Monday, December 11, 2006 - 10:23 AM

Potential impacts of refuge contamination on Bt resistance in pink bollworm

Shannon M. Heuberger,, Yves Carrière,, Timothy J. Dennehy,, and Bruce E. Tabashnik, University of Arizona, Dept. of Entomology, P.O. Box 2100 (36), Tucson, AZ

Refuges of non-Bt cotton are used to delay resistance to Bt cotton in pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae), a pest that eats cotton seeds. However, contamination of refuges by Bt transgenes could reduce the efficacy of this strategy. In previous study, we identified two forms of Bt contamination in refuges: 1) adventitious Bt cotton plants, with 70-100% of their seeds producing Bt toxin, and 2) non-Bt cotton plants that outcrossed with Bt plants, resulting in bolls that typically contained 5-20% seeds with Bt toxin. Here we used laboratory bioassays to evaluate the potential impacts of contaminant bolls on feeding behavior and survival of pink bollworm that were resistant (rr), susceptible (ss), or heterozygous for resistance (rs) to Bt toxin. In feeding preference tests, rs larvae showed a mild preference for non-Bt seeds over Bt seeds, but rr and ss larvae did not discriminate between Bt and non-Bt seeds. On simulated outcrossed cotton bolls (a mixture of cotton seeds with 20% Bt and 80% non-Bt), survival of rr and rs did not differ from ss. On simulated adventitious bolls (70 or 100% Bt cotton seeds), rr individuals had higher survival compared to ss, although survival between rs and ss individuals did not differ. Results from a simple analytical model suggest that adventitious Bt plants impact resistance evolution to a greater extent than Bt-outcrossed plants, especially when refuge sizes are small.

Species 1: Lepidoptera Gelechiidae Pectinophora gossypiella (pink bollworm)