Using an F₂ Screen to Search for Resistance Alleles to Bacillus thuringiensis Toxin in European Corn Borer (Lepidoptera: Crambidae)

We present an application of an F₂ screening method for recovering and estimating the frequencies of rare alleles that confer insect resistance to a transgenic corn variety producing Bacillus thuringiensis Berliner crystal protein toxin (Bt corn). Based on a sample of 91 female Ostrinia nubilalis (Hübner) we show with 95% confidence that the frequency of B. thuringiensis resistance alleles from a wild Minnesota population is <0.013. This is an upper limit to the estimated allele frequency and does not provide clear evidence that 1 of the assumptions of the refuge plus high-dose strategy will or will not be met. With additional sampling, a more precise estimate of resistance allele frequency could be obtained that would clearly support or refute 1 of the assumptions of the refuge plus high-dose strategy. Variable costs of the screening method were $19.70 per female line, but these could be reduced by improved collecting, rearing, and handling methods.