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Risk Assessment for Helicoverpa zea (Lepidoptera: Noctuidae) Resistance on Dual-Gene Versus Single-Gene Corn

Edwards, Kristine T., Caprio, Michael A., Allen, K. Clint, Musser, Fred R.
Journal of Economic Entomology 2013 v.106 no.1 pp. 382
Bacillus thuringiensis, Helicoverpa zea, bacterial toxins, biological resistance, corn, cotton, crystal proteins, evolutionary adaptation, expert opinion, natural selection, plant-insect relations, population genetics, probability analysis, resistance management, risk, risk assessment, simulation models, transgenic plants, volunteer plants
Recent Environmental Protection Agency (EPA) decisions regarding resistance management in Bt-cropping systems have prompted concern in some experts that dual-gene Bt-corn (Cry1A.105 and Cry2Ab2 toxins) may result in more rapid selection for resistance in Helicoverpa zea (Boddie) than single-gene Bacillus thuringiensis (Bt)-corn (Cry1Ab toxin). The concern is that Bt-toxin longevity could be signiÞcantly reduced with recent adoption of a natural refuge for dual-gene Bt-cotton (Cry1Ac and Cry2Ab2 toxins) and concurrent reduction in dual-gene corn refuge from 50 to 20%. A population genetics framework that simulates complex landscapes was applied to risk assessment. Expert opinions on effectiveness of several transgenic corn and cotton varieties were captured and used to assign probabilities to different scenarios in the assessment. At least 350 replicate simulations with randomly drawn parameters were completed for each of four risk assessments. Resistance evolved within 30 yr in 22.5% of simulations with single-gene corn and cotton with no volunteer corn. When volunteer corn was added to this assessment, risk of resistance evolving within 30 yr declined to 13.8%. When dual-gene Bt-cotton planted with a natural refuge and single-gene corn planted with a 50% structured refuge was simulated, simultaneous resistance to both toxins never occurred within 30 yr, but in 38.5% of simulations, resistance evolved to toxin present in single-gene Bt-corn (Cry1Ab). When both corn and cotton were simulated as dual-gene products, cotton with a natural refuge and corn with a 20% refuge, 3% of simulations evolved resistance to both toxins simultaneously within 30 yr, while 10.4% of simulations evolved resistance to Cry1Ab/c toxin.