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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGICALLY BASED PEST MANAGEMENT IN MODERN CROPPING SYSTEMS

Location: North Central Agricultural Research Laboratory

Title: Effects of entomopathogens on mortality of western corn rootworm and fitness costs of resistance to Cry3Bb1 maize

Authors
item Hoffmann, Amanda -
item French, Bryan
item Jaronski, Stefan
item Gassmann, Aaron -

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2013
Publication Date: N/A

Interpretive Summary: Fitness costs can delay pest resistance to crops that produce insecticidal toxins. Previous research has found that entomological pathogens impose fitness costs on Bt resistance. Additionally, entomological pathogens can be used for integrated pest management by providing biological control of pests. The western corn rootworm (WCR) is a major pest of corn and is currently managed using Bt corn. We tested whether entomological pathogenic nematodes and fungi increased mortality of western corn rootworm and whether these entomological pathogens increased fitness costs of resistance to corn producing the Cry3Bb1 toxin. We exposed WCR larvae to two species of nematodes, Heterorhabditis bacteriophora and Steinernema feltiae, and to two species of fungi, Beauveria bassiana and Metarhizium brunneum in two assay types: seedling mat and small cup. Larval mortality increased with the concentration of H. bacteriophora and S. feltiae nematodes in the small cup assay, and mortality from was significantly greater than zero for all entomological pathogens in both assays, with the exception of S. feltiae and B. bassiana in the seedling mat assay. However, no fitness costs were observed in either assay type for any pathogen. The increased mortality of WCR larvae caused by these pathogens supports their potential use in biological control; however, the lack of fitness costs suggests that entomological pathogens will not delay the evolution of Bt resistance in WCR.

Technical Abstract: Fitness costs can delay pest resistance to crops that produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) and past research has found that entomopathogens impose fitness costs of Bt resistance. Additionally, entomopathogens can be used for integrated pest management by providing biological control of pests. The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of maize and is currently managed by planting of Bt maize. We tested whether entomopathogenic nematodes and fungi increased mortality of western corn rootworm and whether these entomopathogens increased fitness costs of resistance to Cry3Bb1 maize. We exposed western corn rootworm larvae to two species of nematodes, Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), and to two species of fungi, Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) (strain GHA) and Metarhizium brunneum (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae) (strain F52) in two assay types: seedling mat and small cup. Larval mortality increased with the concentration of H. bacteriophora and S. feltiae in the small cup assay, and mortality from entomopathogens was significantly greater than zero for all entomopathogens in both assays, with the exception of S. feltiae and B. bassiana in the seedling mat assay. However, no fitness costs were observed in either assay type for any entomopathogen. The increased mortality of western corn rootworm larvae caused by these entomopathogens supports their potential use in biological control; however, the lack of fitness costs suggests that entomopathogens will not delay the evolution of Bt resistance in western corn rootworm.

Last Modified: 8/22/2014
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