RNA interference (RNAi) is a conserved sequence-specific, gene-silencing mechanism that is induced by double-stranded RNA (dsRNA). One of the functions of this pathway is the defense against parasitic nucleic acids: transposons and viruses. Previous results demonstrated that viral infections in Drosophila melanogaster are fought by an antiviral RNAi response and that components of the endocytic pathway are required for dsRNA entry to initiate the RNAi response. Recently we have shown that infected insect cells spread a systemic silencing signal that elicits a protective RNAi-dependent immunity throughout the organism. This suggests that the cell-autonomous RNAi response is insufficient to control a viral infection and that flies also rely on systemic immune response to fight against such infections. As a junior group leader, I will study the mechanisms that mediate the RNAi-based antiviral response in insects. By combining biochemical, cellular, molecular and genomic approaches, both in vivo and in cell culture, I will analyze the mechanisms underlying viral tropism, systemic propagation of the antiviral signal and the basis of the persistence of the antiviral state. Furthermore, I will examine whether the dsRNA-uptake pathway is conserved in mosquitoes and its relationship with viral immunity in that host. This comprehensive approach will tackle how this nucleic acid-based immunity works in insects to generate an anti-viral stage. A better understanding of the role of RNA silencing in insects during virus infection will allow the exploitation of this pathway for improvement of public health related problems such as arbovirus infection and disease.