Patterns and mechanisms of air flow during abdominal pumping in the grasshopper, Schistocerca americana

Abstract

While it has long been clear that convection (not diffusion) is the dominant mechanism for gas exchange in grasshoppers and other large insects, the patterns and mechanisms of air flow within insects remain poorly understood. Based on prior work by Weis‐ Fogh, Miller and Harrison it is believed that air flow in resting grasshoppers enters via the thoracic spiracles, flows longitudinally through the body along the gut, heart, nerve cord and spiracles, and exits primarily via the most terminal spiracles. We used synchrotron x‐ray imaging, high speed video and direct observation of spiracles to understand the patterns and mechanisms of abdominal air flow in the American locust, Schistocerca americana. We found that the abdomen contains collapsible air sacs and tracheae, as well as noncollapsible tracheae. During abdominal pumping, the viscera move anteriorly relative to the spiracles, contributing to compression of the air sacs and some of the tracheae, with others remaining open to allow air flow. In contrast to prior reports, the most caudal spiracles are mostly closed, opening briefly before air sac compression. An anteriorly‐directed compression wave and the timing of opening of the spiracles suggests that expiratory air flow is primarily forward‐directed within the abdomen, exiting via the first abdominal spiracles. Funded by NSF 0938047.