Effect of effluent-treated water on mosquito development in simulated ponds at the Prado Wetlands of southern California.

Studies were conducted to determine the effect of water quality on mosquito development at the Prado Wetlands in southern California during 2003-04. In field experimental ponds, mosquito abundance was significantly higher in the sewage effluent-treated water than in untreated control. As compared to untreated control, treated water had higher dissolved oxygen, total nitrogen, phosphorus, and turbidity, and it showed lower electrical conductivity, sulfate, carbonates, and bicarbonates. Diverse vegetation and invertebrate fauna as influenced by water quality may have contributed to higher mosquito breeding in the treated ponds. In laboratory studies, the treated water did not significantly affect the developmental rate, adult emergence, sex ratio, and overall mortality of Culex quinquefasciatus and Culex tarsalis, known vectors of encephalitides in southern California. However, the ovipositional response, especially of the former species, was numerically higher to the treated than to untreated control water. Besides smaller body size of 3rd/4th instars of both species, 4th-stage larvae of Cx. quinquefasciatus reared in the treated pond water weighed lighter than the control larvae.