Inhibition of strong midgut alkalinization in larval yellow fever mosquitoes (Aedes aegypti) with HEPES buffer

Abstract

Like some other larval insects, larval mosquitoes generate an extremely alkaline (pH 10–12) compartment in their anterior midgut. The mechanisms of midgut alkalinization are not completely understood. However, digestive enzymes are adapted to this high pH and it is believed that the alkaline environment increases nutrient assimilation. Because larval mosquitoes drink the medium, it could be anticipated that buffering the medium could prevent the animals from alkalinizing the anterior midgut. Alkalinization of the midgut can be studied by addition of the pH indicator m‐cresol purple to the medium and observing the color of the midgut. In larvae raised under control conditions the midguts showed a purple color, indicating midgut alkalinization. When maintained in water containing 25 mmol/l HEPES buffer midgut alkalinization was hardly detectable. When raising larvae in water containing 50 mmol/l HEPES, no alkalinization was observed. In buffered water, the development of larvae through the four instar stages was slower and many larvae did not reach the pupal stage. Financial support by the NIH (1R01AI063463‐01A2) and by a Wagner College Faculty Research Grant is gratefully acknowledged.