Hypotheses regarding the discontinuous gas exchange cycle (DGC) of insects.

The evolutionary origin of the insect respiratory pattern referred to as the discontinuous gas exchange cycle (DGC) has been a topic of extensive discussion among insect physiologists for at least 50 years. This pattern has often been thought to reduce respiratory water loss (RWL). However, because this pattern does not consistently conserve water among all taxa, other hypotheses have been proposed to try and explain the significance of the DGC. In this review we briefly describe the different hypotheses postulated to date. We conclude that the DGC is primarily a respiratory pattern deriving from the simultaneous regulation of O2 and CO2. It may nonetheless have additional adaptive functions in insects.