Diuresis in newly emerged, unfed mosquitoes. I. Fluid loss in normal females and males during the first 20 hours of adult life

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Abstract
Unfed mosquitoes (Aedes aegypti) decapitated soon after emergence from the pupa survive better than those decapitated later. In a test involving more than 700 females and more than 600 males, 80% of the mosquitoes decapitated during the first hour of adult life survived a period of 45 h post emergence (p.e.), whereas about 80% of those decapitated at 12 h or later failed to survive the same period. There was a linear fall in the rate of survival between 1 and 10 h p.e., after which the rate fluctuated between 10 and 30%. The mechanism accounting for this phenomenon seemed most likely to be loss of fluid under the control of a diuretic hormone released from the head, early decapitation protecting the insects from excess loss of fluid. To test this explanation the rate of excretion was measured in normal unfed moquitoes at regular intervals during the first 20 h of adult life. In females the rate of excretion was shown to rise from 10 nl min$^{-1}$ during the first hour of adult life to reach 27 nl min$^{-1}$ 12 h later. In males the rate of excretion fell from 7 to 5 nl min$^{-1}$ during the first 3 h before rising to 12 nl min$^{-1}$ by 9 h p.e. The rate of excretion decreased in both sexes from 15-16 h onwards. Newly emerged mosquitoes thus increase their preparedness for flight by loss of water through enhanced excretion during the first day.