REGULATION OF RECTAL SECRETION IN SALINE-WATER MOSQUITO LARVAE LIVING IN WATERS OF DIVERSE IONIC COMPOSITION

  • 1 January 1977
    • journal article
    • research article
    • Vol. 66  (FEB) , 83-96
Abstract
Larvae of the saline-water mosquito Aedes campestris, were adapted to 3 waters, all having an osmotic concentration of 700 mOsm [milliosmoles], but differing in ionic ratios. The (Na + Mg)SO4 medium was much more toxic than the NaHCO3 or the NaCl media. Ionic and osmotic concentrations of hemolymph and rectal secretion were measured in larvae adapted to all 3 media. The ratio of ionic concentrations in the rectal secretion reflected those in the external medium to which the larvae had been adapted, with the exception of SO42- which was possibly replaced by HCO3- in the secretion. These differences in rectal fluid composition persisted even though all ligated recta were bathed in the same artificial hemolymph. The Malpighian tubules were the major site of SO42- excretion. In media containing high levels of Na+, Mg2+, K+, Cl- and HCO3-, the rectum secreted a hyperosmotic fluid containing these ions at concentrations several times greater than those in the hemolymph. These data provide the basis for speculation on the functioning of anal papillae in waters of diverse chemical composition.