DISCONTINUOUS GAS-EXCHANGE IN INSECTS

Many insects exchange respiratory gases cyclically and discontinuously . A typical discontinuous gas exchange cycle (DGC) starts with a close d-spiracle (C) phase, during which little external gas exchange takes place, followed by a fluttering-spiracle (F) phase, which is usually d ominated by diffusive oxygen uptake. The DGC is terminated by an open- spiracle (O) phase, during which accumulated CO2 escapes. This review critically examines the applicability of the DGC to insect gas exchang e in general, discusses the primary mechanisms of gas exchange in the F and O phases, evaluates the widespread hypothesis that the DGC lower s respiratory water loss rates adaptively, and proposes new hypotheses concerning the evolutionary genesis of the DGC in insects and other t racheate arthropods.