Characterization of the Natural Enemy Community, With Emphasis on Entomopathogens, for Management of Western Corn Rootworm (Diabrotica virgifera virgifera)

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the western corn rootworm (WCR), is a major pest of corn ( Zea mays L.) in the United States and Europe. WCR management options comprise mainly transgenic hybrids, insecticide applications and crop rotation. WCR is highly adaptable to management practices and field-evolved resistance to transgenic corn, insecticides and crop rotation in the United States Corn Belt has been reported. Therefore, the motivation for this project was to look into alternative options for WCR management. The goal of this dissertation is to characterize the natural enemies from irrigated commercial cornfields in Nebraska and examine their potential as biological control agents of the WCR. We surveyed five cornfields to document populations of arthropod predators, entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Yellow sticky cards and dry pitfalls captured a diverse community of above-ground natural enemies but their impact on WCR population dynamics is unlikely. In the laboratory, we isolated EPF and EPN species from soil samples using a baiting technique with Galleria mellonella L. and Tenebrio molitor L. Entomogenous fungi with a variety of ecological roles were detected in every cornfield. Entomopathogenic fungi made up the majority of isolates, primarily represented by Metarhizium, but other genera of known and potential EPF include Beauveria, Penicillium, Pseudogymnoascus, and Purpureocillium. In the laboratory, forty-eight strains were screened against WCR larvae. Results showed that Metarhizium anisopliae, M. robertsii, Pseudogymnoascus sp. and BotaniGard (Beauveria bassiana) caused mortality higher than the control and should be explored further in field studies. Six strains that were tested against the WCR can also infect prepupae of western bean cutworm ( Striacosta albicosta Smith), another damaging pest of corn in Nebraska. We also determined that EPN strains of Heterorhabditis bacteriophora Poinar and Steinernema spp. are present in Western Nebraska cornfields. An inoculation project with commercial and New York strains of EPN did not cause significant mortality in WCR populations, potentially due to native Steinernema spp. being present in the control plots. Describing the natural enemy community from WCR-infested fields is a necessary first step in the exploration of biological control as a management tool against this devastating pest