A plant pathogen-mediated interaction between an aphid vector and its parasitoid

Plant pathogens that are dependent on arthropod vectors for transmission have been shown to boost vector performance and survival, which may indirectly increase pathogen prevalence. In this context, our objective was to assess the influence of a vector-borne plant pathogen, barley yellow dwarf virus (BYDV), on the susceptibility of its vector, the bird cherry-oat aphid Rhopalosiphum padi, to a parasitoid, Aphidius colemani. We compared the susceptibility of virus-free aphids to that of viruliferous aphids by exposing populations of aphids on wheat plants to A. colemani parasitoids for 24 hours. After this time, we determined the percentage of R. padi parasitized by A. colemani and the percentage of A. colemani mummies from which adults successfully emerged. We found that the virus status of the vector influenced its parasitism rate, as viruliferous aphids were parasitized more frequently than virus-free aphids. However, the percentage of mummies from which A. colemani adults successfully emerged was equivalent for both virus-free and viruliferous aphids. Unlike previous studies that found greater or unchanged vector performance in the presence of a plant pathogen, we observed increased rates of parasitism and enhanced vulnerability of viruliferous aphids to a natural enemy. Therefore, where A. colemani parasitoids are abundant, the spread of BYDV may be limited by the greater vulnerability of viruliferous R. padi.