There is another well-documented example of unmanaged colonies with
varroa, although these colonies were located close together.

Hi Adony
   This is exactly what would be expected in a nordic climate.  What you're
doing is allowing the hand of selective pressure to shift the mite's
reproductive strategy from horizontal transmission to vertical transmission
(colony to colony by collapse, vs. parent colony to daughter colony by
swarming), plus selecting for mite tolerant bees.

It is a coevolution taking place.  The key requirement is a nordic climate
where mite-stressed swarms all die, where mite-stressed colonies don't
swarm, and, most importantly, where colonies collapse during cold periods
when no robbing takes place, thus eliminating horizontal transmission of
mites.  The only mites that are able to survive for multiple years are those
that don't cause colony collapse.  The only bees that survive are those that
can tolerate a low level of mites.

I would expect a situation as in Gotland to be the perfect place to find
varroa and the EHB to establish a stable host-parasite relationship.
Beekeepers in northern climes, where mites are not horizontally transmitted
through robbing, are the most likely to experience a stable mite/bee
relationship.

In areas where major chemical control is practiced, the majority of mites
that pass on their genes are those that cause a colony to collapse.
Beekeepers there are inadvertently selecting for mites that cause colony
collapse, since that would be the most mathematically efficient way to pass
on their genes.

Randy Oliver

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