HARRISON, J.F.; LAFRENIERE, J.; HARTUNG, D.A.; GREENLEE, K.; KIRKTON, S.D.: Ontogeny effects on the diffusive and convective conductance of abdominal and leg trachea in Schistocerca americana grasshoppers

Several authors have proposed that evolution of gigantic insects in the late Paleozoic may have been made possible by atmospheric hyperoxia. Is there any evidence from extant insects that larger insects have more difficulty with oxygen delivery? In this study, we examined the morphology of the abdominal and leg trachea of grasshoppers of various size/age classes. In general, the ratio of diffusive capacity to oxygen consumption decreased with age. Diffusive gas exchange is particularly problematic for the leg. In contrast, for both the abdominal and leg trachea, increases in tracheal convective capacity tend to parallel increases in oxygen consumption. These morphological measures suggest that use of convection may allow insects to grow to larger sizes; whether this strategy becomes ineffective at some very large size remains to be seen.