Continuing, “varroa virulence” should more properly be thought of as the virulence of the associated viruses. In this case, it is the extremely high rate of replication and the crowding out of competing viruses that makes this variant so virulent. (sorry about the alliteration, couldn’t be avoided)



In experiments

on individual Varroa-exposed pupae we demonstrate

that a single type of virulent DWV is amplified 1,000–

10,000 times in the recipient pupae, despite the mite

containing a high diversity of replicating DWV strains.



Our results indicate that a virulent recombinant form of DWV,

while transmissible orally, only replicates to high levels when

directly inoculated into honeybee haemolymph – by Varroa or

experimental injection. This results in massive reduction of DWV

diversity in bees with high virus levels, both in the Varroa-exposed

pupae and newly emerged bees with symptomatic deformed wing

disease. Significantly, the same virulent recombinant form of

DWV reached the highest levels in mite-exposed pupae and in

adult bees exhibiting characteristic deformed wing symptoms.



Although exposure to Varroa resulted in changes in expression of a

number of immune-related genes, the roles of which should be

further explored, we demonstrate that it is the route of virus

acquisition that is responsible for the amplification of this virulent

form of DWV in a Varroa-infested colony.







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