ModelingCulex tarsalisAbundance on the Northern Colorado Front Range Using a Landscape-Level Approach

Abstract

Remote sensing and Geographic Information System (GIS) data can be used to identify larval mosquito habitats and predict species distribution and abundance across a landscape. An understanding of the landscape features that impact abundance and dispersal can then be applied operationally in mosquito control efforts to reduce the transmission of mosquito-borne pathogens. In an effort to better understand the effects of landscape heterogeneity on the abundance of the West Nile virus (WNV) vector Culex tarsalis, we determined associations between GIS-based environmental data at multiple spatial extents and monthly abundance of adult Cx. tarsalis in Larimer County and Weld County, CO. Mosquito data were collected from Centers for Disease Control and Prevention miniature light traps operated as part of local WNV surveillance efforts. Multiple regression models were developed for prediction of monthly Cx. tarsalis abundance for June, July, and August using 4 years of data collected over 2007-10. The models explained monthly adult mosquito abundance with accuracies ranging from 51-61% in Fort Collins and 57-88% in Loveland-Johnstown. Models derived using landscape-level predictors indicated that adult Cx. tarsalis abundance is negatively correlated with elevation. In this case, low-elevation areas likely more abundantly include habitats for Cx. tarsalis. Model output indicated that the perimeter of larval sites is a significant predictor of Cx. tarsalis abundance at a spatial extent of 500 m in Loveland-Johnstown in all months examined. The contribution of irrigated crops at a spatial extent of 500 m improved model fit in August in both Fort Collins and Loveland-Johnstown. These results emphasize the significance of irrigation and the manual control of water across the landscape to provide viable larval habitats for Cx. tarsalis in the study area. Results from multiple regression models can be applied operationally to identify areas of larval Cx. tarsalis production (irrigated crops lands and standing water) and assign priority in larval treatments to areas with a high density of larval sites at relevant spatial extents around urban locations.

Temporal and Spatial Variability of Entomological Risk Indices for West Nile Virus Infection in Northern Colorado: 2006–2013

“…Eisen et al (2010) found a positive association between proximity to irrigated agriculture and elevated WNV incidence. Schurich et al (2014) demonstrated a negative correlation between elevation and Cx. tarsalis abundance within Fort Collins.…”

“…These include ecological variables such as temperature, precipitation, and land usage and cover (Ezenwa et al 2007, Brown et al 2008, Eisen et al 2010, Kilpatrick 2011). In addition, mosquito feeding preferences (LaDeau et al 2007, Farajollahi et al 2011), availability of larval and adult habitats (Schurich et al 2014), and local avian species diversity (Ezenwa et al 2006) can also influence WNV transmission. These factors and others likely contributed to the seasonal and spatial differences in VI we observed during the study period.…”

“…pipiens and Cx. tarsalis (Barker et al 2010, Schurich et al 2014), we hypothesized that the city is spatially and temporally heterogeneous for Culex female abundance, WNV infection rates, and subsequently VI. These dynamics would indicate the entomological risk for WNV infection may be higher in specific portions of the city compared with others.…”

Projection of Climate Change Influences on U.S. West Nile Virus Vectors

“…The WNV vectors studied here are limited both in their presences and in their seasonal activity by elevation (Barker et al 2010; Schurich et al 2014). While the analysis presented here did not allow us to specifically evaluate vector distribution across elevations, we can expect that, just as cooler northerly latitudes may become more permissible, higher elevations may also become more permissible and conversely some of the lower elevations may become less permissible.…”

Risk factors for West Nile virus infection and disease in populations and individuals

“…In northern Colorado, where Cx. tarsalis is also primary, irrigation and manual control of water on the landscape was also found to promote mosquito abundance (36). In addition to being in areas with high vector abundance, risk for becoming infected can be influenced by time spent outdoors and decisions on whether to adopt personal precautions against mosquito bites.…”