A simple technique was developed for the production of controlled-release systems (CRSs) for pyriproxyfen, an insect growth regulator active against the larvae of Culex pipiens, the most common species of mosquito found in developed countries. The CRSs consisted of a spongy core material encapsulated in a coating of a polyurethane or polyurea hydrogel, into which the active ingredient had been incorporated. The coating also included a surfactant to improve the low solubility in water of pyriproxyfen. The light core material enabled the CRS to float on the water surface, where the mosquitoe larvae are found. The type and amount of the polymeric coating and the amount of surfactant influenced the release profiles into water of the active ingredient. The release profiles of the CRSs were adjusted to the life cycle of the C. pipiens mosquito in order to obtain their optimal activity on the eighth day, which corresponds to the time of larval maturity.