Intraguild predation among Coccinellidae and Lysiphlebus testaceipes in an Oklahoma winter wheat system.

摘要

Scope and Method of Study. In 2007, over 6 million acres of wheat were planted in Oklahoma. Whether these 6 million acres are for forage or grain production they are attacked by a number of insect pests; especially the greenbug Schizaphis graminum Rondani which is often the limiting factor in profitable winter wheat production. The endoparasitic wasp, Lysiphlebus testaceipes Cresson, along with the ladybeetle predator Hippodamia convergens Guérin-Méneville constitute part of an aphidophagous guild responsible for maintaining greenbug, Schizaphis graminum Rondani, populations below economic injury levels. These ladybeetles will consume L. testaceipes within their aphid hosts, a dynamic known as intraguild predation. The studies described in this thesis were conducted to examine the occurrence and frequency of this kind of intraguild predation in winter wheat fields and to investigate if and at what stage parasitized aphids are a suitable food source for the development and survival of H. convergens.;Findings and Conclusions. Lysiphlebus testaceipes mitochondrial DNA within the gut of the ladybeetle Hippodamia convergens was detectable with PCR following intraguild predation of the immature parasitoid within its greenbug host. Detection was possible up to 16h post-feeding 100% of the time using Ltesta F & R primers. Three fields of winter wheat were sampled on 24 February, 10 March, and 24 March (2006) for intraguild predation of L. testaceipes by coccinellids; proportion of intraguild predation events of this nature ranged from 0.667 to 0.871. Both 3rd and 4th instar H. convergens larvae were fed 4mg/day of greenbugs in 3 different stages of parasitism by L. testaceipes to determine the suitability of that stage as a food source. Results showed reduced survivability for both 3rd and 4th instar H. convergens larvae when feeding on greenbugs in all stages of parasitism by L. testaceipes with chronic effects having greater negative impacts.