Data generation and utilization for evaluating Helicoverpa zea (Lepidoptera: Noctuidae) resistance management in Bt field corn and cotton through computer modeling

Herein, we determine the effects transgenic field corn and cotton expressing Bacillus thuringiensis (Bt) proteins Cry1Ab/Ac & Cry2Ab, both singly and pyramided, on the development and survival of Helicoverpa zea in eastern North Carolina. Bt field corn genotypes significantly reduced larval populations and production of pupae and adults below that of the non-Bt genotype. Larval growth rate, pupal weight, pupal length and eclosion date were also negatively affected by Bt corn genotypes. Bt cotton genotypes significantly reduced the percentage of terminal regions and bolls containing live heliothine larvae and feeding damage compared to the non-Bt genotype. Bt cotton genotypes also significantly lowered bollworm pupal and adult production compared to the non-Bt genotype. Adults from the non-Bt genotype eclosed significantly earlier than adults from all three Bt genotypes.; We also use a simulation computer model to evaluate the role of pyramided Bt cotton and corn cultivars, EPA mandated non-Bt refuges, and soybean as a host in H. zea resistance development to Bt. With at least one pyramided Bt genotype, the model predicts that the 20% sprayed non-Bt cotton refuge's contribution to delaying resistance evolution is greatly supplemented by other non-Bt sources of susceptible moths and has less of an effect on Bt resistance management than the non-Bt corn refuge in eastern North Carolina.; A field study was also conducted to determine what effect seed mixtures of Bollgard II cotton and non-Bt cotton have on fruit damage by H. zea and cotton yield. A lab study determined the efficacy of Bollgard II bolls against feral H. zea larvae (≥3rd instar) that had initially fed on non-Bt cotton. Averaged over years, there were no significant yield differences between any seed mixture despite the 8% non-Bt mixture having significantly higher boll damage than all other treatments; however, when analyzed by year, the 100% Bollgard II treatment in 2005 had significantly higher seed cotton yield than all seed mixture treatments. H. zea larvae (≥3rd instar) survived to adulthood on Bollgard II cotton bolls after initially feeding on non-Bt cotton but at significantly lower percentages than larvae that remained on non-Bt cotton.