Mesocyclops brevisetosus Dussart and Sarnita, an indigenous copepod in Indonesia, was evaluated as a potentially useful biological control agent against larval Aedes (Stegomyia). In the laboratory, female M. brevisetosus were found to readily consume mosquito larvae of species from 3 genera (Aedes aegypti, Culex quinquefaciatus, and Anopheles farauti). Mesocyclops brevisetosus preferentially fed on larvae of Ae. aegypti (mean 95% consumed), followed by Cx. quinquefasciatus (71%) and An. farauti (54%) during a 24-h period. An individual copepod consumed up to 43 1st and 2nd instars of Ae. aegypti within a 24-h period. In the field, a density of 25 adult copepods/400 ml of water in an artificial container prevented the establishment of Aedes mosquitoes by 98% compared to the control container (without copepods). A density of 50 copepods/400 ml of water completely prevented infestation with Aedes. Over a 12-wk period, evaluation of M. brevisetosus-treated ovitraps reduced Ae. aegypti by 38-100% compared to ovitraps without copepods. The introduced gravid copepods increased 2.5-6.7 times over the original cohort. Mesocyclops brevisetosus showed high fecundity in culture, with a mean of 58 nauplii produced per individual gestation cycle.