Ontogenetic changes in the body temperature of an insect herbivore

1. Over ontogeny, many insect larvae grow substantially, through at least several orders of magnitude in body size. Increasing size can profoundly change how individuals interact with their environments, by altering the opportunities for, and constraints on, feeding, changing the relative risk and sources of predation, and shifting the relative importance of physical factors in the environment. 2. Here I use eggs and larvae of Manduca sexta, which are herbivores on solanaceous plants in the southwestern US, to examine how body size affects body temperature. Larvae grow in excess of 10,000-fold by mass in a few weeks, from 0.001-g hatchlings to 12 – 15-g 5th-instar larvae. 3. Using infrared thermography, I show that increasing body size leads to large changes in body temperature: over ontogeny, average larval temperature increased by 3 – 7°C. The temperatures of eggs, hatchlings, and early larval instars were coupled to leaf temperatures (Datura wrightii), which were much cooler than amb...