A Rickettsiella transinfection in Rhopalosiphum padi reduces fitness and alate production but not plant virus transmission

Native bacterial endosymbionts in aphids have been studied for many years but it is only recently that transinfections across species are being investigated from an applied perspective. Here we consider the impact of a Rickettsiella viridis transinfection from the pea aphid (Acyrthosiphon pisum) in an important pest of cereals, Rhopalosiphum padi, that causes feeding damage and transmits barley yellow dwarf virus (BYDV). The transinfected strain had fitness costs in its new aphid host (with an rm around 20% lower), and showed horizontal transmission. Rickettsiella did not transmit vertically with complete fidelity although it persisted in population cages for at least 11 weeks. While Rickettsiella did not affect transmission of BYDV, it reduced the production of alates by 10% or more depending on aphid density. The aphids carrying Rickettsiella showed a slower rate of movement to adjacent plants compared to those without Rickettsiella. The body colour of aphids with Rickettsiella was darker. These findings point to a transinfection with deleterious host effects and a potentially reduced movement capacity with an ability to persist in populations.