Oxygen partial pressure effects on metabolic rate and behavior of tethered flying locusts

Resting insects are extremely tolerant of hypoxia. However, oxygen requirements increase dramatically during flight. Does the critical atmospheric PO2 (Pc) increase strongly during flight, or does increased tracheal conductance allow even flying insects to possess large safety margins for oxygen delivery? We tested the effect of PO2 on resting and flying CO2 emission, as well as on flight behavior and vertical force production in flying locusts, Schistocerca americana. The Pc for CO2 emission of resting animals was less than 1 kPa, similar to prior studies. The Pc for flight bout duration was between 10 and 21 kPa, the Pc for vertical force production was between 3 and 5 kPa, and the Pc for CO2 emission was between 10 and 21 kPa. Our study suggests that the Pc for steady-state oxygen consumption is between 10 and 21 kPa (much higher than for resting animals), and that tracheal oxygen stores allowed brief flights in 5 and 10 kPa PO2 atmospheres to occur. Thus, Pc values strongly increased during flight, consistent with the hypothesis that the excess oxygen delivery capacity observed in resting insects is substantially reduced during flight.