Dietary Effect on the Performance and Body Composition of the Generalist Insect Jerbivore, Heliothis virescens (Lepidoptera: Noctuidae)

All animals, including insect herbivores, eat to acquire nutrients that are essential for fueling physiological processes associated with growth, development, and reproduction. Protein and digestible carbohydrates are two nutrients required in large quantities by insect herbivores, but the amounts in which they occur in plants can be highly variable. In this thesis, I explore how the amounts and ratios of protein and digestible carbohydrate in an insect herbivore's food affect lifetime performance and body elemental composition. I do this by confining a generalist caterpillar, Heliothis virescens, to semi-synthetic foods with fixed protein-carbohydrate amounts and ratios. I show that foods with protein-carbohydrate ratios that match the self-selected protein-carbohydrate intake of final instar caterpillars correlate strongly with best performance, and that small deviations away from this optimal protein-carbohydrate ratio can result in large drop-offs in overall performance, particularly for males. I also show the importance of protein-carbohydrate balance over total macronutrient content. Finally, my results demonstrate that H. virescens caterpillars do not practice strict elemental homeostasis. My result, when contrasted with earlier work on caterpillars, suggests that hemimetabolous and holometabolous insect herbivores practice different degrees of elemental homeostasis.