ABSTRACT
The present work investigates the optimum conditions for the application of the predaceous mosquito, Toxorhynchites splendens as a biological control agent for other vector mosquito species in Egypt such as, Culex pipiens, Anopheles pharoensis and Aedes caspius under field conditions. The predation efficiency of T. splendens larvae was found to increase as the temperature increased. At 30-35C the predaceous larvae consumed greater numbers of both C. pipiens and Ae. Caspius than that of A. pharoensis. The predation of T. splen -dens occurred almost similarly in all degree of salinity. On the other hand, light was found to have little effect on Toxorhynchites larvae where predation efficiency was decreased in the dark. The crowding had no effect on the predation. Also no mortality or natural diseases were observed among the tested insect larvae during the experim ental period, whereas the insect preferred to live in highly concentrated population. Toxorhynchites splendens larvae could live in turbid and distilled water. The maximum number of prey larvae consumed by all instars of T. splendens was at PH [8] followed by [7] and [9]. However, pH, below [6] and above 11 had a bad effect on the predaceous activity. The predation efficiency of T. splendens larvae increased gradually as the depth of water decreased .However captures of prey occurred either on the surface or at the bottom of the container