Correlation of glutathione S-transferase and DDT dehydrochlorinase activities with DDT susceptibility in Anopheles and Culex mosquitos from northern Thailand

Abstract

Comparative DDT-susceptibility status as well as glutathione S-transferase activity and DDTase activity of Anopheles minimus (A), An. annuleris and Culex quinquefasciatus were investigated to ascertain the role of these enzymes in DDT-resistance. The standard WHO susceptibility test kits was used to discriminate between resistant and susceptible populations. GST activity was measured in microtiter plates whereas DDTase activity was determined by HPLC quantitation of DDT metabolites. This is the first report of DDT-resistance in the Thai malaria vector, An. minimus species A. A positive correlation of DDT-resistance and DDTase activity was observed in this species as well as in the suspected vector, An. annularis. However, GST activity was not correlated to DDT-resistance in either species. Statistical analysis and scatter plots demonstrated the non-correlation between DDTase and GST activity in An. annularis. Studies in Culex quinquefasciatus revealed difference in GST/ DDTase and the relationship to DDT-resistance compared to the anopheline species. The Culex GST activity is correlated to DDTase activity. These results suggested that a positive correlation of GST and DDTase activity might be species dependent.