The mite density numbers reported from "resistant" colonies presumably produced by natural selection are not impressive.  In a commercial setting, colonies with those numbers would not perform well or be dead.  This leaves a lot of room for skepticism that natural selection can quickly lead to commercially useful colonies. 

In an odd irony, the fact that these possibly partially resistant colonies harbor mite levels that harm them, could be leading to some kind of "sustainable" coexistence between host and parasite.  If a moderate infestation prevents colonies from growing fast, producing a lot of brood and drones, limping along may prevent explosive growth of mite populations, allowing some to survive.  The dead ones are forgotten and not counted.  Those limping along are called naturally resistant.

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