Hi all
I just got a note from BeeInformed. They sampled one of my hives and checked for the usual suspects. The level of DWV in that hive was in the 90th percentile. The cited level was 741.5 billion copies. Nosema was 4.6 billion copies (below the 30th percentile). The hives were all treated twice with MAQs during the summer.  I dug up some info on DWV:

DWV drastically shortens honey bee lifespan (the following is from 2011)

> Colony levels of infection with the parasitic mite Varroa destructor and individual infections with DWV were also associated with reduced honeybee life expectancy. In sharp contrast, the level of N. ceranae infection was not correlated with longevity. In addition, vitellogenin gene expression was significantly positively correlated with ABPV and N. ceranae loads. The findings strongly suggest that V. destructor and DWV (but neither N. ceranae nor ABPV) reduce the life span of winter bees, thereby constituting a parsimonious possible mechanism for honeybee colony losses.  


There are strains of DWV that are worse than others (2016)

> Using laboratory experiments and a systematic field survey, we demonstrate that an emerging DWV genotype (DWV-B) is more virulent than the established DWV genotype (DWV-A) and is widespread in the landscape. Furthermore, we show in a simple model that colonies infected with DWV-B collapse sooner than colonies infected with DWV-A. We also identify potential for rapid DWV evolution by revealing extensive genome-wide recombination in vivo. … colonies collapse 1 year earlier when infected with DWV-B when compared with DWV-A.


DWV may not show any visible symptoms, they may be “covert” (unpublished, dated 2017)

> DWV is named after the characteristic wing deformities that can arise when honeybees are infected in the larval or pupal stage via the ectoparasitic mite vector Varroa destructor . In this case, virus infections result in bloated abdomens, miscolouring and shortened life spans. Typically, however, infections take on a more “covert” form, resulting in no visible morphological symptoms, especially when infection occurs in the adult stage or when mites carry only low virus titers. Nevertheless, the fact that colonies with covert infections can suffer from weakness, depopulation and sudden collapse and that the presence of the virus has been linked with both winter mortality and colony collapse suggests that DWV exerts a significant amount of long-term stress.

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