>
>
> >I understood that varroa did not carry viruses but only vectored them
> from one bee to another thus helping to spread the virus.  In other words,
> the bees already had the virus.
>

Before varroa, DWV was a relatively rare virus in honey bees, as it still
is in areas lacking varroa.  I've recently reviewed every study that I can
find on varroa and DWV.  My current assessment is that varroa is most
likely only a mechanical vector, rather than a host for the virus.

Once varroa enters a bee population, there is a rather rapid shift in the
prevalence of various viruses (due to selective pressure), caused by the
introduction of the new vector -- with DWV largely coming out on top.

For a very interesting read, check out:
On the Front Line: Quantitative Virus Dynamics in Honeybee (Apis mellifera
L.) Colonies along a New Expansion Front of the Parasite Varroa
destructor.  https://doi.org/10.1371/journal.ppat.1004323

Even more interesting are a couple of more recent papers detailing how DWV
is normally a rather benign virus in the honey bee, seldom killing pupae:

Tehel, A, et al (2019) The two prevalent genotypes of an emerging
infectious disease, Deformed Wing Virus, cause equally low pupal mortality
and equally high wing deformities in host honey bees.  Viruses 11: 114.

Remnant, EJ (2019) Direct transmission by injection affects competition
among RNA viruses in honeybees.  Proceedings of the Royal Society B
https://royalsocietypublishing.org/doi/10.1098/rspb.2018.2452

 I'm currently in deep discussion with others in an attempt to summarize
our current knowledge on this subject.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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