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ENVIRONMENTAL IMPACTS : PEST DYNAMICS INCLUDING RESISTANCEresistance. The mandated high-dose/refuge strategy for delaying pest resistancerequires planting refuges of toxin-free crops near Bt crops to promote survival ofsusceptible pests. We report that pollen-mediated gene flow up to 31 m from Btmaize caused low to moderate Bt toxin levels in kernels of non-Bt maize refugeplants. Immunoassays of non-Bt maize sampled from the field showed that themean concentration of Bt toxin Cry1Ab in kernels and the percentage of kernelswith Cry1Ab decreased with distance from Bt maize. The highest Bt toxinconcentration in pooled kernels of non-Bt maize plants was 45% of the meanconcentration in kernels from adjacent Bt maize plants. Most previous work ongene flow from transgenic crops has emphasized potential effects of transgenemovement on wild relatives of crops, landraces, and organic plantings, whereasimplications for pest resistance have been largely ignored. Variable Bt toxinproduction in seeds of refuge plants undermines the high-dose/refuge strategyand could accelerate pest resistance to Bt crops. Thus, guidelines should berevised to reduce gene flow between Bt crops and refuge plants.28. Tabashnik BE, Gould F and Carriere Y (2004) : Delaying evolution of insectresistance to transgenic crops by decreasing dominance and heritability.J Evol Biol. 17(4) : 904-12.The refuge strategy is used widely for delaying evolution of insect resistance totransgenic crops that produce Bacillus thuringiensis (Bt) toxins. Farmers growrefuges of host plants that do not produce Bt toxins to promote survival ofsusceptible pests. Many modelling studies predict that refuges will delayresistance longest if alleles conferring resistance are rare, most resistant adultsmate with susceptible adults, and Bt plants have sufficiently high toxinconcentration to kill heterozygous progeny from such matings. In contrast, basedon their model of the cotton pest Heliothis virescens, Vacher et al. (Journal ofEvolutionary Biology, 16, 2003, 378) concluded that low rather than high toxindoses would delay resistance most effectively. We demonstrate here that theirconclusion arises from invalid assumptions about larval concentration-mortalityresponses and dominance of resistance. Incorporation of bioassay data from H.virescens and another key cotton pest (Pectinophora gossypiella) into a populationgenetic model shows that toxin concentrations high enough to kill all or nearly allheterozygotes should delay resistance longer than lower concentrations.29. Zwahlen, C. & Andow, D.A. (2005) : Field evidence for the exposure ofground beetles to Cry1Ab from transgenic corn. Environ. Biosafety Res. 4:113-117.Non-target organisms associated with the soil might be adversely affected byexposure to the CrylAb protein from Bacillus thuringiensis (Bt) in transgenic corn(Zea mays L.) : To check for such exposure, we used ELISA to test for Cry1Ab inground beetles collected live from fields with Bt corn residues and Bt corn (Bt/Bt): Bt corn residues and non-Bt crops (Bt/non-Bt) : or non-Bt corn residues and non-Bt crops (non-Bt/non-Bt) : In fields with Bt corn residues (Bt/Bt and Bt/non-Bt) :Cry1Ab was present in all seven species of ground beetles examined (Agonum(137)