a Mr Borst snip.. 
“Many backyard beekeepers don’t have any varroa control strategies in place. We think this results in colonies collapsing and spreading mites to neighboring colonies that are otherwise well-managed for mites,” said Nathalie Steinhauer, a graduate student in the UMD Department of Entomology who leads the data collection efforts for the annual survey. “We are seeing more evidence to suggest that good beekeepers who take the right steps to control mites are losing colonies in this way, through no fault of their own." 

[Comment: I have been promoting this viewpoint but I wonder whether there is any science based evidence of it.]

my comments...
I think we have been down this road before?  And I have previously asked exactly the same question.  The only evidence in that thread as far as I could tell was that migrating varroa tended to be attracted to hives already HEAVILY infected.  This suggest to me something other than cross contamination from untreated hives.... specifically varroa treatments that have become ineffective or are improperly applied (either due to technique or timing).

I am especially suspect of claims without proof that toss the blame on to someone else...  

imho a clue is good but hard evidence is better...

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