The efficacy of pyriproxyfen against the Australian salt-marsh mosquito, Aedes vigilax, was examined in 2 laboratory and 1 semi-field study using both technical grade and formulated products. In a dose-response study, the median emergence inhibition (EI50) and EI95 values were determined to be 0.019 and 0.076 ppb, respectively, for pyriproxyfen technical grade, 0.021 and 0.092 ppb for a microencapsulated formulation (Sumilarv 90CS), and 0.054 and 0.236 ppb for the formulated s-methoprene product, Altosid Liquid Larvicide. A further laboratory comparison of the microencapsulated formulation of pyriproxyfen and Altosid, at the nominal field rate for Altosid, showed that both products provided 100% emergence inhibition and this was confirmed in a semi-field study, which also included a granular formulation of pyriproxyfen (Sumilarv 0.5G).