Virus evolution in infected .

, a common vertically transmitted symbiont, can protect insects against viral infection and prevent mosquitoes from transmitting viral pathogens. For this reason, infected mosquitoes are being released to prevent the transmission of dengue and other arboviruses. An important question for the long-term success of these programmes is whether viruses can evolve to escape the antiviral effects of We have found that altered the outcome of competition between strains of the DCV virus in However, still effectively blocked the virus genotypes that were favoured in the presence of the symbiont. We conclude that did cause an evolutionary response in viruses, but this has little or no impact on the effectiveness of virus blocking.