edirne, Balikesir, Kirklareli (Fischer & Beyarslan, 2005 a).
Hosts. Diptera. Agromyzidae: Phytomyza primulae Robineau-Desvoidy, 1851. Ephydridae: Hydrellia cochleariae Haliday, 1839; Hydrellia griseola (Fallén, 1813). Drosophilidae: Scaptomyza graminum (Fallén, 1823).
Distribution. Nearctic, Oriental, Palaearctic. Austria, Bulgaria, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Iceland, Ireland, Italy, Lithuania, Nepal, Poland, Romania, Russia, Spain, Sweden, Switzerland, Syria, Tajikistan, Turkey, U.S.A., United Kingdom, Yugoslavia, Serbia.