Mechanisms of Hemolymph Acid-Base Regulation in Aquatic Insects

Abstract

Insects are an important and abundant component of the aquatic habitat They are used as indicators of water quality and provide food for fish 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 are 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 respirator, systems have dezveloped within the aquatic insects to extract oxygen from water: water breathers, which use morphological gills; and air breathers, which obtain air from a bubble attached to the body or directly from the atmosphere. This article summarizes research to date pertaining to acid-base regulation in these two functional groups of aquatic insects and compares them with other aquatic ectotherms. Excretion appears capable of handling base removal in the feu alkaline-water-inhabiting species studied, and ion exchange mechanisms across the integumenzt may be involved in pH regulation of insects exposed to acid conditions. Future work should examine the use of respiratory processes in extracellular pH regulation to clarify the role dfferent tracheal systems play in insect acid-base balance. An understanding of the mechanisms involved in acid or alkali tolerance may help in the selection of species as bioindicators of water quality.