Fig. 8. Induced respiratory flow reversal causing CO₂ emission from the anterior spiracles (spiracles I) during flight of a male Manduca sexta (mass 1.4g, 10 days old). Results from a split-chamber experiment (see inset at the top of the figure) with stepwise pressure increases applied to the posterior chamber. CO₂ emission from the anterior spiracles (SpI) begins when the pressure difference P between the posterior chamber and the anterior chamber exceeds 25Pa. Sampling rate was 400Hz.