In this report, an RT-PCR approach based on the use of degenerate primers allowed the identification of negeviruses in four different species of mosquitoes (Ochlerotatus caspius, Culex pipiens, Cx. theileri and Cx. univittatus) collected in southern Portugal. The genomes of two of these viruses, sequenced to full completion, were shown to encode all the proteins encoded by previously described negeviruses. One of these viruses induces exuberant cytopathic effect in insect cell culture, with no obvious signs of apoptosis induction, replicating very rapidly and allowing for the detection of viral genomes in the infected culture supernatant as soon as 4h post-infection. This virus was also shown to use a dsRNA intermediate, which was found to be fully formed and active 3h after infection. Phylogenetic analysis of two products encoded by the viral ORF1 placed both viruses among Negev virus cluster, in the recently proposed Nelorpivirus taxon.