Control of the Respiratory Pattern in Insects

Abstract

Three respiratory patterns have been described in insects: Discontinuous, Cyclic and Continuous. The Discontinuous Gas Exchange Cycle (DGC) can be distinguished by the presence of an open phase in which the spiracular valves are fully open, a closed phase during which oxygen concentrations at the tissues are lowered, thereby reducing oxidative damage, and a flutter phase in which the spiracles open intermittently for very brief periods,. The flutter phase serves to regulate internal oxygen levels at a physiologically safe level. In the Cyclic pattern, the spiracles apparently never fully close, yet a rhythmic pattern of carbon dioxide release is observed. In the Continuous pattern, no rhythmicity can be discerned and carbon dioxide release is relatively constant. In this paper I provide evidence that the three patterns described above are not distinct, but rather are a continuum. The critical parameters influencing the pattern are 1) the partial pressure of oxygen in the surrounding atmosphere, and 2) the rate of oxygen use i.e. the aerobic metabolic rate. Insects exhibit the DGC when the tracheal system is capable of delivering oxygen during the open phase at a rate faster than it is consumed by oxidative metabolism. The minute to minute balance between these two processes, one delivering oxygen the other removing it, determines the pattern of respiration exhibited by the insect at any given time.