piRNA pathway is not required for antiviral defense in Drosophila melanogaster

In animals, one of the main forms of RNA interference involves Piwi-interacting RNAs (piRNAs), which protect genomes against the activity of transposable elements. Several groups have recently described piRNAs from viruses in mosquitoes and suggested their involvement in antiviral defense. To understand the extent to which the piRNA pathway contributes to antiviral defense in insects, we used Drosophila melanogaster and different viruses. Using high-throughput sequencing, we were unable to find any evidence of piRNAs from viruses in flies. Furthermore, flies lacking components of the piRNA pathway were not unusually susceptible to viral infection. Taken together, our results indicate that fundamental differences have arisen between the antiviral defenses of flies and mosquitoes since they last shared a common ancestor >200 Mya.