RASCON, B*; HARRISON, JF; Arizona State University; Arizona State University: Atmospheric oxygen effects on metabolic rate and behavior of tethered flying locusts

Insects are known to exhibit a high tolerance to hypoxia. Prior studies have shown that the critical atmospheric P_O2 (P_c) for carbon dioxide emission for resting grasshoppers is less than 5 kPa, which suggests that the oxygen delivery capacity of the tracheal system is excessive in comparison to demand. Is it possible that this excess capacity exists to sustain activities that require higher oxygen fluxes such as flight? Alternatively, do increases in tracheal conductance allow even flying insects to have large safety margins for oxygen delivery? We tested the effect of atmospheric P_O2 on carbon dioxide emission during rest and flight, as well as on flight behavior, and lift production in tethered flying Schistocerca americana. We found that the P_c for carbon dioxide emission of resting grasshoppers was less than 1 kPa as in prior studies. The P_c for carbon dioxide emission during flight was 4 kPa, the P_c for flight bout duration was 15 kPa, and the P_c for lift production was 7.5 kPa. Calculations suggest that the P_c for steady-state oxygen consumption is between 10 and 21 kPa (much higher than for resting animals), and that tracheal oxygen stores allowed the brief flights in 5 and 10 kPa P_O2 atmospheres to occur. Thus, the excess oxygen delivery capacity observed in resting insects is partially eliminated during flight. However, tracheal conductance does increase substantially during flight, by a factor similar to that previously documented for ventilation. This research was partially supported by an NSF grant (IBN 9985857) awarded to JFH, a NIH grant awarded to the MARC Program at Arizona State University, and a grant awarded to JFH and BR through WAESO at Arizona State University.