The residual efficacy of pyriproxyfen against Aedes aegypti (L.) was examined by treating 2-liter buckets with a range of rates of Sumilarv 0.5G (1 00, 10, 1, and 04 mg product/liter or nominal dose of 500, 50, 5, and 0.5 ppb active ingredient) under semifield conditions. Approximately every 2 wk, pupal emergence inhibition (EI) was measured by using Cairns colony Ae. aegypti. Pooled water samples from the five replicate buckets were analyzed for active pyriproxyfen by using ultra-high-pressure liquid chromatography with tandem mass spectrometry detection. A strong dose—response in EI was exhibited, with the 0.1 mg/liter giving ≈50% EI for only the initial week, whereas the 10 and 100 mg/liter doses produced EI > 90% for 8 and 40 wk, respectively. Measurable levels of active ingredient were detected in the 100, 10, and 1 mg/liter treatments, with measured starting concentrations of just 1-2-1.4% of the delivered (active ingredient) dose. Pyriproxyfen was detected in the 100 mg/liter treatment through the entire course of the trial (60 wk).