MALPIGHIAN TUBULES OF AEDES-AEGYPTI - 5 TUBULES, ONE FUNCTION

Urine formation in the yellow fever mosquito begins by secretion of Na , K, Cl and water in the distal, blind-ended portions of five Malpighi an tubules. The tubules appear structurally similar. To answer the que stion whether the tubules are also functionally similar, the transport activities of all five distal Malpighian tubules in each of eight mos quitoes were evaluated in vitro by measuring the rates of transepithel ial fluid secretion and the concentrations of Na, K and Cl in secreted fluid. Two-way analysis of variance revealed no differences between t he functions of distal tubules in a single mosquito but highly signifi cant differences between distal tubules from different mosquitoes. To confirm these results we repeated the experiment in mosquitoes placed on Na and K diets. Distal tubules isolated from mosquitoes on the Na a nd K diet respectively secreted significantly more Na and K than those of mosquitoes on the control diet. Two-way analysis of variance of th e data showed again no significant differences between tubules in a si ngle mosquito but significant differences between mosquitoes. We concl ude that the five distal Malpighian tubules present in the yellow feve r mosquito are functionally homogeneous. They display the properties o f a functional unit that responds in a unified fashion to meet the sal t and water problems of the animal.