[Metabolic resistance to organophosphate insecticides in Anopheles aquasalis Curry 1932, Libertador municipality, Sucre State, Venezuela].

A study of insecticide resistance was undertaken at focal level in the localities Catuaro, Guayana, Platanito and Rio de Agua, Libertador County, Sucre State, Venezuela, a region with malaria transmission, where Anopheles aquasalis is the main vector. Insecticide resistance was assessed in the organophosphate insecticides fenitrothion and pirimiphos methyl, both of which are used in the control of Anopheles aquasalis. In adult mosquitoes, biological tests were performed and identification of resistance mechanisms in vitro by biochemical tests. Elevated levels of alpha and beta esterases were detected, as well as altered acetylcholinesterase activity. Multifunction oxidase enzymes in populations of Anopheles aquasalis in three of the locations evaluated were also altered; therefore, both enzyme systems may be involved in the expression of resistance to organophosphate insecticides in the study populations. The enzyme activity of glutathione-S-transferase was noted only in Rio de Agua. A better understanding of the resistance to insecticides was obtained in this species of medical importance. These findings will assist the implementation the practice of insecticide rotation as a strategy within an integrated management program.