Hypoxia‐induced compression of the tracheal system in the caterpillar, Manduca sexta

Abstract

Abdominal pumping in caterpillars has only been documented during molting. Here, with synchrotron x‐ray imaging and high‐speed flow‐through respirometry, we show that Manduca sexta caterpillars contract their bodies in response to hypoxia, which results in significant compression of the tracheal system. Tracheal compression induced by abdominal contraction appears to be the driving force for external gas exchange, as evidenced by the high correlation between CO2 emission peaks and external body movements. Both frequency and diameter of tracheal compression increased with body mass as caterpillars increased in age. However, abdominal pumping was only observed in larger, older caterpillars (> 0.2 g body mass), suggesting that the hypoxia response varies with ontogeny. As insects increased in size, the fraction of tracheal system structures in the head increased, but not as much as would be predicted based on geometric scaling. The fraction of the body occupied by tracheae in the prothorax and last abdominal segment remain constant throughout ontogeny. Furthermore, diameter of major tracheae either do not vary with body mass or do not increase as much as expected, suggesting that trade‐offs between non‐respiratory structures result in smaller tracheae than would be expected based on geometric scaling. (Supported by NSF, NIH‐NCRR and US DOE)