Sodium regulation in the larvae of Chironomus dorsalis (Meig.) and Camptochironomus tentans (Fabr.): the effect of slat depletion and some observations on temperature changes.

Sodium regulation was studied in fourth instar larvae of Chironomus dorsalis and Camptochironomus tentans. Both maintain a body sodium level well above that of the surrounding medium. The haemolymph contains approximately 90% of total body sodium and approximates to a single compartment freely exchanging sodium with the external medium. The anal papillae play a primary role in sodium regulation, the gut being in secondary importance. Sodium regulation in both species is comparatively insensitive to alterations in acclimatization temperature. C. dorsalis and C. tentans are capable of maintaining sodium balance in media containing 10 mumole Na and 25 mumole Na respectively. When exposed to several changes of distilled water, C. tentansis capable of reducing sodium loss by elaboration of a more dilute urine. This is apparently,supplemented by a reduction in the permeability of the body surface. Activation of sodium uptake in both species is comparatively sluggish, with influx reaching a maximum only after the loss of greater than 30% body sodium.