Collyria calcitrator (Grav.) is an important parasite of the wheat stem sawflies Cephus pygmaeus (L.) and C. (Trachelus) tabidus (F .) in Europe (Salt, 193 1). It was imported from England and released against the wheat stem sawfly, Cephus cinctus Nort., in the Prairie Provinces, especially Saskatchewan, from 1930 to 1939. One of its usual hosts, the European wheat stem sawfly, C. pygmaeus, first reported in Ontario in a meadow near Ottawa in 1887 (Harrington, 1890), was first recorded as damaging wheat in Ontario in the counties of Hastings, Prince Edward, and York in 1938. I t was a serious pest in New York and Pennsylvania in the early 1920's (Ries, 1926). As C. cinctus was a major pest of wheat in Western Canada and C. pygmaeus a pest in New York and Pennsylvania, the discovery of moderate to heavy infestations of C. pygmaeus in several localities in south-central Ontario in 1939 by Mr. G. H. Hammond, Entomology Field Station, Marmora, caused concern about the future importance of the sawfly as a pest of wheat in Ontario. C. calcitrator was being imported from England for release against C. cincctus in Western Canada at the time and advantage was taken of the opportunity to release the parasite in Ontario as a possible aid in control.