75.6 Saturday, Jan. 5 Developmental changes in tracheal system structure and function in the caterpillar, Manduca sexta GREENLEE, K. J.*; SOCHA, J. J.; EUBANKS, H. B.; LEE, W.-K.; KIRKTON, S. D.; North Dakota State University; Virginia Tech; Jackson State University; Argonne National Laboratory; Union College firstname.lastname@example.org
Abdominal pumping in caterpillars has only been documented during molting. Using synchrotron x-ray imaging and high-speed flow-through respirometry, we show that Manduca sexta caterpillars also 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. Abdominal pumping was only observed in larger, older caterpillars (> 0.2 g body mass), suggesting that the hypoxia response varies with ontogeny. In caterpillars that exhibited abdominal pumping, neither the frequency of compression nor the percent change in tracheal diameter varied with body mass, suggesting that there is a threshold for this behavior. 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, the diameters of the major tracheae either did not vary with body mass or did 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.