Fig. 3. Intratracheal pressure relative to atmospheric pressure during shivering (A) and steady flight (B) in tethered Manduca sexta. During shivering, the mean pressure is approximately equal to atmospheric pressure (0Pa on this scale). During flight, the mean pressure at the anterior spiracles (SpI, horizontal broken line) is negative, whereas that at the mesoscutellar air sac (ScutII, horizontal thick line) is positive. The inset moth pictures show wing position and wingbeat amplitude. Sampling rate was 40kHz.