The European corn borer, Ostrinia nubilalis (Hübner), is one of the most important insect pests of corn in the U.S. With the advent of corn hybrids expressing Bacillus thuringiensis genes, specific management strategies have been mandated to prevent or delay the development of resistance in target pest species. One aspect critical to the success of these resistance management strategies is understanding resistance genes inheritance. O. nubilalis colonies have been selected for resistance to the Bt Cry1Ab toxin in our laboratory for over 60 generations, having developed significant levels of resistance (up to 2200-fold). The objectives of this study were to determine whether resistance is sex-linked or autosomal, the degree of dominance, and the numbers of genes involved. Parental populations were established using standard rearing procedures. Two susceptible and two selected populations were used to establish reciprocal crosses between RR and SS parents. The F1 populations were backcrossed with SS parents. Pupae were arranged in cages so that RR males would mate with SS females, and vice-versa. Neonate larvae from these crosses were assayed for Cry1Ab susceptibility and compared to both parental strains. Results indicated that resistance was autosomal, incompletely dominant, and involved few genes. A preliminary study was also conducted to establish diagnostic concentrations of Cry1Ab to discriminate population genotypes based on their phenotype. These data will assist in the development of a tool for characterizing Cry1Ab resistance in the field.
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