Verifying an F₁ screen for identification and quantification of rare Bacillus thuringiensis resistance alleles in field populations of the sugarcane borer, Diatraea saccharalis

Using an F₁ screen, 352 feral individuals of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), were examined for the presence of Bacillus thuringiensis (Bt)-resistance alleles. These insects represented four geographical populations collected in central and northeastern Louisiana, USA, and one field population from the Gulf Coast area of Texas, USA, during 2006. The F₁ screen used various crosses between field-collected insects and a laboratory strain of Cry1Ab-resistant D. saccharalis, including both reciprocal crosses and group mating. F₁ neonates of the crosses were screened for Bt resistance on Bt maize leaf tissue. One field-collected individual of D. saccharalis was shown to have a Bt-resistance allele. Based on Bayesian analysis procedures, the Bt-resistance allele frequency in the five populations of D. saccharalis was 0.0028 with a 95% confidence interval of 0.0003-0.0079. The successful identification of a resistance allele in a field collection of insects suggests that the F ₁ screening technique could be an effective tool for detecting and monitoring rare Bt-resistance alleles in field populations of D. saccharalis.