Protein-Carbohydrate-Gossypol Regulation in Helicoverpa armigera and Its Consequences for Susceptibility to Bt Proteins

Helicoverpa armigera is a major pest of agricultural crops in the Old World and has recently been introduced to the New World. This caterpillar is highly polyphagous and notorious for developing resistance to many insecticides used for its control. Currently, Bt transgenic crops expressing insecticidal proteins are being used to control this caterpillar, but the evolution of resistance to Bt crops is always a concern. Generally caterpillars are confined to a single plant or row of plants during development, but there is enough nutritional variation between plant tissues within a plant that caterpillars have sufficient opportunity to balance their intake of key macronutrients (e.g. soluble protein and digestible carbohydrates). However, in addition to consuming Bt toxins, insect herbivores on Bt cotton also ingest secondary metabolites, namely gossypol. In our study, we used a nutritional geometry framework to assess H. armigera’s intake of protein and carbohydrate with and without gossypol in the diet. We then conducted dose response assays to assess the effects of diet protein carbohydrate profile and gossypol concentration on the insect’s susceptibility to two Bt toxins, Cry1Ac and Vip3Aa. Understanding how H. armigera’s feeding behavior with respect to nutrients and naturally occurring secondary metabolites can impact its susceptibility to Bt toxins can allow us to further explore the toxin’s mode of action, and create better resistant management strategies that could increase the sustainability of these transgenic technologies.