Metabolic rate controls respiratory pattern in insects

The majority of scientific papers on the subject of respiratory patterns in insects have dealt with the discontinuous gas-exchange cycle (DGC). The DGC is characterized by the release of bursts of CO(2) from the insect, followed by extended periods of spiracular closure. Several hypotheses have been put forward to explain the evolutionary origin and physiological function of this unusual respiratory pattern. We expand upon one of these (the oxidative damage hypothesis) to explain not only the occurrence of the DGC but also the mechanistic basis for the transition to two other well-characterized respiratory patterns: the cyclic pattern and the continuous pattern. We propose that the specific pattern employed by the insect at any given time is a function of the amount of oxygen contained in the insect at the time of spiracular closure and the aerobic metabolic rate of the insect. Examples of each type of pattern are shown using the insect Rhodnius prolixus. In addition, contrary to the expectations deriving from the hygric hypothesis, it is demonstrated that the DGC does not cease in Rhodnius in humid air.