The efficacy of the insect growth regulator, pyriproxyfen, against Chironomus fusciceps was examined in the laboratory. A series of 6 concentrations (0.1-0.00001 ppm) was used. A positive relationship between mortality and concentration was observed in the pupal stage as well as in the larval stage. Pyriproxyfen caused 50 and 90% emergence inhibition of C. fusciceps at 0.00177 and 0.05369 ppm, respectively.