| Summary: | 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.
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