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A field study was carried out on the year-long residual activity of the insect growth regulator (IGR) pyriproxyfen (Nylar 0.5G) in comparison with methoprene (Altosid® XRP Pellets) against mosquito developmental stages in catch basins in northwestern Riverside County, southern California. Pyriproxyfen was applied at 75, 100, 125, 150, 175 g per catch basin and methoprene at 3.5 g per catch basin. A total of 80 catch basins (10 per each treatment and 20 for control) were used. Posttreatment observations of catch basins were carried out at weekly intervals, with all pupal collections reared to adults. Mosquito species composition in this study, consisting mostly of Culex species (693), was predominated by Cx. quinquefasciatus (92.8%), followed by Cx. erythrothorax (5.5%), Cx. tarsalis (1.2%), Cx. stigmatosoma (0.3%), and Cx. thriambus (0.2%). Activity of both IGRs was expressed as percent inhibition of adult emergence (% IAE). Data generated on % IAE showed that, like methoprene, pyriproxyfen provided complete control of mosquitoes at 75, 125, and 175 g per catch basin up to 50 wk posttreatment at the Riverside amusement park, whereas its activity against mosquitoes in catch basins treated with 100 g and 150 g at the Eastvale site was short-lived, up to 48 wk. Water samples, bioassayed against laboratory-reared, 4th-stage larvae of Cx. quinquefasciatus 1-2 wk after the 50-wk-long study, showed evidence of significant % IAE (∼50) by pyriproxyfen at the 2 higher rates (125 g, 175 g) used at the amusement park. In conclusion, pyriproxyfen can be used to effectively control mosquitoes in catch basins for 48-50 wk, depending on the rate of application., (Copyright © 2020 by The American Mosquito Control Association, Inc.)

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.