Diagnostic-dose bioassays are used to phenotypically classify O. nubilalis individuals as resistant or susceptible. However, if the goal of resistance monitoring is to monitor changes in the frequencies of resistance alleles, a better genetic understanding of potential resistance traits is necessary. Crosses of resistant and susceptible colonies of O. nubilalis were used to find doses of Cry1Ab that distinguished between resistant and susceptible phenotypes. The doses of Cry1Ab that best discriminated among the composite resistance phenotypes were incorporated into a genetic mapping project. The mapping of genetic factors will allow us to partition the composite resistance trait to regions of the O. nubilalis genome. The ultimate goal will be efficient bioassays and genetic assays that will allow genotyping of individuals for loci with the greatest probability of influencing resistance evolution in wild populations of O. nubilalis.