Backpack sprayer applications of permethrin, d-phenothrin, and resmethrin to vegetation and plants at Anastasia Island, St. Augustine, FL, were evaluated for duration of residual efficacy against adult mosquitoes. All treatments produced 100% mortality (24 h) of mosquitoes in test cages placed within the vegetation. At 48 h and 1 wk posttreatment, insecticide treatments resulted in 70–100% reduction of adult mosquitoes caught by Centers for Disease Control and Prevention traps baited with 1-octen-3-ol. Insecticide residues in excised leaves from both treated and control areas of the study sites were evaluated against adult female Culex quinquefasciatus by laboratory bioassay. Permethrin produced 90% mortality up to 1 wk postapplication. Both d-phenothrin and resmethrin produced nearly this level of mortality for a much shorter duration of <48 h postapplication, with residual effects dropping significantly thereafter. Average insecticide concentrations in leaves were quantified by gas chromatography/mass spectroscopy, and some correlation was observed between chemical and biological results.