PARASITISM OF NEODIPRION SERTIFER (HYMENOPTERA: DIPRIONIDAE) BY EXENTERUS SPP. (HYMENOPTERA: ICHNEUMONIDAE) IN ONTARIO, 1962–1972, WITH NOTES ON THE PARASITES

Abstract

Four species of Exenterus were reared from the European pine sawfly, Neodiprion sertifer (Geoff.), in Ontario. An introduced species, E. abruptorius (Thunb.), last reported in Ontario in 1948, was recovered in very small numbers at one location. The native E. affinis Roh. (= E. walleyi Cush.) parasitized a small proportion of N. sertifer but was the main species attacking feeding larvae. The native E. nigrifrons (formerly called E. canadensis Prov.) and the introduced E. amictorius (Panz.) occurred at all sampled locations. Both species were more numerous in high than in low density populations of N. sertifer, but E. nigrifrons was more destructive, and E. amictorius less destructive, at high than at low density.About 60% of adults of E. amictorius and 6% of those of E. nigrifrons eclosed in the same summer that attack occurred. Most were unlikely to have reproduced, owing to the scarcity of hosts. In both species females were more frequent in female than in male hosts.Samples of N. sertifer cocoons in July were superior to larval samples in June and cocoon samples in August and the following May for measuring the rate of parasitism and the relative abundance of Exenterus spp. However, because of mortality of Exenterus before and after sampling, data based on the rearing of cocoons seriously underestimated the impact of the parasites.