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Sources, sinks, and zone of influence of refuges for managing insect resistance to Bt crops.
Carriere, Yves*,1, Dutilleul, Pierre2, Ellers-Kirk, Christa1, Pedersen, Brent3, Haller, Shirley4, Antilla, Larry4, Dennehy, Tim1, Tabashnik, Bruce1, 1 Department of Entomology, Tucson, AZ2 Department of Plant Science, Ste-Anne-de-Bellevue, Quebec, Canada3 University of California, Berkeley, CA4 Arizona Cotton Research and Protection Council, Phoenix, AZ
ABSTRACT- The refuge / high-dose strategy is central for delaying insect resistance to transgenic crops that produce Bacillus thuringiensis (Bt) toxins, but determining the optimal spatial configuration of refuges has been problematic. We used Geographic Information System (GIS) mapping of cotton fields and pheromone trapping of moths throughout Arizona to estimate the appropriate distance between Bt cotton and external refuges of non-Bt cotton for the pink bollworm, a major cotton pest. Our results show that non-Bt cotton fields were sources and Bt cotton fields were sinks for pink bollworm populations. In both years studied, refuges at 0.75 km or less from Bt cotton had the greatest potential for delaying resistance. However, the average distance at which refuges would not contribute migrants to a Bt cotton field increased from 0.75 km in the first year to 2.25 km in the second year. An increase in the relative abundance of non-Bt cotton in the second year may have altered source-sink dynamics and contributed to this change. The spatially explicit approach described here delimits the zone of influence of refuges in the field, a key step in determining the spatial configuration of refuges for delaying pest resistance to Bt crops.
KEY WORDS: transgenic crops, metapopulations, dispersal, GIS