Dr. Siva R. M. Jakka from Iowa State University's Department of Entomology will be presenting this research as a part of the spring semester seminar series. This seminar will be located in E164 Lagomarcino Hall.
Abstract: Transgenic Bt corn hybrids expressing insecticidal toxins from Bacillus thuringiensis (Bt) have been increasingly planted to manage insect pests. The high adoption of Bt-based insecticidal technologies increases selection pressure for the evolution of resistance in insect populations. Development of field-evolved resistance was reported in fall armyworm, Spodoptera frugiperda (J. E. Smith), to Cry1Fa in cornfields in Puerto Rico and in western corn rootworm, Diabrotica virgifera virgifera (LeConte), to Cry3Bb1 in cornfields in Iowa. My research has been focused on the characterization of Bt resistance in fall armyworm and western corn rootworm to Bt corn hybrids. Our laboratory experiments indicated high levels of resistance to Cry1Fa in fall armyworm with recessive and autosomal mode inheritance. Cross-resistance studies with resistance larvae showed reduced susceptibility to Cry1Ab and Cry1Ac toxins and no cross-resistance to Cry1Ca toxin and Bt formulations. The lack of fitness costs in resistant fall armyworm was also supported by stable resistance. Binding experiments showed the modification of a common Cry1Fa-Cry1A toxin binding site is responsible for Bt resistance in fall armyworm. Comparison of receptor protein levels revealed reduced alkaline phosphatase (ALP) levels in resistant larvae and this reduced expression of ALP phenotype was linked to Cry1Fa resistance in fall armyworm. Bioassay results of western corn rootworm indicated high levels of resistance to corn expressing Cry3Bb1 toxin. These populations also showed positive cross-resistance among Cry3Bb1 and mCry3A toxins and no cross-resistance to Cry34/35Ab1 toxin. Results of these studies will help in understanding resistance mechanisms responsible for field-level resistance and formulate improved resistance management practices.