Lighton, J. R. B.*; Turner, R. J.: WATER AND CARBON DIOXIDE FLUX IN THE FLUTTER PHASE OF THE INSECT DISCONTINUOUS GAS EXCHANGE CYCLE (DGC).

The insect DGC is characterized by extreme variations in carbon dioxide release and oxygen uptake rates. During the flutter or F phase of the DGC, oxygen diffuses inwards from a ca. 21 kPa external partial pressure to a ca. 4 kPa internal partial pressure. Is this process augmented by inward-directed bulk flow, caused by a negative trans-spiracular pressure gradient, as Kestler and others surmise? JRBL and others have shown that diffusive processes appear to be sufficient to explain experimental observations performed on F-phase carbon dioxide release. However, direct experimental evidence of F phase water vapor emission rates with reference to carbon dioxide release rates has been lacking because of the extreme sensitivity of the required measurements. These experimental measurements are important, because arguments for the evolution of the insect DGC that are based on restriction of respiratory water loss by the DGC, rather than the authors’ argument that the DGC is primarily an adaptation to gas exchange in hypoxic and hypercapnic conditions, depend vitally on the nature and balance of the diffusive and convective processes taking place during the F phase. In this study we reveal the first experimental data on F-phase water vapor release and discuss the implications of our findings for the diffusive model of the DGC’s F phase. NSF-BSR9306537, NSF-IBN9603873.