65 - 75 Kar SK.pmd

In the present study, the feeding stage, body parts, development and sex specific activity of Glutathione S-transferases (GSTs) were observed in different mosquito species (Aedes aegypti, Culex quinquefasciatus, Anopheles stephensi, An. culicifacies, An. annularis, An. subpictus, An. vagus). GST activity was assayed spectrophotometrically at 23°C, using a UV Max microplate Reader, to measure the rate of conjugation of GSH to CDNB. A significant species-specific difference in the activity of GST was noticed, highest being in unfed Ae. aegypti (41.2 nmol/min/mg) followed by unfed Cx. quinquefasciatus (7.9 nmol/min/mg) and the least in unfed An. stephensi (5.8 nmol/min/mg). In all the species the GST activity was found to be significantly higher in fully fed and gravid stages compared with the unfed, while the enzyme activity was reduced after egg laying either to the level of unfed animals or well below its level in all the experimental species. The GST activity was found to be higher in the abdominal region of all the experimental species in comparison with the other body parts (head and thorax). The GST activity of An. stephensi increased gradually through the larval stages and reached the maximum level in the pupae and remained at that level in the newly emerged adults. However, its activity declined markedly (10 fold) with ageing from 5 to 40 days. A significant sex-related difference in the specific activity of GST was found in An. stephensi where approximately 3.5 fold lower activity was observed in males compared with its females, whereas no significant variation was noticed in Ae. aegypti and Cx. quinquefasciatus. The study corroborates the fact that GSTs are differentially regulated by multiple mechanisms in response to xenobiotics modulation in situation-specific manner such as species, sex, feeding and developmental stage. The knowledge of situation-specific modulation of GST will provide a better understanding of GST based insecticide resistance mechanism which is essential for the design of sensitive monitoring methods and for an effective insecticide resistance management. The findings are significant in terms of the methods used to control mosquito vector population.