Macronutrient Intake Alters the Susceptibility of Noctuid Pests to Bt Cotton

Insect resistance to Cry and Vip toxins derived from Bacillus thuringiensis (Bt) and expressed in transgenic crops is a major concern for the sustainability of Bt cotton. Therefore, accurate resistance monitoring assays are crucial for ensuring growers and industry stay one step ahead of the insect pests. Nutrition is a neglected factor in insect resistance monitoring, but recent results indicate that it can play a critical role in Helicoverpa zea’s ability to survive when exposed to Cry1Ac.  With concerns about the potential invasion of Helicoverpa armigera into the United States, we were interested in determining if the same pattern of nutritionally mediated susceptibility to Bt toxins that we see in H. zea is also present in other noctuid species. To do this, we first determined the macronutrient intake target (IT) for resistant and susceptible lines of two noctuid pests (H. armigera and H. punctigera). We then compared insect susceptibility to several Bt toxins at the optimal IT and a suboptimal rearing diet. The results of this study provide insights into differences in the expression of nutritionally mediated variation in susceptibility among helitothine species.