Aqueous suspensions of Culicinomyces conidia applied at rates of 5x109 and 1010 conidia/sq m in 1 m2 artificial ponds containing caged, laboratory reared mosquito larvae produced 100% mortality of Culex quinquefasciatus larvae and between 68-100% mortality of Anopheles annulipes larvae. In this test, there was no evidence of residual activity of the fungus in the test ponds beyond the first day after application against the Anopheles larvae and beyond the second day against the Culex larvae. A dosage rate of 1010 conidia/sq m applied in a 300 sq m pond containing natural populations of mosquito larvae produced 90-95% control of late instar Cx. australicus during the first week after application of the fungus but the population recovered during the second week. Larvae of An. annulipes, which were present in low density, were not controlled by the fungus in this trial.