Spinosad 12% suspension concentrate (SC) and 0.5% granular (G) formulations were tested against Culex quinquefasciatus immatures at 3 dosages—50, 100, and 150 mg active ingredient (AI)/m²—in cesspits, street drains, and disused wells in comparison with temephos 1% G at 1 part per million. The 2 formulations reduced the density of pupae of Cx. quinquefasciatus by 80–100% for 7–14 days in cesspits, 7–18 days in drains, and 33–69 days in disused wells at the 3 dosages tested. The 12% SC and 0.5% G formulations were equally effective in suppressing the larval and pupal populations of Cx. quinquefasciatus in all the habitats treated. At 100 mg AI/m² in drains and cesspits, the efficacy of spinosad 0.5% G was greater than that of temephos (1% G) and that of spinosad 12% SC was comparable to that of temephos (1% G) applied to the 2 habitats. In disused wells, both the formulations lasted longer than temephos. Based on the small-scale trial, the rate of 150 mg AI/m² of spinosad was selected for field application to cesspits and drains and 50 mg AI/m² for application to disused wells. The efficacy observed in medium-scale trials was in agreement with that of small-scale trials. The trial showed that the 2 formulations of spinosad can be used for larval control of Cx. quinquefasciatus, at 50 mg AI/m², applied at weekly intervals to cesspits and street drains and at monthly intervals to disused wells. At the higher dose of 150 mg AI/m², the 2 formulations were effective in suppressing the pupal population for 2 wk in cesspits and street drains and for 2 months in disused wells.