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

The behavior of pests targeted byBacillus thuringiensis (Bt) crops has been recognized as an important factor to deÞne resistance management plans. However, most data do not include the possible impact resistance may have on the behavior of pests. To examine whether resistance inßuences behavior of European corn borer,Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), neonates after exposure to dietaryBt, the responses ofCry1Ab-resistant, -susceptible, andhybrid (F1) lines from two populations were compared in laboratory tests by using artiÞcial diet mixed with 10Ð50% 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 10Ð50% 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 comparedwith dietswith 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 sometimeshybrid) larvaeweremore likely than susceptibleneonates tobe foundondietwithCry1Ab. 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.