Pteridine fluorescence for age determination of Anopheles mosquitoes

The age structure of mosquito populations is of great relevance to understa nding the dynamics of disease transmission and in monitoring the success of control operations. Unfortunately, the ovarian dissection methods currentl y available for determining the age of adult mosquitoes are technically dif ficult, slow and may be of limited value, because the proportion of diagnos tic ovarioles in the ovary declines with age. By means of reversed-phase HP LC this study investigated the malaria vectors Anopheles gambiae and An, st ephensi to see if changes in fluorescent pteridine pigments, which have bee n used in other insects to determine the age of field-caught individuals, m ay be useful for age determination in mosquitoes. Whole body fluorescence w as inversely proportional to age (P < 0.001, r(2) > 91%) up to 30 days post emergence, with the regression values: y = 40580-706x for An. gambiae, and y = 52896-681x for An, stephensi. In both species the main pteridines were 6-biopterin, pterin-6-carboxylic acid and an unidentified fluorescent compo und. An. gambiae had only 50-70% as much fluorescence as An, Stephensi, and fluorescent compounds were relatively more concentrated in the bead than i n the thorax (ratios 1:0.8 An. gambiae; 1:0.5 An. stephensi). The results o f this laboratory study are encouraging. It seems feasible that this simple r and faster technique of fluorescence quantification could yield results o f equivalent accuracy to the interpretation of ovarian dissection. A double -blind field trial comparing the accuracy of this technique to marked, rele ased and recaptured mosquitoes is required to test the usefulness of the pt eridine method in the field.