Scented Sugar Baits Enhance Detection of St. Louis Encephalitis and West Nile Viruses in Mosquitoes in Suburban California.

Scented sugar baits deployed in California deserts detected early West Nile virus (WNV) transmission by mosquitoes, representing a potential improvement to conventional arbovirus surveillance that relies heavily on infection rates in mosquito pools. In this study, we expanded deployment of scented sugar baits into suburban Sacramento and Yolo (2015, 2016) and Riverside Counties (2016), California. The goal of the study was to determine whether scented sugar baits detect WNV and St.

Environmentally Dependent Density-Distance Relationship of Dispersing Culex tarsalis in a Southern California Desert Region.

The direct inclusion of environmental factors into the empirical model that describes a density-distance relationship (DDR) is demonstrated on dispersal data obtained in a capture-mark-release-recapture experiment (CMRR) with Culex tarsalis conducted around the community of Mecca, CA. Empirical parameters of standard (environmentally independent) DDR were expressed as linear functions of environmental variables: relative orientation (azimuthal deviation of north) of release point (relative to recapture point) and proportions of habitat types surrounding each recapture point. The yielded regression model (R(2)  =  0.

Host selection patterns of Culex tarsalis (Diptera: Culicidae) at wetlands near the Salton Sea, Coachella Valley, California, 1998-2002.

The bloodmeal hosts used by Culex tarsalis Coquillett collected along the Salton Sea in Coachella Valley, CA, during 1998-2002 were identified using sequences of the cytochrome c oxidase I gene identified from Barcode of Life database. Overall, 265 (83.3%) of 318 bloodmeals were identified, of which 76.

Use of scented sugar bait stations to track mosquito-borne arbovirus transmission in California.

Laboratory and field research was conducted to determine if Culex tarsalis Coquillett expectorated West Nile virus (WNV) during sugar feeding and if a lure or bait station could be developed to exploit this behavior for WNV surveillance. Experimentally infected Cx. tarsalis repeatedly expectorated WNV onto filter paper strips and into vials with wicks containing sucrose that was readily detectable by a quantitative reverse transcriptase-polymerase chain reaction assay.

Residual mosquito barrier treatments on U.S. military camouflage netting in a southern California desert environment.

Treating perimeters of vegetation with residual insecticides for protection from mosquito vectors has potential for U.S. military force health protection.

Evaluation of ULV and thermal fog mosquito control applications in temperate and desert environments.

Ultra-low-volume (ULV) and thermal fog aerosol dispersals of pesticides have been used against mosquitoes and other insects for half a century. Although each spray technology has advantages and disadvantages, only 7 studies have been identified that directly compare their performance in the field. US military personnel currently operating in hot-arid environments are impacted by perpetual nuisance and disease vector insect problems, despite adulticide operations using modern pesticide-delivery equipment such as ULV.

Effects of warm winter temperature on the abundance and gonotrophic activity of Culex (Diptera: Culicidae) in California.

Culex tarsalis Coquillett, Cx. quinquefasciatus Say, and Cx. pipiens L.

Evaluation of barrier treatments on native vegetation in a southern California desert habitat.

Treating perimeters with residual insecticides for protection from mosquito vectors has shown promise. These barrier treatments are typically evaluated in temperate or tropical areas using abundant vegetation as a substrate. However, there is an emerging interest to develop this technology to protect deployed US troops in extreme desert environments with sparse vegetation.

Persistent West Nile virus transmission and the apparent displacement St. Louis encephalitis virus in southeastern California, 2003-2006.

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) invaded the Colorado Desert biome of southern California during summer 2003 and seemed to displace previously endemic St. Louis encephalitis virus (family Flaviviridae, genus Flavivirus, SLEV, an antigenically similar Flavivirus in the Japanese encephalitis virus serocomplex). Western equine encephalomyelitis virus (family Togaviridae, genus Alphavirus, WEEV), an antigenically distinct Alphavirus, was detected during 2005 and 2006, indicating that conditions were suitable for encephalitis virus introduction and detection.

Intensive early season adulticide applications decrease arbovirus transmission throughout the Coachella Valley, Riverside County, California.

In the Coachella Valley of California the seasonal onset of St. Louis encephalitis virus (SLEV), western equine encephalomyelitis virus (WEEV), and West Nile virus (WNV) has been detected consistently at the shoreline of the Salton Sea near the community of North Shore. The timing and intensity of initial amplification in the Culex tarsalis Coquillett/wild bird cycle at this focus seemed closely linked to the subsequent dispersal of virus to the rest of the Coachella Valley and perhaps southern California.

Evaluation of pyrethrin aerial ultra-low volume applications for adult Culex tarsalis control in the desert environments of the Coachella Valley, Riverside County, California.

Eliminating infected female mosquitoes by aerial applications of ultra-low volume adulticides is the intervention strategy currently recommended to interrupt the epidemic transmission of encephalitis viruses, including West Nile. The current research optimized pyrethrin formulations and evaluated their efficacy in the desert environment of the Coachella Valley, Riverside County, California. After seven trials during 2004, a 1:2 by volume mixture of Pyrenone 25-5 in BVA oil optimized particle size, droplet descent to ground level, and kill of sentinel mosquitoes.

Evaluation of pyrethrin and permethrin ground ultra-low volume applications for adult Culex control in rural and urban environments of the Coachella Valley of California.

Six experimental ground ultra-low volume (ULV) applications of Pyrenone 25-5 (0.0025 lb/acre) and Aqua-Reslin (0.007 lb/acre) were made by truck-mounted Pro-Mist or London Fog equipment over 1-mi2 study areas in rural and residential environments of the Coachella Valley, Riverside County, California.

Role of corvids in epidemiology of west Nile virus in southern California.

The invasion of different southern California landscapes by West Nile virus (WNV) and its subsequent amplification to epidemic levels during 2004 enabled us to study the impact of differing corvid populations in three biomes: the hot Colorado desert with few corvids (Coachella Valley), the southern San Joaquin Valley (Kern County) with large western scrub-jay but small American crow populations, and the cool maritime coast (Los Angeles) with a large clustered American crow population. Similar surveillance programs in all three areas monitored infection rates in mosquitoes, seroconversion rates in sentinel chickens, seroprevalence in wild birds, numbers of dead birds reported by the public, and the occurrence of human cases. Infection rates in Culex tarsalis Coquillett and sentinel chicken seroconversion rates were statistically similar among all three areas, indicating that highly competent mosquito hosts were capable of maintaining enzootic WNV transmission among less competent and widely distributed avian hosts, most likely house sparrows and house finches.

Overwintering of West Nile virus in Southern California.

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) invaded southern California during 2003, successfully overwintered, amplified to epidemic levels, and then dispersed to every county in the state. Although surveillance programs successfully tracked and measured these events, mechanisms that allowed the efficient overwintering and subsequent amplification of WNV have not been elucidated. Our current research provided evidence for three mechanisms whereby WNV may have persisted in southern California during the winters of 2003-2004 and 2004-2005: 1) continued enzootic transmission, 2) vertical transmission by Culex mosquitoes, and 3) chronic infection in birds.

West Nile virus in California.

West Nile virus (WNV) was first isolated in California during July 2003 from a pool of Culex tarsalis collected near El Centro, Imperial County. WNV transmission then increased and spread in Imperial and Coachella Valleys, where it was tracked by isolation from pools of Cx. tarsalis, seroconversions in sentinel chickens, and seroprevalence in free-ranging birds.

Factors influencing the outcome of mark-release-recapture studies with Culex tarsalis (Diptera: Culicidae).

Three potentially important aspects of mark-release-recapture experimentation were addressed: 1) source of mosquitoes for release, 2) time of release, and 3) weather during recapture. Culex tarsalis Coquillett mosquitoes collected as adult host-seeking females from dry ice-baited traps (CO2 traps) operated within the study area (local) were recaptured more frequently than females collected from traps operated outside the study area (foreign) or reared from field-collected immatures (reared). These results supported published studies on Anopheles and Ochlerotatus that indicated mosquitoes may "memorize" flight paths within their environment.

Nocturnal microhabitat distribution of adult Culex tarsalis (Diptera: Culicidae) impacts control effectiveness.

Suction traps (30 cm diameter) were more effective for non-attractant sampling of flying adult Culex tarsalis Coquillett than were smaller CDC (5.5 cm diameter), Malaise or ramp traps. Comparative catch in suction traps operated in a variety of vegetation types indicated that females congregated along elevated ecotones and were significantly less abundant flying over low vegetation or under and over elevated vegetation.