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Official Statement Regarding Mosquito Control at the
Lower Duchesne River Wetlands Mitigation Project

December 4, 2008

Contrary to recent media reports¹, the Utah Reclamation Mitigation and Conservation Commission has not received any requests to conduct a baseline study of mosquito production at its Lower Duchesne River Wetlands Mitigation Project, located approximately 40 miles west of Vernal, Utah.

Furthermore, the Commission considers testing to establish a baseline population of adult mosquitoes infeasible; the wide area of dispersion of adult mosquitoes (up to 8-10 miles, and occasionally 25 miles) makes it impossible to determine where a particular mosquito may have hatched, or whether an individual site is or is not producing more adult mosquitoes at a given time. Establishing a baseline at a particular site would be highly problematic because mosquito production is also a function of local temperature, precipitation, and irrigation practices.

Monitoring to determine the presence of disease-carrying mosquitoes, especially Culex tarsalis, a mosquito capable of carrying West Nile Virus (WNV), is routinely conducted by mosquito abatement districts or local health departments in concert with the Utah Health Department. The data is available on the Internet at http://health.utah.gov/epi/diseases/wnv/.

A standard procedure for control of WNV infestations is to map potential mosquito breeding habitat, then have trained technicians conduct regular surveys in those areas to detect the presence of mosquito larvae capable of carrying the WNV. Technicians monitor mosquito producing habitat on a weekly basis by sampling for mosquito larvae which can usually be identified in the field. If culex tarsalis are found at a particular site, it is treated with the larvacide BTi. This larvacide is used because of its specificity to mosquito larvae. Continued monitoring typically reveals high rates of effectiveness, especially in less complex and more isolated areas.

Additionally, adult mosquitoes are monitored to determine the numbers of vector mosquitoes and their infection rates. The numbers and infection rates of adult vector mosquitoes help determine if additional control measure for adult mosquitoes are implemented.

As was described in the legally required environmental impact analysis documents, the Commission’s Record of Decision, and in a fact sheet published by the Commission (all of which are available on the Commission’s website at mitigationcommission.gov) the Commission has mapped all 2,082 acres of potential mosquito breeding habitat under baseline conditions within the 4,807-acre Project area (which includes approximately 421 acres that provide potential habitat for Culex tarsalis, as opposed to “nuisance mosquitoes” not known to carry WNV in Utah). Under an Operating Agreement with the Commission, the Ute Tribe will conduct treatment in the manner described above, as is done by Commission partners on other mitigation projects and by local, state and Federal entities on other potential mosquito breeding sites in Utah and throughout the United States.

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¹ “Feds Refuse Study To Track West Nile At Wetlands Project”, Reported by Rod Decker, 12/01/08 6:07 pm, www.kutv.com/content/news/local/story