Arboviruses are serious pathogens for men but cause little damage to their arthropod vectors. We have studied how a mosquito cell line derived from one of the relevant vectors for arboviruses responds to Bunyamwera virus, a well-characterized arbovirus. Confocal, live cell microscopy and electron microscopy showed that Bunyamwera virus induces deep changes in mosquito cells. Early in infection these cells develop long projections and create new intercellular connections where cell organelles and viral proteins are detected. Live cell microscopy shows that these connections are developed before viral protein can be detected by immunofluorescence. Interestingly, their proliferation is accompanied by a progressive trapping of the nucleocapsid and RNA polymerase viral proteins into large cytoplasmic aggregates. A significant drop in the release of infectious virions then follows. Before that, numerous viruses assemble in peripheral Golgi stacks and they apparently exit the cells immediately since they do not accumulate intracellularly. This mechanism of assembly seems to cause little damage to the integrity of cell endomembranes. The characterization of the antiviral mechanisms operating in mosquito cells can be of great help in the fight against pathogenic arboviruses.