The objective of this study was to evaluate the efficacy and residual activity of Pyriproxifen on third-stage Aedes aegypti larvae and to determine susceptibility to this larvicide in Mazan and Nauta strains, along with their Rockefeller control strains. Tests were conducted in the laboratory at a concentration of 0.01 ppm. Efficacy was assessed by inhibition of emergence (EI) at 24 hours and residual activity for 90 days by monthly exposure of new larvae without renewing the solution. Susceptibility was determined based on the EI percentage, with strains with 98–100% EI considered susceptible. The results demonstrated 100% EI efficacy at 24 hours in all three strains (Mazan, Nauta, and Rockefeller). With 100% residual EI activity up to 30 days, decreasing to 89% in Mazan and 86.2% in Nauta at 60 days, and reducing to 19.3% and 52%, respectively, at 90 days. The three strains tested we...