My PhD thesis at ISEM aims to better understand the mechanisms of co-infection of West Nile virus (WNV) and Usutu virus (USUV) in Culex pipiens mosquito, in the context of climate change. I explore the dynamics of replication and transmission of emerging WNV and USUV strains through in vitro (cell cultures) and in vivo (entomological experiments) models, simulating various climatic conditions to assess the influence of the environmental context on vector competence. My research combines molecular biology, transcriptomics, and proteomics, as well as experimentation in a secure insectarium, in order to anticipate the epidemiological evolution of these viruses in Europe. These works are carried out between ISEM, CIRAD in Montpellier and CIRAD in Guadeloupe.