The sugarcane borer,Diatraea saccharalis (F.),is a major maize borer pest and a target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the mid-southe region of the United States.Evolution of resistance in target pest populations is a great threat to the long-term efficacy of Bt crops.In this study,we compared the genetic basis of resistance to CrylAb protein in 3 resistant colonies of sugarcane borer established from field populations in Louisiana,USA.Responses of larvae to the Cry lAb protein for the parental and 10 other cross colonies were assayed in a diet-incorporated bioassay.All 3 resistant colonies were highly resistant to the CrylAb protein with a resistance ratio of ＞ 5 5 5.6 fold.No mateal effect or sex linkage was evident for the resistance in the 3 colonies;and the resistance was functionally nonrecessive at the CrylAb concentrations of ＜ 3.16 μg/g,but it became recessive at ＞10 μg/g.In an interstrain complementation test for allelism,the F1 progeny from crosses between any 2 of the 3 resistant colonies exhibited the similar resistance levels as their parental colonies,indicating that the 3 colonies most likely shared a locus of CrylAb resistance.Results generated from this study should provide useful information in developing effective strategies for managing Bt resistance in the insect.