The problem is a complex one.
We have observed repeatedly that bees that seem adapted to varroa in one location have been vulnerable when moved to other regions.
Not only do the bees have to be able to handle varroa, but they also have to be able to survive other threats and perhaps the selection, natural or guided, selects against other essential traits and reduces general fitness.
That is not necessarily the case, but is IMO probable and must be considered..
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