> I have never known, from personal experience,  DWV to be independent of mite levels.

Not sure how you would know this. Viruses are generally present but do not usually produce visible symptoms. Bumble bees can have DWV, without varroa (varroa does not infest bumble bee nests).

> The majority of well-characterized bee viruses are picorna-like RNA viruses, which may be maintained as covert infections or cause symptomatic infections or death. Second to honey bees, the consequences of bee virus infections have been most investigated in bumble bees. DWV replicates in multiple bumble bee species, though symptomatic infection has only been described in B. terrestris. Bombus terrestris exhibits DWV-associated wing deformities and mortality.

Recently identified bee viruses and their impact on bee pollinators
Alexander J McMenamin, and Michelle L Flenniken
Current Opinion in Insect Science 2018

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