Involvement of mono-oxygenases as a major mechanism of deltamethrin-resistance in larvae of three species of mosquitoes.

Role of mono-oxygenases as a mechanism of resistance to the synthetic pyrethroid, deltamethrin in the larvae of Culex quinquefasciatus Say, Aedes aegypti L. and Anopheles stephensi Liston developed by laboratory selections with deltamethrin, DDT or deltamethrin and the synergist, piperonyl butoxide (PBO) in the ratio of 1:5, was investigated. There was a significant correlation with mono-oxygenase activity and larval LC50 to deltamethrin in various strains of all the three species. In addition, the activity of glucose-6-phosphate dehydrogenase (G6PD), the main NADPH generating enzyme for mono-oxygenases, also showed enhanced activity in deltamethrin and DDT-selected strains. The present data, therefore, clearly suggest that deltamethrin resistance in the larvae of Cx. quinquefasciatus, Ae. aegypti and An. stephensi is mainly due to the detoxification of deltamethrin by microsomal mono-oxygenases. High activity of G6PD observed in DDT-selected strains seems to be related to its role as a rate-limiting enzyme in GSH-dependent dehydrochlorination of DDT.