Postdoctoral Associate Cornell University Ithaca, New York
Beneficial carabid beetles inhabiting agroecosystems are at risk of insecticides used to control crop pests. In watermelon production, the most serious pest is the striped cucumber beetle, Acalymma vittatum, which most farmers manage with neonicotinoids applied as a soil drench and regular “calendar” sprays of pyrethroids as conventional pest management. An alternative strategy is integrated pest management where pest abundance is monitored and pyrethroids are applied only if pests exceed the economic threshold of 5 beetles per plant. Carabids exposed to insecticides by contact or through their diets (leaves, seeds, and prey) can have lethal and sublethal effects due to toxic and/or low food availability. We evaluated the effect of these pest management practices on the morphometric traits of two numerically dominant carabid predators, Harpalus pensylvanicus and Poecilus chalcites. Both species were collected from watermelon under conventional and integrated management (5 fields each) during the summer growing season over two years. The length of the elytra, hind femur and pronotum were measured in 663 H. pensylvanicus and 566 P. chalcites. A MANOVA and Games Howell were used to test the effect of pest management on these morphometric traits. H. pensylvanicus females and males from conventional management had shorter pronotums and hind femurs, while P. chalcites females had larger pronotums and hind femurs but P. chalcites males only had larger hind femurs. Pest management effects on carabid body size can have negative and positive effects on fitness and the ecosystem service (predation) they provide.
