There are two broad approaches to breeding bees that can deal with varroa.
One is resistance (inhibiting mite reproductive success); the other is
tolerance (being able to tolerate the presence of the mite).
Tolerance is mainly about dealing with the mite-associated viruses.

We observe colonies that can exhibit very high mite loads, yet don't show
signs of morbidity due to DWV or other viruses.  However, we don't select
them as breeders, since they did allow mites to build up to high levels in
the first place.

We do select for mite resistance, the rationale being that if there aren't
many mites in a hive, then viruses typically aren't a problem.
Under natural selection, such as at Gottland, a combination of traits
conferring both resistance and tolerance may the the end result.
Unfortunately, such bees may not be anything that you'd want to keep.
Survivors, yes. Gentle, non-swarmy, and productive, perhaps not.

In my own selective breeding program, it appears that you can have gentle,
productive colonies that are also very strongly resistant to varroa.  I've
been tracking a group of them for 19 months now, none having been given any
treatments.  I've got 7 colonies that have maintained minimal mite loads
over the entire 19 months.  Some of them are beautiful, gentle, productive
hives.  Time will tell if those traits are heritable.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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