Hi all,
It would seem likely that drone brood trapping of varroa would select for mites with a preference for worker brood as Stan pointed out.  However, the reproductive rate of varroa is much lower in worker brood and that may actually be enough to allow the colony to coexist with the mites.  I seem to recall an article to this effect from somewhere in Europe where the mites prefered worker brood and as a result did not build up to damaging levels in the colony.  The difference in that case was shown to be the mites not the bees.  If this is true - a big if - the selection resulting from drone brood trapping is also to the beekeepers avantage as it would at least reduce the need for treatment due to the lower reproductive potential of the mites in worker brood.  
 
FWIW
 
blane
*************************************
Blane White
MN Dept of Agriculture
St Paul, MN