Factors affecting the control of body volume in the larvae of the mosquitoes Aëdes aegypti (L.) and Aëdes detritus Edw.

Abstract

ABSTRACT Control of body volume has been studied in closely related freshwater and salt-water mosquito larvae (Aëdes aegypti and A. detritus). In A. aegypti osmotic inflow of water is equal to the rate of extrusion in urine and is less than the rate of production of Malpighian tubule fluid. Some of this fluid is conveyed to the rectum by intestinal peristalsis dependent on adequate hydrostatic pressure in the pyloric chamber, the rest is conveyed to the midgut by retroperistalses and is resorbed into the haemolymph. Retroperistalses are normally partly inhibited by nervous control probably involving the stomatogastric system and stretch receptors in the body wall. When inhibition is stopped (by interruption of the anterior part of the nerve cord) pressure in the pyloric chamber stays low, intestinal peristalses and hence urine production are curtailed, and the larvae swell. In A. detritus urine production is apparently independent of the slow osmosis and is balanced normally by drinking. Larvae with the mouth sealed shrink in consequence of urine output. Toleration of shrinkage is probably advantageous when the larvae are in concentrated brine.