The establishment of exotic coccinellid species may be related to the decline in native coccinellid species within the United States. Coccinellids may interact indirectly by competing for shared resources and directly through intraguild predation. Prior studies have examined pairwise interactions among species and although several coccinellid species typically co-exist within habitats, multi-species interactions have rarely been investigated. To examine how aphid prey levels influence interspecific interactions among a multispecies assemblage, the exotic coccinellids, Harmonia axyridis (Pallas) and Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and a native coccinellid species, Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), were paired or placed in groups containing three heterospecific larvae and fed 2.4, 12.0, or 24.0 mg of aphids per larva daily. Larval survival, developmental time, and adult weight of individuals were measured. Greater amounts of prey typically resulted in increased adult weights and shorter developmental times. When Coleomegilla maculata and Coccinella septempunctata were paired, Coleomegilla maculata had higher survival rates at low prey levels and Coccinella septempunctata had higher survival at mid- and high prey levels. When the three species were combined, Coccinella septempunctata and Coleomegilla maculata had similar survival rates (17%) at low prey levels; at mid- and high prey levels, Coccinella septempunctata survival increased (58–88%), but Coleomegilla maculata survival remained similar (17–21%). Survival of H. axyridis was not affected by competitors. Even though intraguild predation occurs among these species, the responses to competitors varied based on prey level, coccinellid species, and the number of interacting larvae.
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Vol. 102 • No. 3