Bacillus thuringiensis Resistance Influences European Corn Borer (Lepidoptera: Crambidae) Larval Behavior After Exposure to Cry1Ab

The behavior of pests targeted by Bacillus thuringiensis (Bt) crops has been recognized as an important factor to define resistance management plans. However, most data do not include the possible impact resistance may have on the behavior of pests. To examine whether resistance influences behavior of European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), neonates after exposure to dietary Bt, the responses of Cry1Ab-resistant, -susceptible, and hybrid (F1) lines from two populations were compared in laboratory tests by using artificial diet mixed with 10-50% Cry1Ab or non-Bt isoline corn, Zea mays L., tissue. In no-choice tests, resistant (and usually hybrid) lines were less likely to be irritated (i.e., to move away after physical contact with diet containing Cry1Ab) than susceptible larvae after exposure to diets containing 10-50% Cry1Ab leaf tissue. Early in the no-choice tests (8 h), neonate O. nubilalis also were more likely to move off of diets that contained 10% non-Bt tissue compared with diets with 25 or 50% non-Bt tissue. In agreement with results from no-choice tests, choice tests with 10 or 25% tissue indicated that resistant (and sometimes hybrid) larvae were more likely than susceptible neonates to be found on diet with Cry1Ab. For choice tests, differences among lines seemed dependent on the amount of Cry1Ab tissue incorporated into diets. Results suggest differences in behavior are a result of reduced physiological susceptibility to Cry1Ab and are not an independent behavioral component to resistance.