Dwv

[Stromnessbees]

You need to read to paper to see how the arrival of varroa promotes the single most virulent strain of DWV at the expense of other strains of DWV which are less harmful to bees.

CCD cases in the US occured more than ten years after the widespread use of neonicotinoids in the US. No correlation there at all.

The correlation is actually very good:

In the 1990s Imidacloprid was introduced, and we didn't hear much about adverse effects.
But around 2004 Imidacloprid was replaced by Clothianidin, which is three times as toxic to bees as Imidacloprid.
I assume that this triple toxicity was not taken into account when it was introduced and the bees were hit hard by this new type of neonicotinoids, resulting in massive occurrences of CCD, which is exactly what is to be expected from the way this neurotoxin works.

When the pesticide companies realized that they had done an 'overkill' they reduced the Cothianidin concentrations on the seed coatings again, so outright CCD is not observed as often anymore, but bee colonies in proximity of treated fields suffer reduced vitality, become susceptible to secondary infections and are likely to have queen problems.