I can't make a judgement on the time scale for co-evolution. 
I would bet that when I put preventive treatment and mixing mites and bees continuously in a theoretical model, the time to a tolerant bee/mite couple would be prolonged. 
 
We got Varroa here in the early 80ties...I like to imagine what could have happened when we had done 30 years ( alot of mite generations) of IPM and selection in stead of just treating everything and select for yield and non-aggression mainly.
 
Lennard
 

> 1. varroa does not reproduce in the worker brood of cerana therefore 
> limiting reproduction to only times when the colony is producing drone 
> brood. 2. swarming. Cerana swarms more than any race of bee I have been told which 
> limits varroa. 3.cerana keeps an opening in drone cells from which to extract varroa from 
> cells.
> 
> Mellifera is not known for any of the above and not likely to change any 
> time soon .
> 
> A bee which can handle varroa (untreated) as managed in commercial 
> operations today seems unlikely but we must remain optimistic.
> 
> bob 
 		 	   		  
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