Residual efficacy evaluation of the insecticides Deltamethrin WG and Etofenprox WP under different conditions and surfaces in a malaria-endemic area of the Eastern Amazon.

Indoor Residual Spraying is widely used as a method of malaria control. The objective of this study was to evaluate the residual effect of Deltamethrin WG and Etofenprox WP under three different conditions: 1) laboratory panels; 2) Semi-field and 3) directly in the field and to verify the susceptibility status of An. (Nys.) albitarsis s.l.. For Etofenprox WP, mortality rates observed in CW did not exceed 80%, except in the first 24 hours in Semi-field and Field conditions. In WW, mortality was above 80% throughout the six-month period in all three conditions evaluated. For Deltamethrin WG, the pattern varied according to substrate and condition: in CW, mortality was at or above 80% during the six months in the Panel condition, but fell below the limits in the second month in Semi-field and in the third month in Field conditions. In WW, mortality also remained above 80% for six months in the Panel condition, while in Semi-field it exceeded the limits only in the first month; in the Field condition, an oscillating pattern around 80% was observed, with recurring efficacy peaks in months two, four, and six. Susceptibility bioassays in An. (Nys.) albitarsis s.l. 100% knockdown was observed among female subjected to a 0.05% concentration of Deltamethrin, with a 24-hour mortality rate of 91.1 %, indicating possible resistance. At a concentration of 0.25 %, the 24-hour mortality rate was above 98 %, indicating low resistance intensity.