Macronutrient Availability Alters Susceptibility of Helicoverpa Zea (Lepidoptera: Noctuidae) to Helicoverpa Armigera Nucleopolyhedrovirus

Helicoverpa armigera nucleopolyhedrovirus (HearNPV) can be used as an alternative control tactic for Helicoverpa zea larvae in cotton, soybean, sorghum, and corn. However, control efficacy can vary significantly from one application to another. One potential explanation is variation in dietary macronutrient content across and even within crops. The objective of this research was to determine if altering the macronutrient intake of H. zea larvae affected their susceptibility to HearNPV. This was done by rearing from hatch 1^st and 3^rd instar larvae on seven different artificial diets with varying ratios of protein (p) to carbohydrates (c) (35p:7c, 28p:14c, 26p:16c, 21p:21c, 16p:26c, 14p:28c, and 7p:35c). First instars were given contaminated diet 24 hours after hatch, while 3^rd instars were inoculated with contaminated diet upon molting. All larvae were given 24 hours to consume the infected diet; however, 1^st instars never consumed the entire diet cubes. Both a no-choice assay and a choice assay were conducted. Larvae were reared at 25˚C, 16L:10D and 70% humidity and monitored daily for mortality or pupation. Kaplan-Meier survival curves were constructed and all diet combinations were analyzed for significant differences. Neonates consuming higher protein diets exhibited longer survival, while those fed diets with lower protein had shorter survival times than more balanced diets, indicating that insect nutritional state can affect viral susceptibility. However, 3^rd instars exhibited the opposite effect. Larvae consuming carbohydrate-biased diets survived longer than larvae consuming protein-biased diets, implying the potential for developmental variation in nutritionally-mediated immune response and susceptibility based on larval stage.