Eliminating host-mediated effects demonstrates Bt maize producing Cry1F has no adverse effects on the parasitoid Cotesia marginiventris

Abstract

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an important pest of maize in the United States and many tropical areas in the western hemisphere. In 2001, Herculex I(®) (Cry1F) maize was commercially planted in the United States to control Lepidoptera, including S. frugiperda. In 2006, a population of S. frugiperda was discovered in Puerto Rico that had evolved resistance to Cry1F maize in the field, making it the first well-documented case of an insect with field resistance to a plant producing protein from Bacillus thuringiensis (Bt). Using this resistant population, we conducted tri-trophic studies with a natural enemy of S. frugiperda. By using resistant S. frugiperda, we were able to overcome possible prey-mediated effects and avoid concerns about potential differences in laboratory- or field-derived Bt resistance. We used the Cry1F-resistant S. frugiperda to evaluate effects of Cry1F on Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a larval endoparasitoid of S. frugiperda, over five generations. Our results clearly demonstrate that Cry1F maize does not affect development, parasitism, survivorship, sex ratio, longevity or fecundity of C. marginiventris when they parasitize Cry1F maize-fed S. frugiperda. Furthermore, the level of Cry1F protein in the leaves was strongly diluted when transferred from Bt maize to S. frugiperda and was not detected in larvae, cocoons or adults of C. marginiventris. Our results refute previous reports of C. marginiventris being harmed by Bt proteins and suggest that such results were caused by prey-mediated effects due to using Bt-susceptible lepidopteran hosts.