An Exotic Parasite versus Native Silk Moth Caterpillars

     The ecological effects of nonnative invasive plants, insects, and microbes are gaining wide attention. One group of concern are generalist insect parasites that have been released intentionally as biological control agents, but also attack nontarget native insects. Compsilura concinnata, for example, is a tachinid fly that was released in North America numerous times over an eighty year period to help control the gypsy moth and other pests. Compsilura attacks the larvae of close to two hundred native species of moths and butterflies, beetles, and sawflies.

     In Massachusetts, where the gypsy moth and Compsilura have been well established for decades, field experiments established that the fly is responsible for heavy mortality of cecropia and promethea moth caterpillars (1). Boettner et al. propose that the parasite is partly responsible for regional declines in silk moth populations.

     The gypsy moth is a more recent arrival to Virginia, and in fact it has not yet been recorded on the Sweet Briar campus. UV light censuses conducted by L. Fink and L.P. Brower in Nelson County VA in 1999 and 2000 have established that local saturniid populations are booming. For these reasons, Shelly predicted that Compsilura parasitism would be a less important mortality factor for local silk moths. She tested this hypothesis with luna and cecropia moth caterpillars, set out in Fern Woods and then collected to complete their development in the lab.