Competition between Lysiphlebus testaceipes and Coccinellidae in winter wheat agroecosystems

The endoparasitic wasp, Lysiphlebus testaceipes Cresson, along with the ladybeetle predators Hippodamia convergens Guerin-Meneville and Coccinella septempunctata L. constitute part of an aphidophagous guild responsible for supressing greenbug, Schizaphis graminum Rondani, populations below economic injury levels in the Southern Great Plains. These ladybeetles will consume L. testaceipes within their aphid hosts, a dynamic known as intraguild predation. The studies described in this dissertation were conducted to examine the effects of aphid parasitism by L. testaceipes on life history outcomes of H. convergens and C. septempunctata and subsequent competitive dynamics between them. Gravid female C. septempunctata and H. convergens exhibited no significant preference between winter wheat plants infested with either unparasitized or parasitized greenbugs in a y-tube olfactometer choice test. Gravid females under no-choice conditions showed no ovipositional restraint in the presence of parasitized prey. Early instar coccinellid larvae were unable to consume mummified aphid prey resulting in complete mortality. Parasitism of greenbugs by L. testaceipes significantly reduced overall survival of H. convergens and C. septempunctata in microcosm and arena experiments, enhancing the strength of cannibalism and intraguild predation interactions with C. septempunctata being the dominant intraguild predator, however C. septempunctata due to its larger size and nutritional requirements suffered greater adverse effects from parasitism. Therefore, where L. testaceipes is present at high enough levels in field settings it likely alters the outcome of competition between native and exotic ladybeetle species and potentially turns that habitat/patch into a sink for coccinellid populations.