The effect of low atmospheric pressure on adult Aedes aegypti and on housefly pupae

Abstract

The mortality of the mosquito Aedes aegypti L. at low atmospheric pressure (below 1 6 atmosphere) is due to at least three factors acting independently: (1) desiccation; (2) lack of oxygen; (3) low pressure per se. The mortality was found higher at low air pressures than at atmospheric pressure of the same partial pressure of oxygen. An apparatus was designed for the measurement of respiration at very low atmospheric pressures; in order to minimize differences in activity, the oxygen uptake was measured at different oxygen tensions on haltere-less and decapitated mosquitoes. The oxygen uptake became oxygen-limited at a partial pressure of oxygen between 30 and 15 mm Hg, irrespective of whether this was obtained by decompression of air or at atmospheric pressure in an appropriate oxygen-nitrogen mixture. At the lowest pressure tested there appeared to be an effect of pressure on respiration over and above that caused by low oxygen tension. When the oxygen uptake was first measured at very low atmospheric pressures, and then again after the system was brought back to atmospheric pressure by adding nitrogen, there ensued a two- to four-fold increase. Very similar results were obtained with the pupa of the housefly Musca vicina Macq. in corresponding measurements of respiration. Changes in the opening time and aperture of the mosquito spiracles regulate the oxygen uptake under various total and partial gas pressures. This accounts for the effects of desiccation at low pressures.