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<p>Abstract</p> <p>Background</p> <p>Insect symbionts employ multiple strategies to enhance their spread through populations, and some play a dual role as both a mutualist and a reproductive manipulator. It has recently been found that this is the case for some strains of <it>Wolbachia</it>, which both cause cytoplasmic incompatibility and protect their hosts against viruses. Here, we carry out the first test as to whether a male-killing strain of <it>Wolbachia</it> also provides a direct benefit to its host by providing antiviral protection to its host <it>Drosophila bifasciata</it>. We infected flies with two positive sense RNA viruses known to replicate in a range of <it>Drosophila</it> species (Drosophila C virus and Flock House virus) and measure the rate of death in <it>Wolbachia</it> positive and negative host lines with the same genetic background.</p> <p>Results</p> <p>Both viruses caused considerable mortality to <it>D. bifasciata</it> flies, with Drosophila C virus killing 43% more flies than the uninfected controls and Flock House virus killing 78% more flies than the uninfected controls. However, viral induced mortality was unaffected by the presence of <it>Wolbachia</it>.</p> <p>Conclusion</p> <p>In the first male-killing <it>Wolbachia</it> strain tested for antiviral effects, we found no evidence that it conferred protection against two RNA viruses. We show that although antiviral resistance is widespread across the <it>Wolbachia</it> phylogeny, the trait seems to have been lost or gained along some lineages. We discuss the potential mechanisms of this, and can seemingly discount protection against these viruses as a reason why this symbiont has spread through <it>Drosophila</it> populations.</p>