Abstracts

Principal Investigator: William Reisen

This research tests the overarching hypothesis that temperature determines the duration of the extrinsic incubation period (EIP) and therefore the rate of West Nile virus (WNV) amplification during late winter and spring. This study expands upon the current degree-day temperature model by examining the effect of cycling temperatures and more recent WNV strains. The research will address the following objectives: 1) compare the duration of EIP for specific strains of WNV (NY99, WN02, and Kern200-11) at two constant temperatures, 2) if viral isolates differ, estimate duration of EIP at 5 constant temperatures for the Kern2000-11 isolate to revise the EIP model, 3) determine if EIP estimates differ based on constant versus daily cycling temperatures of the California spring. The results will be crucial for creating accurate temperature-related risk estimates in WNV response plans. In addition, the results could yield understanding of how WNV could be transmitted during late winter and spring when average temperatures remain below the previously estimated replication threshold. 

Principal Investigator: Peter Piermarini 

Mosquitoes are rapidly developing resistance to conventional insecticides that target the central nervous system. This research aims to disrupt the function of the protein hypothesized to be key in the role of absorption of blood plasma by the adult female mosquito. It seeks to evaluate an inward-rectifying potassium (Kir) channel (Kir2A) as a new potential molecular target for development of adult insecticides. This would likely lead to decreased reproductive value and/or death. The research could validate a new molecular target for mosquito control and provide insights into the physiology of the mosquito midgut.

Principal Investigator: Kenneth Linthicum

Contemporary mosquito control employs various chemicals. This project intends to determine an ideal combination of sucrose (honey, molasses, or sugar) to serve as a mosquito trap in regions of the world that lack access to dry ice or carbon dioxide canisters. The researchers will assess the synergistic effect of aromatic volatiles and metabolites produced by yeast fermentation of honey, molasses, and sugar on outdoor trapping of wild and laboratory mosquitoes.

Principal Investigator: Scott Bernhardt 

Mosquitoes are critical vectors of disease and management programs devote massive amounts of resources to reduce their populations. The frequent use of methoprene, a highly specific larvicide, places mosquito populations at risk of developing resistance. This study seeks to understand how the methoprene-tolerance gene (Met), suspected of conferring methoprene resistance, affects susceptibility in two US West Nile virus vectors (Culex tarsalis and Culex pipens).

Principal Investigator: Emma Weeks

Mosquito larvicides are an effective means of source reduction, controlling the population size so that the number of adult females that are present to bite and potentially spread pathogenic organisms is decreased. Currently utilized mosquito larvicides include insect growth regulators, organophosphates, oils and microbial agents.As resistance has developed to the  organophosphate, e.g. temephos, and microbial, e.g. Bacillus thuringiensis israelensis (BTi), larvicides that are commonly used alternativesare urgently needed. Amino acids, including essential amino acids such as L-methionine, have been shown to work as effective larvicides. Our study aims to evaluate the toxicity of methionine as a mosquito larvicide alone and in combination with existing larval control techniques by studying the effect of the chemical in several pestiferous mosquito genera, evaluating efficacy in combination with BTi and checking for non-target effects in other organisms that may be exposed to the treatment. Our study and potential 'product' will benefit mosquito and vector control districts and the public nationally and internationally by providing them with a new environmentally sustainable tool that they can use for control of pestiferous mosquitoes.

Principal Investigator: William Walton

The objectives of this project are to develop an integrated vector management (IVM) strategy (1) to reduce the use of adulticides against mosquitoes of public health importance, (2) to reduce mosquito harborage, and (3) to reduce the need for costly vegetation management in man-made wetlands used to improve water quality . We propose to study mosquito production, the co-occurring aquatic invertebrate community including mosquito predators, the temporal changes in the emergent vegetation and nutrient removal capabilities in six replicate 0.1-ha wetlands planted with the alkali bulrush, Schoenoplectus maritimus . The alkali bulrush is smaller than the macrophytes found typically in constructed wetlands and has characteristics that may reduce mosquito production and the need for costly vegetation management.  During the winter between years 1 and 2, the wetlands will be divided into two hydrological regimes that are predicted to differ in the potential to reduce the biomass of the natural winter dieback of S. maritimus and result in significantly smaller mosquito populations during the period when arboviruses increase naturally in the reservoir and vector populations . The effects of the two hydrological regimes on the sustainability of the emergent plants, water quality performance, and reduction of mosquito populations will be assessed in year 2.

Principal Investigator: Chrisopher M. Barker 

The container-breeding mosquito, Aedes albopictus, has been discovered in Los Angeles County during the summer of 2011 after remaining undetected for nearly a decade. Preliminary analyses indicate that recently collected specimens are closely related to others collected in 2001-2002 near Port of Los Angeles, raising the possibility that a local population has become established following the earlier introduction. We propose using biologically realistic mathematical models for Ae. albopictus dispersal in combination with data from local mosquito control agencies to estimate the rate of spread for this species and the likely timing of past introduction(s) based on the current distribution pattern. Using the model, we will compare larval and adult control methods to determine which would be most effective for containment and eradication. The results would be important for informing control of Ae. albopictus and potential future invasions of container-breeding mosquitoes.

Principal Investigator: Bradley White

West Nile Virus (WNV) remains a major health concern for Californians. Indeed, after several years of stasis the number of human cases in the state more than doubled from 2011 to 2012. In California, Culex mosquitoes are the primary vectors of the WNV. However, there is a substantial variation in the ability of different populations of Culex to transmit the disease. We will use cutting-edge generic tools to comprehensively identify the distinct popuplations of Culex vectors across the state. This information will enable studies to determine which mosquito populations pose the greatest risk to public health, allowing for more specific targeting of insecticides and trapping. Ultimately, our research should improve the public health of Californians by enhancing the efficiency of mosquito control. 

Principal Investigator: William Reisen

The current degree-day temperature model describing the impact of temperature on the duration of the extrinsic incubation period [EIP] of West Nile virus (WNV) in Culex tarsalis was estimated using the NY99 strain of virus and has not been validated using cycling temperatures or more recent viral strains. The proposed research tests our overarching hypothesis that temperature determines the duration of the EIP and therefore the rate of WNV amplification during late winter and spring by addressing three specific objectives: 1) compare the duration of the EIP for NY99, WN02 and a contemporary California WNV isolate at two constant temperatures, 2) if the viral isolates differ, revise the EIP model by estimating the duration of the EIP at 5 constant temperatures for the new WNV isolate, and 3) determine whether daily cycling temperature differs from constant temperature using vernal temperatures measured in California. This work is critical for assuring accurate temperature-related risk estimates in WNV response plans and the CalSurv Gateway, and for understanding how WNV may be transmitted during late winter and spring when most average temperatures remain below the replication threshold estimated from our previous study.

Principal Investigator: William Walton, UC Riverside

Summary: This research addresses important aspects of disease surveillance for new and re-emerging diseases, topics listed among the MRF research needs. We feel that early recognition of new problems and baseline data determining their potential for being established in California through vector competence studies promotes public health by informing mosquito control agencies of potential risks. The geographic scope of this project is statewide and therefore there was no attempt to obtain letters of collaboration from individual districts. Back stopping in virus identification and assay development is provided by Dr AC Brault, Virologist in Division of Vector-borne Infectious Diseases, CDC, Ft Collins.

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