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In order to determine whether proline can be utilized as fuel during flight of Aedes aegypti, proline, alanine, and glutamine concentrations were monitored at 0, 30 and 60 min after flight using sugar-fed males and females, and blood meal-fed females. In sugar-fed and blood meal-fed females, flight lead to a significant decrease in proline and a significant increase in glutamine concentration in both hemolymph and thorax. Only during flight after a blood meal was a significant increase in the alanine concentration observed in hemolymph. After flight, the proline alanine and glutamine levels in the hemolymph and thorax from males did not change significantly. In addition, activities of enzymes related to amino acid metabolism were assayed in homogenates of cephalothorax and thorax from both sexes, and in fat body and midgut from females. In both sexes, the activities of all the enzymes studied were significantly higher in thorax than in cephalothorax. The levels of the enzymes involved in proline oxidation were higher in thorax than in fat body and midgut. These results suggest that proline can be used as an energy substrate for flight muscle of Ae. aegypti females. However, the elevation in glutamine levels observed in hemolymph and thorax after flight has not been reported in other insects that fuel flight using proline and may suggest an additional mechanism for shuttling ammonia between flight muscle and fat body is present in mosquitoes.

1. Optimum conditions were established for determining the activities of the NADP(+)-linked enzymes, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase, in mosquito tissues. 2. The activity of each dehydrogenase was determined in samples of mosquitoes of different ages throughout the life-span. The specific-activity curves attained maximal values in the pupal or early adult period. From these maxima an 81% decrease in glucose 6-phosphate-dehydrogenase and 67% decrease in 6-phosphogluconate-dehydrogenase activities occurred after the tenth day of adult life; a 77% decrease in isocitrate-dehydrogenase activity occurred before the fifth day. 3. The activity differences were found in different body regions as well as in whole organisms. 4. Starvation of the larva or adult did not result in decreases in enzyme activity. 5. These findings support the hypothesis that the activities of enzymes that form NADPH are related to the biosynthetic activity, for the enzyme activities increased during the period of cellular growth and decreased during the aging period.