Impact of seasonal rainfall variation and larvicide application on weekly adult mosquito densities between April 2005 and June 2007. A. Rainfall and densities of adult Culex species, B. Rainfall and densities of adult Anopheles gambiae s.l., C. The ratio of densities of An. gambiae s.l. in intervention wards relative to non-intervention wards. The line representing the x-axis in panel C represents equivalence of densities in intervention and a priori selected non-intervention wards while the vertical black line represents the initiation of larviciding activities. The thick, broken horizontal line in panel C represents the ratio of exposure estimated to be provided by an insecticide-treated net in urban Dar es Salaam .