How female caterpillars accumulate their nutrient reserves.

Female Lepidoptera are often heavier than males. We examined the importance of consumption and post-ingestive processing as mechanisms for female Heliothis virescens larvae to meet the protein and carbohydrate requirements. In experiments in which caterpillars had a choice of diets, enabling them to select an appropriate protein and carbohydrate intake, females caterpillars ate more carbohydrate than males, but only on the heavily carbohydrate biased treatment. Overall, the sexes were not distinguished according to the selective feeding behavior, but females accumulated more protein and carbohydrate over the whole instar than the males did. Additionally, when given no choice, females ate more than males and accumulated more protein provided the diet contained a high proportion of protein. If they were reared on a high carbohydrate diet, there were no differences between the sexes. Our results indicate that female H. virescens larvae accumulate protein by regulating both intake and post-ingestive processing on high protein foods. In the field, late instar H. virescens feed on anthers, which are protein-rich and have the highest amino acid content relative to other cotton floral tissues.