Benefits and harm caused by the introduced generalist tachinid, Compsilura concinnata, in North America

We review North American research on Compsilura concinnata (Meigen), a highly generalist tachinid parasitoid that was introduced in 1906 to control two invasive forest insects: gypsy moth and browntail moth. The impact on gypsy moth in natural populations in North America has long thought to be minor, a view confirmed by recent work in Canada and Wisconsin, USA. However, research with experimentally created populations of gypsy moth suggests that it may be more important than previously realized. Studies on browntail moth in both naturally occurring and experimental populations suggest that C. concinnata is probably the main reason browntail moth disappeared from most of its former range in North America. Research on giant silk moths suggests that C. concinnata has become the major source of mortality among several species and may be responsible for the notable decline in their densities that has occurred over the last century. C. concinnata has been touted as a premier example of the generalist natural enemy that should be avoided in classical biological control introductions, yet in the case of browntail moth its effect has been extremely beneficial.