Reduced Compsilura Concinnata Parasitism Of New England Saturniid Larvae

In the northeastern U.S.A., the non-native generalist parasitoid Compsilura concinnata, introduced in the early 20th Century to control forest pests, has been linked to the decline of giant silk moths (Lepidoptera: Saturniidae). Field research conducted in New England in the late 1990s on two saturniid species, Hyalophora cecropia and Callosamia promethea, found that C. concinnata parasitized 81% and 68%, respectively, when larvae were reared outdoors and replaced weekly. These parasitism rates, extrapolated over the larval period, would prevent any larvae from reaching pupation. In 2017 and 2018, this field experiment was repeated using these same two saturniid species for the same duration and at the same site, location and time of year. In 2017, C. concinnata parasitized only 19% of H. cecropia larvae and 1% of C. promethea larvae; in 2018, parasitism rates were 3% and 0%, respectively.