I have seen fluvalinate fail us in the 90's and after a hiatus of some years, become once again effective in economically reducing the mite 
population. 
I would think that the non-resistant mites breed back into our gene pool and the general mite population at a future date succumbs to the miticide.
So one could surmise that a miticide's effectiveness for varroa control isn't chiseled in stone. 
k

 Kirk Jones

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