SUMMARY The LC50 of Altosid against Culex univittatus eggs was 1.1276 ppm. The compound at 0.0137 ppin had no ovicidal activity. Exposure of Culex univittatus eggs for 2 days resulted in prolongation of larval and pupal period; 10.21-14.62% mortality in resulting pupae and reduced female ratio at higher concentrations. Exposure of first and second instar larvae of Culex univittatus to different concentrations resulted in larval mortality, but the effect on inhibition of adult emergence was not significant. The third and fourth instar larvae were the most sensitive whereas pupae were less sensitive to Altosid.