The spread and evolution of RNA viruses among honey bees and the wider insect community, with particular emphasis on deformed wing virus (DWV)

• Main Author: Brettell, L. E.
• Published: University of Salford 2017
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.736395

The honey bee is our most significant animal pollinator and is highly valued economically and culturally throughout the world. Unfortunately, over the last 30 years beekeepers across the globe have experienced significantly increased honey bee colony losses, especially in the Northern hemisphere. The spread of RNA viruses, most notably Deformed wing virus (DWV) in association with its vector, the ectoparasitic <I>Varroa destructor</I> mite are now widely accepted as a major factor in these colony losses. This has had a devastating effect on beekeepers and farmers alike. It has become apparent that many of these viral pathogens are generalists, able to infect many insect species. Although much work is currently ongoing in this field, there are areas where knowledge is still lacking, which could provide clues to protecting the bees in the long term. Firstly, I investigated whether there is a unique DWV variant responsible for causing the development of deformed wings by comparing DWV in deformed and asymptomatic bees. This revealed no consistent differences, and greater variation was seen between locations rather than phenotypes, indicating that there is no unique viral variant that induces deformity. Secondly, I disproved, by studying the oldest known <I>Varroa</I>-tolerant honey bee population, the long held theory that <I>Varroa</I> feeding activity induces activation of latent DWV, since these bees have long existed with <I>Varroa</I> yet still harbour low level, genetically diverse DWV infections, and have had no reported colony losses. Thirdly, I discovered two new RNA viruses in ants and wasps collected from apiaries, during a honey bee collection trip to Hawaii. Milololii virus was found to infect the Ghost ant <I>Tapinoma melanocephalum</I>. The other, Moku virus, was sequenced in high depth from yellowjacket wasps, <I>Vespula pensylvanica</I>, but was also, worryingly, at low levels in both Varroa and honey bees, suggesting that it has the potential to infect diverse hosts. Finally, I detected DWV in a range of species living in Hawaiian apiaries. DWV genetic profiles grouped by species rather than location, suggesting that variants may exist which are better adapted to replicate in different host species. Together these increase our understanding of the DWV – <I>Varroa</I> – honey bee nexus, expand our knowledge of the circulating virosphere within the apiary, and provide new insights into how DWV spreads beyond honey bees and into the wider insect community. Further benefit could now be gained from investigating whether DWV and other viruses detected in different arthropod species are true infections by using negative strand – specific RT-PCR to detect viral replication. Furthermore, it would be of great interest to use experimental infections to discover the nature of any pathogenicity of viruses in non - <I>Apis</I> hosts.