Environmental and landscape factors associated with West Nile vector population dynamics in North-western Italy

The transmission risk of West Nile virus (WNV) is strongly related to the abundance of mosquito vectors. Culex spp. mosquitoes are considered the main enzootic vectors of WNV in Europe. We analysed an 11-year time series (from 2001 to 2011) of adult Culex pipiens mosquitoes, sampled in Piedmont region (North-western Italy), to determine the principal drivers of mosquito population dynamics. Linear mixed models were implemented to examine the relationship between Cx. pipiens population dynamics and environmental and landscape predictors. As environmental explanatory variables we used Land Surface Temperature, Normalized Difference Water Index (NDWI) and Precipitation (total amount and the number of days). In addition, we used some landscape variables that account for the proximity of mosquito traps to urban sites and rice fields. Cx. pipiens abundance is positively influenced by the number of days with precipitations during spring. Furthermore, several days of precipitations in spring postpones the onset of mosquito activity while lots of rainy days in summer extend the duration of Cx. pipiens activity. Higher temperatures during spring months anticipate the emergence of mosquitoes, while in warmer summer we observed longer Cx. pipiens breeding season but with overall lower total abundance of mosquitoes. Finally, higher values of NDWI in spring anticipate the emergence of mosquitoes and extend the Cx. pipiens breeding season