Effects of Bt corn and entomopathogens on survival of western corn rootworm

The western corn rootworm Diabrotica virgifera virgifera LeConte is one of the most significant pests of corn in North America. The soil-borne larvae of this pest feed on corn roots, causing yield losses estimated at over one billion dollars annually. Currently, genetically modified corn expressing insecticidal toxins from the bacterium Bacillus thuringiensis is used to manage corn rootworm, although some feeding injury still occurs. Several species of entomopathogenic fungi and nematodes have been shown to be natural enemies of corn rootworm. In this study, we used entomopathogenic nematodes (Steinernema glaseri, S. carpocapsae, and Heterorhabditis bacteriophora) and fungi (Metarhizium anisopliae and Beauveria bassiana) to determine if a blend of entomopathogens could act in a complimentary manner with Bt corn by further reducing rootworm feeding injury and survival. The experiment consisted of a fully crossed design with two corn treatments (Bt corn and non-Bt corn) and two entomopathogen treatments (present or absent). Entomopathogens used in conjunction with Bt corn resulted in the highest mortality for larvae assessed just before pupation. Similarly, the number of adults that emerged from soil was lowest when insects were fed on Bt corn and exposed to pathogens, indicating that entomopathogens enhanced the pest-management benefits conferred by Bt corn.