BRADLEY,T.J.: The Discontinuous Gas Exchange Cycle in Insects May Serve to Reduce Oxygen Supply to the Tissues

The discontinuous gas exchange cycle (DGC) in insects, consists of a closed phase (C) during which the spiracular valves at the openings of the tracheae are closed, a flutter phase (F) when the spiracles open and close rapidly, and an open phase (O) in which the spiracles are open, allowing the free exchange of respiratory gases between the tracheal lumen and the outside air. Early workers such as Buck and Levy & Schneiderman, suggested that the DGC serves to reduce respiratory water loss. More recently, Lighton has suggested that the DGC serves to increase internal carbon dioxide concentrations, thereby facilitating the release of carbon dioxide into environments, such as underground burrows, which are rich in this gas. We have been conducting studies using the Hemipteran Rhodnius prolixus, an insect that takes a bloodmeal up to ten times its previous body volume. In the days following feeding, the insect remains completely still, yet its metabolic rate increases up to 14-fold. We have been using this unusual behavior to examine the effects of metabolic rate on the DGC. We found that the spiracles appear to close very tightly when metabolic rates are low, but do not close fully when the rates are higher. We will present data from other laboratories that demonstrate similar effects when metabolic rate is varied by temperature or when oxygen tensions are manipulated. I propose that the DGC may serve to reduce the supply of oxygen to the tissues during periods of low metabolic rate. Oxygen is toxic to cells, even at ambient concentrations, and insects may use the DGC to provide adequate gas exchange while reducing oxidative damage to tissues during periods of reduced oxygen demand. Supported by NSF grant IBN 0079501.