The species discussed below was first recorded under the name Synetaeris n. sp. as a parasite of the spruce budworm, Choristoneura fumiferana Clem., in Ontario by McGugan and Blais (1959), although they point out that it may have been collected from budworm in British Columbia during the 1940's but incorrectly identified at that time. These authors collected S. tenuifemur during the declining years of a budworm outbreak in the Lake Nipigon region of northwestern Ontario, and it was during the declining years of a severe outbreak that the parasite was first reared from budworm in the Green River area of north-western New Brunswick (Morris, 1963, in press). These data suggest that S. tenuifemur is associated with endemic budworm populations, an assumption advanced by McGugan and Blais (1959). However, it was not found in the Green River area from 1945 to 1947 when budworm density was at a low level prior to the 1949-1959 outbreak.