Laboratory evaluation of the larvicidal efficacy of Ageratum conyzoides, Argemone mexicana and Azadirachta indica was carned out against Anopheles stephensi to develop an effective ecofriendly insecticide of plant origin. The methanol extract of A. indica was observed remarkably active with $LC_{50}$ values 18.2 and 13.1 ppm after 24 and 48 hours of exposure. Petroleum ether extracts of Ag. conyzoides with $LC_{50}$ 425.6 and 267.9 ppm, carbon tetra chloride extract of Ar. mexicana with $LC_{50}$ 313.2 and 240.3 ppm and petroleum ether extract of Az. indica with $LC_{50}$ 189.1 and 53. 5 ppm after 24 and 48 hours of exposure were also found effective. The impact of Az. indica methanol extract on the life cycle of malaria vector was further observed. Methanol extract of Az. indica causes deformities in different developmental stages of the malaria vector. Total developmental period was also extended from 10 to 15 It remarkably influenced hatching rates, larval-pupal transformation and development, adult emergence and growth index. Larval and pupal periods were also significantly prolonged.