Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/24/2008
Publication Date: 4/1/2009
Citation: Prasifka, J.R., Hellmich II, R.L., Sumerford, D.V., Siegfried, B.D. 2009. Bacillus thuringiensis Resistance Influences European Corn Borer (Lepidoptera: Crambidae) Larval Behavior after Exposure to Cry1Ab. Journal of Economic Entomology. 102(2):781-787. Interpretive Summary: Behaviors of insects, including movement and mating, have been recognized as important factors that can influence how fast resistance to transgenic Bacillus thuringiensis (Bt) crops is likely to develop in the field. However, it is often unknown whether insects with genes that contribute to resistance behave differently than insects without such resistance genes. Laboratory tests were used to test whether genes for resistance to the Bt toxin Cry1Ab influenced how larvae (caterpillars) of the European corn borer behaved after feeding on the toxin. When only diet with Cry1Ab was available, larvae with one or two copies of resistance genes fed on Cry1Ab diet more than larvae without resistance genes. When larvae had a choice of diet with or without Cry1Ab, more larvae with one or two copies of resistance genes were found on the Cry1Ab diet. This suggests that resistant colonies developed in the laboratory do not show a greater ability to avoid toxins (called "behavioral resistance") than susceptible corn borers. This information is useful for industry, government, and academic stakeholders interested in delaying the evolution of resistance to Bt crops using mandatory insect resistance management plans.
Technical Abstract: The behavior of target pests has been recognized as an important factor to appropriately define resistance management plans for Bacillus thuringiensis (Bt) crops. However, most data available do not include the possible impact resistance alleles may have on the behavior of pest larvae or adults. To examine whether resistance (R) alleles influence behavior of European corn borer (Ostrinia nubilalis) neonates after exposure to dietary Cry1Ab, the responses of resistant (RR), susceptible (SS), and F1 progeny (RS) from two groups of resistant colonies were compared in laboratory tests using artificial diet mixed with 10–50% Cry1Ab or non-Bt isoline corn tissue. In no-choice tests, RR (and some RS) phenotypes were less likely to be irritated by Cry1Ab than SS larvae after 48 h of exposure to diets containing 10–50% leaf tissue. For a short period (less than or equal to 8 h), neonate O. nubilalis also appeared more likely to move off of diets that contained 10% non-Bt tissue when compared to diets with 25 or 50% non-Bt tissue. In agreement with results from no-choice tests, choice tests with 10 or 25% tissue indicated behavior of larvae with R alleles increased neonates exposure to Cry1Ab. For both tests, relative differences between phenotypes appeared dependent on the amount of Cry1Ab tissue incorporated into diets. Results suggest differences in behavior are a result of reduced physiological susceptibility to Cry1Ab, rather than an independent behavioral component to resistance. To provide useful data for resistance management plans, the effects of R alleles on movement and survival will need to be assessed using on-plant tests with resistant colonies.