Environmental forcing and density-dependent controls of Culex pipiens abundance in a temperate climate (Northeastern Italy)

New and old mosquito-borne diseases have emerged and re-emerged in temperate regions over the recent past, but a mechanistic understanding of mosquito population dynamics, a fundamental step toward disease control, remains elusive. We propose here a Gompertz-based approach to address two obstacles to the development of vector dynamics models in temperate regions: (i) the inclusion of endogenous processes (e.g. density limitation, delayed responses, etc.) and the evaluation of their relative importance vs. exogenous environmental forcings; (ii) the inclusion of realistic descriptions of hydrologic processes and the evaluation of soil moisture as a more direct driver of mosquito population dynamics. The new model is based on a hierarchical state-space structure and is applied to the description of the abundance of Culex pipiens – a West Nile Virus vector – in the Po River Delta region (Northeastern Italy), using weekly mosquito abundance observations at more than 20 sites in the period May–September in 2010 and 2011. The hierarchical structure provides an efficient way of fully exploiting the information from a large network of observation sites. We find that Cx. pipiens abundance has significant density dependence at the one-week scale, which is coherent with its larval developmental time during the summer. This result points to the importance of endogenous population dynamics, most often neglected in mosquito population models, usually simply driven by exogenous environmental forcings. Among exogenous controls, temperature, daylight hours, and soil moisture were found to be most influential. Use of precipitation or soil moisture to force the model leads to very similar predictive skills. The negative correlation of soil moisture and mosquito population may be attributed to the abundance of water in the region (e.g. due to irrigation) and the preference for eutrophic habitats by Cx. pipiens. Variations among sites were highly correlated with land-use factors. The carrying capacity is seen to decrease with the distance to the nearest rice field, while the maximum population growth rate was positively related with the Normalized Difference Vegetation Index, a proxy of vegetation cover. The model shows a satisfactory performance in explaining the variation of mosquito abundance over a horizon of 1 week, particularly as far as peak timing and magnitude are concerned. Large rates of change of population abundance remain difficult to predict, as in other existing models, pointing to persisting gaps in our understanding of the mechanisms regulating mosquito population dynamics.