Divergent responses to urbanisation and forest cover shape the spatial distribution of Culex pipiens ecotypes in western Switzerland

BACKGROUND: Arthropod-borne viruses are increasingly reported across Europe, with Culex pipiens serving as the main vector of West Nile and Usutu viruses. The C. pipiens complex comprises two ecologically distinct ecotypes, pipiens and molestus, which can hybridise. These ecotypes are thought to differ in habitat preference, with C. p. molestus more frequent in urban environments and C. p. pipiens in natural ones. However, many studies have either not distinguished between these ecotypes or have investigated them without considering a clear landscape gradient. This information is nevertheless important for understanding vector distribution and the potential implications for virus transmission pathways and spillover risk. METHODS: A season-long survey was conducted from May to September 2025 across 57 sampling sites in Switzerland. Mosquitoes were morphologically identified, and C. pipiens ecotypes were distinguished using molecular analyses. We characterised landscape composition and their scale of effects, as well as meteorological conditions on the sampling dates to determine their influence on the presence and relative proportion of each C. pipiens ecotype. RESULTS: Agricultural landscapes promoted all ecotypes, urbanisation positively influenced C. p. pipiens but not C. p. molestus, and forest cover reduced the presence and relative proportion of hybrids. In addition, temperature was positively correlated with all ecotype presence, whereas rainfall had no detectable effect. CONCLUSIONS: The responses to landscape variables differ among C. pipiens ecotypes and across different landscape features. This highlights the complex, context-dependent interactions between the ecology of mosquitoes and the composition of their habitat, which ultimately determine their spatial distribution patterns.