Parasitoid-mediated apparent competition between native and exotic lady beetle populations in Ohio

Following the introduction of exotic coccinellid species, a decline in several native lady beetle species has been observed in the United States. Although the cause of native decline is not known, the majority of hypotheses are linked in part to the introduction of exotic competitors. We investigated apparent competition as a mechanism to explain native coccinellid decline. This describes competition between two organisms mediated by a predator, parasitoid, or disease. Following the apparent competition hypothesis, the introduction of exotic lady beetles has a negative impact on native species by allowing populations of shared parasitoids to increase. This leads to higher rates of parasitism among native species. The goal of this project was to determine if the diversity and abundance of exotic coccinellids present in a given landscape influences parasitism of native coccinellids via parasitoid-mediated apparent competition. Across Ohio, eight landscapes were selected that ranged in composition and heterogeneity. Within each landscape, adult coccinellids were collected from three different habitats: soybean, alfalfa, and grassland. Ten 20-sweep samples were collected twice during the growing season from each site. Coccinellids were placed in individual containers and observed for parasitoid emergence for 24 days, after which all live beetles were frozen and dissected to determine if parasitoid eggs or larvae were present. Once all data are collected (Fall, 2010) we will determine if rates of parasitism among native coccinellid species are influenced by exotic coccinellid diversity and abundance, habitat, or landscape composition and heterogeneity.