Mass and volume growth of an insect tracheal system within a single instar.

Organisms must accommodate oxygen delivery to developing tissues as body mass increases during growth. In insects, the growth of the respiratory system has been assumed to occur only during molts, whereas body mass and volume increase during the larval stages between molts. This decouples whole-body growth from the growth of the oxygen supply system. This assumption is derived from the observation that the insect respiratory system is an invagination of the exoskeleton, which must be shed during molts for continued growth to occur. Here, we provide evidence that this assumption is incorrect. We found that the respiratory system increases substantially in both mass and volume within the last larval instar of Manduca sexta larvae, and that the growth of the respiratory system changes with diet quality, potentially as a consequence of shifting metabolic demands.