The Effects of Diet Quantity on Developmental Plasticity of Size and Flight Energetics in the Hawk Moth Manduca sexta

AbstractThe energy needed for insect flight varies with the size and body proportions of different species or individuals. Wingbeat frequency during flight usually decreases as size increases, though these changes depend on the proportions of the wings and flight muscles. Metabolic rate during flight often changes with wingbeat frequency. Nutrition during development plays a key role in determining an individual's size and body proportions. We used an intermittent feeding regime during the fifth larval instar of the hawk moth (Manduca sexta) to investigate how nutrition-induced size variation affects flight capacity and energetics. Adult body mass decreased with more severe intermittent feeding, widening the range of body mass variation to nearly fivefold. Changes in body mass influenced body proportions through allometric effects, with wing area and thorax mass scaling hypoallometrically, while abdomen mass scaled hyperallometrically. Sex and nutritional treatment further influenced these relationships. The flight wingbeat frequency increased in smaller-sized individuals, and the thorax mass-specific metabolic rate was higher. Smaller individuals from the intermittent feeding treatment also showed a lower flight success, apparently due to a lower thorax-to-abdomen mass ratio. Flight muscle metabolic enzyme activities did not differ with size or nutritional treatment. Overall, changes in body mass and proportions resulting from developmental plasticity influence flight energetics, leading to compromises in flight energy demands and success without notably altering flight muscle metabolic phenotypes, which could restrict muscle power during flight.