Background/Question/Methods Transgenic crops expressing insecticidal crystal proteins from the bacterium Bacillus thuringiensis (Bt) have been commercialized worldwide to control lepidopteran pests since 1996.  This has imposed an unprecedented intense selection pressure on target pests that could result in field evolution of resistance to Bt crops.  Here we report a survey of resistance of several H. zea field populations to Cry1Ac and Cry2Ab by diet incorporation bioassay, leaf bioassay, greenhouse experiments, and genotyping of cadherin alleles by PCR gel analysis.

Results/Conclusions Several field strains of *H.zea* collected in 2008 showed reduced Bt susceptibility compared to susceptible strains in diet incorporation bioassays. They also showed higher survival on Bt cotton leaves. Partial cDNA and genomic DNA sequences of the cadherin gene have been cloned from both field and lab susceptible strains. Sequence alignment has identified some changes between the resistant and susceptible alleles. We are currently investigating if these changes contribute to reduction in the susceptibility of those field strains.