The effect of organic enrichment of the larval habitat on mosquito oviposition was determined in 2 replicated field experiments. In the first study, Culex stigmatosoma and Culex quinque-fasciatus oviposition (as measured by the number of early instar larvae) reached a maximum peak soon after flooding and then declined to a substantially lower equilibrium level. A group of ponds that later received supplemental organic matter had a significant increase in oviposition soon after the additional organic matter was added. In the second experiment, a similar ovipositional pattern was noted by the sampling of egg rafts along transects and determining larval abundance by the dipping technique. In the second experiment a mixture of Culex stigmatosoma and Culex tarsalis larvae was collected.