The Role of Climatic and Density Dependent Factors in Shaping Mosquito Population Dynamics: The Case of Culex pipiens in Northwestern Italy

Culex pipiens mosquito is a species widely spread across Europe and represents a compe- tent vector for many arboviruses such as West Nile virus (WNV), which has been recently circulating in many European countries, causing hundreds of human cases. In order to iden- tify the main determinants of the high heterogeneity in Cx. pipiens abundance observed in Piedmont region (Northwestern Italy) among different seasons, we developed a density- dependent stochastic model that takes explicitly into account the role played by tempera- ture, which affects both developmental and mortality rates of different life stages. The model was calibrated with a Markov chain Monte Carlo approach exploring the likelihood of recorded capture data gathered in the study area from 2000 to 2011; in this way, we disen- tangled the role played by different seasonal eco-climatic factors in shaping the vector abundance. Illustrative simulations have been performed to forecast likely changes if tem- perature or density–dependent inputs would change. Our analysis suggests that inter-sea- sonal differences in the mosquito dynamics are largely driven by different temporal patterns of temperature and seasonal-specific larval carrying capacities. Specifically, high tempera- tures during early spring hasten the onset of the breeding season and increase population abundance in that period, while, high temperatures during the summer can decrease popu- lation size by increasing adult mortality. Higher densities of adult mosquitoes are associated with higher larval carrying capacities, which are positively correlated with spring precipita- tions. Finally, an increase in larval carrying capacity is expected to proportionally increase adult mosquito abundance.