Active Sodium and Chloride Transport by Anal Papillae of a Salt Water Mosquito Larva (Aedes campestris)

Abstract

ALTHOUGH anal papillae of freshwater mosquito larvae have been extensively investigated and shown to absorb actively sodium, potassium and chloride ions from the external medium^1–7, this organ has been assumed to have no function and an impermeable structure in salt water species^8,9. Considering insects in general, “in dilute external solutions the salt water larvae become hyperosmotic to the medium. Salt uptake mechanisms have yet to be demonstrated in these forms …”⁹. We wish to report the first evidence for extra-renal ion transport and regulation in the larva of a salt water insect (A. campestris). Initial experiments established that the salinity tolerance limits and the general pattern of ionic and osmotic regulation in fourth instar larvae of A. campestris are very similar to those of A. detritus, the only salt water mosquito previously studied in this context^3,8. In previous work there has been uncertainty about the attainment of steady states⁹ and we took these into account. When A. campestris larvae were transferred to tap water, 800 mmoles/l. of sodium chloride and solutions of intermediate concentration most change in blood ion concentrations and osmotic pressure occurred during the first day so that steady values were observed within 2 days.