[Evaluation of the residual effect of pyrethroids on Anopheles in the Brazilian Amazon].

OBJECTIVE: To evaluate the residual effect of pyrethroids on the mortality rates of Anopheles in order to check their efficacy in indoor residual spraying in the Amazon Region, Brazil.
METHODS: The study was conducted in public housing units in the city of Belem, Northern Brazil, in 2003. Twelve houses were randomly chosen, three in each of the four established areas. Pyrethroids cypermethrin wettable powder, deltamethrin suspension concentrate, lambda-cyhalothrin wettable powder, and etofenprox wettable powder, were sprayed on the indoor wall surface of local houses. Their effects on the mortality of Anopheles were assessed from July to November. Wall bioassay was performed using plastic cones attached to insecticide and wild mosquitoes from the town of Peixe Boi.
RESULTS: Mortality rate varied according to the type of wall that received the insecticide. Those insecticides applied to wood and non-plastered brick surfaces were more stable and lasted longer. Lambda-cyhalothrin presented shorter effect than the other insecticides, and etofenprox had residual effects up to four months and was more effective in non-plastered brick surfaces. There was no statistical difference between the effect of deltamethrin and cypermethrin in all surfaces tested, and the duration of the residual effect was satisfactory up to three months after spraying.
CONCLUSIONS: Deltamethrin and etofenprox presented greater performance when compared to the others. For these insecticides and formulations, a three-month interval between successive applications can be considered safe. In communities with predominance of houses with plastered brick surfaces, the smaller effectiveness of formulations should be considered, together with the importance of residual spraying as a vector control method in the area.