9615299 LOUDA The investigators propose to measure the impact of the flowerhead weevil (Rhinocyllus conicus), released for biological control of exotic thistles, on native plants and the insects associated with them. Experiments will measure the effects of the timing of flowering by native thistles on the impact of weevils, the effect of the weevil on seed production of native thistles, and whether superior competitive ability of the introduced weevil is responsible for the population decline of native insects. The expected outcomes include: documentation of the extent and impact of the feeding by the exotic weevil on two native plants in the upper Great Plains, assessment of the role of plant growth patterns on weevil use and impact, and determination of the direct ecological consequences of shifting host use by a deliberately introduced insect. The study will be the first to experimentally assess the ecological consequences of unintended feeding on native host plants by an insect deliberately introduced into the USA to control exotic weeds. Biological control of weeds is increasingly advocated as an environmental alternative to herbicides. Yet, few data are available with which to evaluate environmental risks of introducing exotic insects in biological control programs. The study will provide important data on such consequences when transference occurs and, thus, on potential ecological risks associated with classical biological control of weeds. Such information should prove useful in future attempts to control invasive exotic weeds.
