Strategies for regulation of hemolymph pH in acidic and alkaline water by the larval mosquitoAedes aegypti(L.) (Diptera; Culicidae)

Abstract

SUMMARYThe responses of larval Aedes aegypti to media of pH 4, 7 and 11 provide evidence for pH regulatory strategies. Drinking rates in pH 4 media were elevated 3- to 5-fold above those observed in pH 7 or 11. Total body water was elevated during acute exposure to acidic media. During chronic exposure, total body water was decreased and Malpighian tubule mitochondrial luminosity, quantified using Mitotracker Green FM, increased. Malpighian tubule secretion rates and energy demands thus appear to increase dramatically during acid exposure. In alkaline media, drinking rates were quite low. Larvae in pH 11 media excreted net acid (0.12 nequiv H+g–1 h–1) and the pH indicators azolitmin and bromothymol blue revealed that the rectal lumen is acidic in vivo at all ambient pH values. The anal papillae (AP) were found to be highly permeant to acid–base equivalents. Ambient pH influenced the length, and the mass-specific length, of the AP in the presence of NaCl (59.9 mmol l–1). In contrast, the length and mass-specific length of AP were not influenced by ambient pH in low NaCl conditions. Mitochondrial luminosity was reduced in AP of larvae reared in acidic media, and was not elevated in alkaline media, relative to that of larvae reared in neutral media. These data suggest that the AP may compromise acid–base balance in acidic media, and may also be an important site of trade-offs between H+ homeostasis and NaCl uptake in dilute, acidic media.