The mosquito C. p. pipiens L. never colonize sewerage water covered with duck weed. The Lemna minor vegetations affected the identification of the oviposition site by the females. The amputation of sensilla made the mosquito incapable of choosing the oviposition site. The immature stages of the mosquito are susceptible to the water borne synomones of the duck weed; the first instar larvae are most susceptible and have high mortality.