OJEDA-AVILA, T; WOODS, HA; RAGUSO, RA: Effects of dietary variation on growth, composition, and maturation of Manduca sexta

Most experimental studies linking dietary variation with insect fitness have focused narrowly on single dietary ingredients and late larval growth. We examined the effects of variation in multiple dietary factors over most life stages of the sphingid moth, Manduca sexta. Larvae were reared on tobacco leaves and on artificial diets in which we varied three primary macronutrients; protein, sugar, and water. Larvae on control and low-sugar diets grew most rapidly and attained the largest pupal and adult sizes. Larvae reared on tobacco leaves grew rapidly in early instars, but slowed dramatically in the fifth, attaining the smallest final sizes. In contrast, larvae on low-water diet grew slowly in early instars, but rapidly in the fifth, ultimately attaining pupal and adult sizes nearly as large as control animals. This switch suggests that inadequate dietary water content may be more important for early than late instars, whereas components of the natural diet, possibly allelochemicals, have a greater negative effect on later instars when 90% of lifetime food biomass is ingested. We also measured fat content in each stage. Larvae given any artificial diet showed increasing fat content throughout all stages; those given tobacco had much lower fat contents, with only modest increases during the fifth instar and decreases in the pupal and adult stages. These data suggest that artificial diets provide a rich food source and may result in pupae and adults with abnormally high fat content. The converse view is that larvae eating tobacco may routinely experience carbohydrate and fat shortages, resulting in extremely lean pupae and adults. These differences are likely to have strong effects on adult physiology, reproduction, and foraging patterns.