Ontogenetic change in dietary selection for protein and lipid by gypsy moth larvae

Physiological changes during insect ontogeny should be manifest in changes in nutrient requirements and food preference. To investigate ontogenetic changes in food preference and digestive physiology, third- through sixth-instar gypsy moth larvae were provided choices among artificial diets differing in protein and lipid concentrations. Control larvae received two identical cubes of diet that were nutritionally complete, each containing a balanced mixture of protein and lipid. A second group of larvae received two different but complementary cubes, one deficient only in protein, the other deficient only in lipid. During early to late instars, preference shifted away from lipid-deficient, high protein cubes toward protein-deficient, high lipid cubes. This is consistent with the need for late-instar larvae to accrue energy reserves and specific fatty acids required during the pupal and non-feeding adult stages. Male larvae ate a higher proportion from the protein-deficient, high-lipid cube than females, possibly the result of greater energy demands by adult males. Female larvae tended to grow faster on deficient, complementary cubes than larvae provided complete cubes, despite poorer food utilization efficiency. These shifts and sex-specific variations in preference for protein and lipid likely reflect changing nutrient demands and fundamental physiological differences.