ECOLOGICAL EFFECTS OF AN INSECT INTRODUCED FOR THE BIOLOGICAL-CONTROLOF WEEDS

Few data exist on the environmental risks of biological control. The w eevil Rhinocyllus conicus Froeh., introduced to control exotic thistle s, has exhibited an increase in host range as well as continuing geogr aphic expansion. Between 1992 and 1996, the frequency of weevil damage to native thistles consistently increased, reaching 16 to 77 percent of flowerheads per plant. Weevils significantly reduced the seed produ ction of native thistle Rowerheads. The density of native tephritid fl ies was significantly lower at high weevil density. Such ecological ef fects need to be better addressed in future evaluation and regulation of potential biological control agents.