As promised, here's a summary of Tom Seeley's talk on feral bee populations in Arnot Forest (4200 acres near Newfield, NY).
Tom did a feral bee survey in 1978, and again in 2002, 2003, 2004. He used bee lining techniques in all years. He found about the same number in 2002 as he did in 1978, much to everyone's surprise. Moreover, he found that although about 25% of colonies are typically lost over the winters, they are coping quite well without medications of any sort.
He set up a couple of bait hives in the forest so that he could examine populations for varroa. He found that the colonies indeed have mites, but that unlike our typical colonies, the mite drop count does not peak in late summer/fall. He tested right through to October, and a 48-hour mite drop showed about 20 mites per colony pretty consistantly through season.
For this coming season, he will test three theories: A. The bees have genetically adapted; B. The mites have become avirulent (meaning that they have adapted not to kill their hosts) or C. Frequnt swarming or some other environmental variable is at work in these colonies.
He will do this by breeding "Arnot Forest" queens, and setting up an apiary with plain old Cornell Lab bees and their mites and "Arnot Forest" bees. If it is bee genetics, the Arnot Forest bees should show similar resistance to the mites. If the mites of the forest have adapted, then moving the bees to an apiary where they'll meet "plain old Cornell lab" mites should show up in typical mite build up numbers. If it's frequent swarming or another enviromental factor rather than bee genetics, then the Arnot bees won't fare any better than any other bee once in an apiary.
I'll keep you posted when I hear the results of his experiments.