Garth wrote:
 
> I have another theory. Old hives get cells which are packed with many
> layers of silk and the bees from these hives are smaller than from
> younger hives. The bees also would in theory hatch a bit faster due
> to the smaller size. Hence the mites would have to stay on the
> drones as they would not be able to complete alife cycle on the
> worker brood.
>
 
I doubt the small cell or the infrequent handling theory mentioned in
another post. Just a few years after the onset of varroa there are
practically no feral colonies here in Western New York. Farmers and long
time residents have told me of bee trees that have been around for many
years, were always populated and are now dead. Gardeners and vegetable
farmers tell us there are no bees visiting their crops. It seems likely
that  many of these colonies had small cells as you mentioned and bee
trees are seldom disturbed by beekeepers.