West Nile virus (WNV) is circulating locally in Southern and Eastern Europe, and over the last decade it has spread to new areas, e.g. north-eastern Italy. With this project, we suggest to assess the diversity, seasonal abundances and host preferences of mosquitoes at places considered as putative ‘hot spots’ for WNV introduction/transmission in Switzerland (extended wetlands and suburban sites on either side of the Alpine crest) and to experimentally determine the vector competence of Swiss mosquito populations for WNV under different realistic environmental conditions. This work will provide basic data on the vector capacity of the various mosquito species identified as putative vectors for WNV and will essentially contribute towards devising a risk assessment of WNV transmission in Switzerland.