A biological method was used to synthesize stable silver nanoparticles that were tested as mosquito larvicides against Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus. Annona squamosa leaf broth (5%) reduced aqueous 1 mM AgNO₃ to stable silver nanoparticles with an average size of 450 nm. The structure and percentage of synthesized nanoparticles was characterized by using ultraviolet spectrophotometry, X-Ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy methods. The median lethal concentrations (LC₅₀) of silver nanoparticles that killed fourth instars of Ae. aegypti, Cx. quinquefasciatus, and An. stephensi were 0.30, 0.41, and 2.12 ppm, respectively. Adult longevity (days) in male and female mosquitoes exposed as larvae to 0.1 ppm silver nanoparticles was reduced by ~30% (p<0.05), whereas the number of eggs laid by females exposed as larvae to 0.1 ppm silver nanoparticles decreased by 36% (p<0.05).