Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2010
Publication Date: 10/1/2010
Publication URL: www.bioone.org/doi/pdf/10.1603/EC10087
Citation: Hannon, E., Sisterson, M.S., Stock, P., Carriere, Y., Tabashnik, B., Gassmann, A. 2010. Effects of four entomopathogenic nematode species on fitness costs of pink bollworm resistance to Bacillus thuringiensis toxin Cry1Ac. Journal of Economic Entomology. 103:1821-1831. Interpretive Summary: Genetically modified crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) are planted world-wide. Large-scale planting of Bt crops places strong pressure on target pests to evolve resistance to Bt toxins. Application of an agent that causes higher mortality in insects resistant to Bt toxin compared to insects susceptible to Bt toxin could slow resistance evolution. The mortality of pink bollworm (Pectinophora gossypiella) susceptible and resistant to Bt toxin Cry1Ac was evaluated in the presence of four nematode species, Steinernema riobrave, S. carpocapsae, S. sp. (ML18), and Heterorhabditis sonorensis. Mortality of pink bollworm susceptible and resistant to Bt toxin Cry1Ac differed only in the presence of S. riobrave. Incorporation of nematode-imposed fitness costs into a spatially-explicit simulation model suggests that in a landscape consisting of a mixture of Bt crop fields and non-Bt crop fields application of S. riobrave to non-Bt crop fields could substantially delay the evolution of resistance to Bt toxin by the pink bollworm. Results from this study provide researchers with important information on fitness costs associated with resistance to Bt toxin and its potential application to improving resistance management.
Technical Abstract: Evolution of resistance by pests can reduce the efficacy of transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt). However, fitness costs can slow the evolution of resistance. We tested whether four species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) could magnify fitness costs of resistance to Bt toxin Cry1Ac in pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae). In laboratory experiments, the magnitude and dominance of fitness costs were significantly increased by the nematode Steinernema riobrave, but not by Steinernema carpocapsae, Steinernema sp. (ML18), or Heterorhabditis sonorensis. Results of computer simulations incorporating nematode-imposed fitness costs suggest that in a landscape where non-Bt crop refuges account for 20% of all fields, treating 8% of refuge fields with S. riobrave could substantially increase the delay in pink bollworm resistance to Bt cotton. We conclude that entomopathogenic nematodes could bolster management of insect resistance to Bt crops, but the success of this approach is likely to depend on careful selection of an appropriate nematode species.