Hi all
A very recent publication by Michelle Flenniken & Christina Grozinger brings us up to date on the honey bee virosphere. The situation is nothing like simple:

> Multiple factors influence the transmission, infection dynamics, and pathogenicity of bee-associated viruses. Bees are host to a diversity of viral species and strains. Multiple factors determine whether virus infections in bees remain asymptomatic or result in overt symptomatic infections that cause deformity and/or paralysis or death. Exposure to viruses may be increased in areas with higher populations of bees, and many viruses are readily shared among members of a bee community that forage on common floral resources. Exposure to other parasites, pathogens, and pesticides may hinder bee antiviral defense mechanisms, while access to high-quality nutrition can improve these defenses.

However, they underscore the need to control varroa infestation and suggest that no treatment for varroa leads to much higher winter loss

> The ability of acaricides to reduce Varroa populations in bee colonies—and thereby significantly reduce viral loads—suggests that, overall, beekeepers benefit from acaricide treatment. Monitoring of acaricide-treated and untreated honey bee colonies over the course of a typical beekeeping season in Sweden (March–October) determined that early (i.e., at least six weeks prior to the end of the brood rearing period) treatment with the pyrethroid tau-fluvalinate (i.e., Apistan strips) reduced Varroa mite infestation, which in turn resulted in a 1,000-fold reduction in DWV abundance (92). Furthermore, treated colonies survived the winter, whereas 50% of untreated colonies died. These results illustrate that acaricide treatment can be an effective control for DWV and likely other mite-vectored viruses.

Grozinger, C. M., & Flenniken, M. L. (2019). Bee viruses: Ecology, pathogenicity, and impacts. Annual review of entomology, 64, 205-226.

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