HARRISON, J.F.; GREENLEE, K.J.; KIRKTON, S.D.; Arizona State University; Arizona State University; Arizona State University: Ontogeny of tracheal system function in insects

The amazing diversity of insect respiratory systems and their range of morphological and physiological changes during development challenge our ability to describe tracheal development with simple generalities. However, one clear pattern is an increase in aerobic scope during insect ontogeny. Aerobic scopes in flying adult insects far exceed those of running or crawling larval forms. The increases in maximal aerobic metabolic rates are correlated with increases in tracheal dimensions, tracheole and mitochondrial densities, and, in some insects, increases in number or size of air sacs. A second ontogenetic pattern is that responses of individuals to oxygen seem likely to transition from primarily morphological to physiological. For insect eggs, the morphology of the eggshell and chemistry of the underlying layers seem likely to determine oxygen delivery capacity, with little opportunity for physiological regulation. In larval fruitflies and mealworms there is evidence for compensatory regulation of tracheal morphology by atmospheric oxygen. Physiological mechanisms for controlling gas exchange appear in the larval stages and include control of spiracular opening and convection. At least in grasshoppers, physiological responses to hypoxia (ventilation frequency, tidal volume, coordination of spiracles with abdominal pumping) increase strongly during ontogeny. A third ontogenetic pattern is that the gas exchange system is likely to be increasingly challenged within each molt period. The scope for oxygen delivery decreases within instars for both resting and jumping grasshoppers. These within-molt patterns seem likely to be general for insects and perhaps animals with exoskeletons, as increases in body mass compress air sacs and increase oxygen demand despite little compensatory change in respiratory system morphology.