Effects of a biological control introduction on three nontarget native species of saturniid moths

Damage to nontarget (native) invertebrates from biological control introductions is rarely documented. We examined the nontarget effects of a generalist parasitoid fly, Compsilura concinnata (Diptera: Tachinidae), that has been introduced repeatedly to North America from 1906 to 1986 as a biological control agent against 13 pest species. We tested the effect of previously established populations of this fly on two native, nontarget species of moths (Lepidoptera: Saturniidae), Hyalophora cecropia and Callosamia promethea, in Massachusetts forests. We estimated survivorship curves for newly hatched H. cecropia larvae (n = 500), placed five per tree in the field and found no survival beyond the fifth instar. We simultaneously deployed cohorts (n = 100) of each of the first three instars to measure the effect of parasitoids during each stage of development. C. concinnata was responsible for 81% of H. cecropia mortality in the first three instars. We deployed semigregarious C. promethea in aggregations of 1-100 larvae in the field and recorded high rates of parasitism by C. concinnata among C. prometheca larvae exposed for 6 days (69.8%) and 8 days (65.6%). We discovered a wild population of a third species of silk moth, the state-listed (threatened) saturniid hemileuca maia maia, and found that C. concinnata was responsible for 36% (n = 50) mortality in the third instar. Our results suggest that reported declines of silk moth populations in New England may be caused by the importation and introduction of C. concinnata.