Residual Activity of Pyriproxyfen Against Mosquitoes in Catch Basins in Northwestern Riverside County, Southern California.

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.

Field Evaluation of Pyriproxyfen Against Mosquitoes in Catch Basins in Southern California.

In a field trial, pyriproxyfen (Sumilarv 0.5% G) applied at 10 g and 50 g per catch basin and S-methoprene (Altosid XR briquet 2.1%) at 1 briquet per catch basin at a local park provided 100% inhibition of adult emergence (IAE) of the test species, Culex quinquefasciatus , for the first 3 wk. The IAE dropped to 69% to 85% for pyriproxyfen and 68% for methoprene at 4 wk posttreatment. The IAE at 5 to 8 wk posttreatment, although remaining high, was overshadowed by high mortality in control catch basins. The high mortality in control could be attributed to autodissemination of pyriproxyfen by mosquitoes from treated to untreated catch basins.

Population Dynamics of Blood-Fed Female Mosquitoes and Comparative Efficacy of Resting Boxes in Collecting them from the Northwestern Part of Riverside County, California.

OBJECTIVES: Testing of blood-fed mosquitoes plays an integral role in arbovirus surveillance and in understanding its interaction mechanisms between host, vector and reservoir. The present study was undertaken to evaluate the efficacy of two different traps (gravid and resting boxes) for collection of blood-fed mosquitoes in the northwestern part of Riverside County. MATERIALS AND METHODS: Three trapping sites were selected in the Northwest Mosquito and Vector Control District of Riverside County, California. At each site resting boxes and gravid traps were set; and mosquitoes were collected on a weekly basis between July-December 2009. Mosquitoes were transported over blue ice, identified up to species level on chill table, and classified as male, female and blood-fed females. RESULTS: During this study period, 3953 mosquitoes (826 blood-fed females) belonging to three different genera and eight species were collected; resting boxes collecting maximum number (seven) of mosquito species. Overall as well as individually in each trap kind, the most abundant mosquito species collected was Cx. quinquefasciatus. The proportion of blood-fed females of the Culex species collected in resting boxes was 28.8 times more, while of blood-fed females of Cx. quinquefasciatus was 32.2 times more than the proportion collected from gravid traps. CONCLUSIONS: Overall, the proportion of blood-fed female mosquitoes collected for each species trapped was highest in resting boxes. Additionally, resting boxes showed the advantage of extremely low running and maintenance cost; generation of no hazardous waste; quick turnaround time in terms of mosquito collection per man-hour spent; and they were less prone to vandalism or thefts.

Antigenic distribution of west nile virus in various organs of wildly infected american crows (corvus brachyrhynchos).

OBJECTIVE: Since its discovery in the western hemisphere in 1999, West Nile virus (WNv) has caused extensive bird mortality across North America, especially in American crows (Corvus brachyrhynchos) which are highly susceptible to WNv. In this study, antigenic distribution of WNv among different organs of American crows was studied, using the immunohistochemistry technique (IHC). MATERIALS AND METHODS: Dead crows reported by residents were collected, transported on ice, and were necropsied for heart, lung, brain, intestine, kidney, liver, spleen, pancreas, and gonad tissues. Gross examination was performed on brain, heart, lung, liver, kidney, spleen, bursa of fabricius, gastrointestinal tract, skeletal muscle, pancreas, reproductive tract, and skin. Gross hemorrhage of brain, splenomegaly, meningoencephalitis, myocarditis, and trauma were sporadically observed in some of the infected carcasses. Formalin-fixed paraffin-embedded tissue sections were stained with IHC technique followed by counter staining with hematoxylin and eosin. RESULTS: WNv antigen was detected in brain, spleen, heart, kidney, liver, gonads, intestine, lung, and pancreas. The spleen was found to be positive in all infected crows, followed by kidney, liver, and duodenum (95% each). Heart and pancreas were positive in 63% while brain was positive in 36.5% of the infected crows. CONCLUSION: More than one tissue sample is suggested to screen WNv infection using IHC technique. IHC has the advantage of correlating the visual destruction of tissue architecture with the presence of stained WNv antigen but as compared to PCR, IHC has the disadvantage of longer turnaround time, which is critical when used as a surveillance tool.

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.