Fitness costs of the Cry1A.105/Cry2Ab2-single and dual-gene resistance in Helicoverpa zea on non-Bt diet

Abstract: Corn earworm, Helicoverpa zea, is one of the most destructive agricultural pests targeted by Bt crops. Cry1A.105 and Cry2Ab2 are two common Bt proteins expressed in the Bt corn event MON 89034 to control some lepidopteran pests including H. zea. In this study, performance of a susceptible, a Cry1A.105-resistant, a Cry2Ab2-resistant, and a Cry1A.105/Cry2Ab2 dual-gene resistant strains, along with three F1 heterozygous genotypes, was assayed on non-Bt diet. The three F1 genotypes were established by crossing the susceptible insect with each of the three resistant strains. The objective of the study was to determine if fitness costs were associated with the resistances. Biological parameters measured for each insect strain/genotype were 9-day larval body weight, pupal body weight, neonate-to-adult survival and development, sex ratio, and progeny production. A few variations in some biological parameters were observed among insect strains/genotype, but the results generally showed that fitness costs were not associated with either the single- or dual-gene resistance in the test conditions. The lack of fitness costs of the single- or dual-gene resistance might be an important factor that has contributed to the recent widely occurred resistance in field populations of H. zea to Cry1A/Cry2A crops in the United States.