The high toxicity and physical properties of DDT make it very adaptable for use as a mosquito larvicide. It was tested in the laboratory using various methods of application and at different dosages, against larvae of Anopheles quadrimaculatus. The weathering . of surface applications was detd. by subjecting the tests to repeated artificial rains. DDT was toxic as a dust to 62% of the larvae when applied at the rate of 0.0001 lb. per acre. As a suspension at 0.01 ppm. DDT gave practically 100% mortality in 48 hrs., being > 100 times as toxic as phenothiazine. DDT is adaptable to surface applications in dusts and in oils, and to use in emulsions and suspensions. It is resistant to wetting and can be used in dusts prepd. from solid solns. in various diluents. In stable emulsions and suspensions at 0.1 ppm. it remains effective for a long time.