Protein-carbohydrate regulation and nutritionally-mediated responses to Bt are affected by caterpillar population history.

BACKGROUND The widespread adoption of genetically modified crops, including Bt crops that target chewing insects, has transformed agricultural pest management. This increased use of Bt has raised concerns about the onset of resistance amongst target pests. Recent studies have shown that for some caterpillars, nutritional foraging, e.g. the ratio of proteins and carbohydrates consumed, can affect the insect susceptibility to the Bt toxin Cry1Ac. However, studies on both nutritional foraging and Bt susceptibility tend to rely on laboratory colonies without specifically addressing physiological differences that may occur between populations of the same species. Here, we used choice assays, no choice assays, and dose response assays to address two overarching questions. First, do populations of Spodoptera frugiperda (J.E. Smith) vary in their protein-carbohydrate foraging behavior? Second, does protein-carbohydrate intake impact S. frugiperda's susceptibility to the Bt toxin Cry1F. RESULTS All three of our S. frugiperda populations actively regulated their protein-carbohydrate intake, but we observed significant differences between populations with respect to their self-selected protein-carbohydrate intake. We also found that feeding at the protein-carbohydrate intake target slightly increased Cry1F susceptibility for one S. frugiperda population, but had no effect on the other two populations. CONCLUSIONS Our findings indicate that inherent differences exist in the nutritional physiology of three S. frugiperda populations, possibly related to the time spent in culture. This suggests population level differences are an important consideration when drawing parallels between field-collected and laboratory-reared insects. This article is protected by copyright. All rights reserved.