There is a lot of evidence that while varroa treatments are necessary to control varroa, that these treatments may prevent the colony from recovering full health. Also, they point to the fact that merely controlling varroa is not sufficient to control the viral infection. This can lead to colony collapse even where varroa are no longer present.

> This study shows a clear trend of rising viral titres in bee populations over the course of a season from spring to autumn. Despite the application of acaricide, varroa mites and viral titres continued to rise while remaining below the levels observed in the untreated group. In many cases, the treatment only helped to control varroa loads and viral titres to a limited extent, and led to no significant reduction in the prevalence of virus-sick bees.

> In part, this may be explained by the recent findings that show negative impact of acaricides on honey bee immunity. It has been noted in several studies that DWV reduces the lifespan of overwintering workers often in connection with varroa mites. DWV has also been suggested to lead to colony losses independent of varroa infestation possibly in synergy with an uncharacterised stress factor. Thus, we hypothesise that the effect of treatment may constitute this stress factor.

> Varroa mites are the driving factor that has led to an upsurge in viral titres. Beekeepers implement various treatment regimes against varroa mites to prevent colony losses, which in turn lead to persistent viral infection in the colonies. The immune-suppression resulting from pesticide usage in the hive linked with the higher prevalence of viral infections may result in sudden colony loss. Beekeepers often experience low efficacy after years of recurring treatments. This subsequently leads to more aggressive treatment methods resulting in an unsustainable warfare on varroa mites, also detrimental to bee health.

Francis RM, Nielsen SL, Kryger P (2013) Varroa-Virus Interaction in Collapsing Honey Bee Colonies. 
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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