Assuntos
Animais , DDT/farmacologia , Humanos , Malária/prevenção & controle , Controle de MosquitosRESUMO
Involvement of esterase-mediated hydrolysis as a mechanism of pyrethroidresistance in three species of mosquitoes, viz., Aedes aegypti, Culex quinquefasciatus and Anopheles Stephensi was investigated by microplate assay of β-esterases in individual larva and adult female and male mosquitoes. Assuming an absorbance value of 0·4 and above at 555 nm as the threshold level of elevated esterase activity which confers resistance, frequency distributions of such individual test mosquitoes were constructed in resistant and susceptible populations. The results indicate the involvement of ester hydrolysis of Pyrethroids as a predominant mechanism of pyrethroid-resistance in the larvae of Culex quinquefasciatus but not in Aedes aegypti. However, a marginal role of esterases is indicated in the larvae of Anopheles stephensi.
RESUMO
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.