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Supplementary Matyerials for the Journal of the European Mosquito Control Association: Epic 2023 rainfall causes mosquito population explosions and impacts West Nile virus surveillance in Colorado, USA

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posted on 2024-10-22, 12:39 authored by A. Wanek, K. Renfro, M.J. Weissmann, R.G. Hancock

The front range of Colorado, USA, has a population of nearly five million people spread out over a mosaic of urban/suburban build-up and intensive irrigation-based agriculture. The temperate climate and harsh winters produce a 15-week summer ‘mosquito season’ during which time mosquito surveillance and control is practiced. Aedes vexans (Meigen, 1830) and Culex tarsalis Coquillett, 1830, are the most abundant species here, Cx. tarsalis being the main vector of endemic West Nile virus (WNV) transmission. Our purpose was to assess the impacts of record drought-busting precipitation on large-scale mosquito surveillance conducted by seasonal employees from regional University science programmes. Seasonal mosquito surveillance staff for Vector Disease Control International (VDCI, a Rentokil Company) were specifically recruited from the Biology Department at Metropolitan State University of Denver (MSUD). Surveillance technicians set CO2-baited CDC miniature light traps, retrieved them the next day and returned to the lab for sorting and pooling of Cx. tarsalis into groups of 65 which were then tested for WNV. We selected traps within each of three focus zones: five urban traps in Denver county, and 15 traps in each of two heavily irrigated agricultural areas (Boulder and Weld counties) and compared monthly rainfall and mosquito abundance from 2020-2022, typical years, and 2023, the record-breaking year. Cumulative rainfall in each county from May through mid-September in 2020, 2021 and 2022 did not exceed 21.5 cm while totals during 2023 exceeded 37 cm. In all counties, the median numbers of mosquitoes per trap in 2023 were dramatically higher than in 2020-2022 and this increased both worker hours and the necessity of catch estimations (instead of complete trap counts). Through all, the staff were proud and maintained high morale. By specifically recruiting undergraduate students of the biological sciences branch, we filled seasonal staff positions with talented, flexible and driven employees who viewed their jobs as a career step.

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