An experimental release of preparasites of the mosquito nematode Romanomermis culicivorax Ross and Smith (= Reesimermis nielseni Tsai and Grundmann, auct., partim,) was made in 3 ponds via helicopter at the rate of ca. 4,629/m2 of water surface to control natural populations of Anopheles quadrimaculatus Say, An. crucians Wiedemann, and Culex erraticus (Dyar and Knab) larvae. Mean levels of parasitism of 52.4, 66.7 and 43.8% of the 1st instar Anopheles spp. and 39.2, 40.0 and 53.3% of 1st-4th instar larvae of Cs. erraticus from 3 ponds, respectively were obtained. The aerial spray tests indicated that a helicopter equipped with a simplex low profile spray system with TeeJet spray nozzles can be an effective means of disseminating the preparasitic stage of R. culicivorax in mosquito control operation.