Hi:
 
The discussion on border closing and the history has been interesting.
In Montana, we first saw both mite species in colonies of migratory
beekeepers.  First a few, now virtually all (as far as I can tell) of
these operators.
 
In spite of regular treatment with strips, etc., we have no problem finding
either mite.  Until recently, most of our hobbiest and non-migratory commercial
beekeepers have been free of Varroa, although Tracheal mites became more
or less endemic.  Packages or queens bought in the last 2-3 years are
one potential source of introduction of T. mite to the colonies
maintained by these beekeepers.
 
This year, we have begun to find Varroa in hobbiest and
non-migratory operations.  Based on discussions with the beekeepers, I
think hived swarms are a likely contributor to the problem.
 
We suggest treating any swarms to suppress mites - the swarm may be a
consequence of the natural division of a strong, healthy colony.
 
However, the swarm may be from an infested colony that absconded from
their hive.  We have observed this response and have heard other reports
of this happening.
 
So -- a swarm may be a colony that left its hive.  Why remains unknown.
Perhaps it is a desperation move to purge the colony of mites.  Possibly
the mites influence bee behaviour, maybe as a means of enhancing
dispersement.
 
Whatever, swarms should be regarded as a likely source of mites.
 
Jerry Bromenshenk
The University of Montana
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