MECHANISMS OF HEMOLYMPH ACID-BASE REGULATION IN AQUATIC INSECTS

Insects are an important and abundant component of the aquatic habitat . They are used as indicators of water quality and provide food for fi sh and birds. The composition and abundance of insect assemblages are known to change with pH. The physiological mechanisms used by insects to cope with extreme environmental pH and regulate extracellular pH ar e virtually unknown. Evolutionarily, the movement into water from land has consequences with respect to gas transfer, as air has 20-40 times more oxygen per unit volume than water. Two functional respiratory sy stems have developed within the aquatic insects to extract oxygen from water: water breathers, which use morphological gills; and air breath ers, which obtain air from a bubble attached to the body or directly f rom the atmosphere. This article summarizes research to date pertainin g to acid-base regulation in these two functional groups of aquatic in sects and compares them with other aquatic ectotherms. Excretion appea rs capable of handling base removal in the few alkaline-water-inhabiti ng species studied, and ion exchange mechanisms across the integument may be involved in pH regulation of insects exposed to acid conditions . Future work should examine the use of respiratory processes in extra cellular pH regulation to clarify the role different tracheal systems play in insect acid-base balance. An understanding of the mechanisms i nvolved in acid or alkali tolerance may help in the selection of speci es as bioindicators of water quality.