Pete, when I was developing my mite population spreadsheet*, one of biggest
surprises was the profound effect of mite immigration in fall.  I used
numbers from the paper that you cited (as well as others) as variables in
the model.  Keeping bees near sources of mite immigration completely
changes fall varroa management!

Those of us who kept bees through the initial collapse of feral populations
due to varroa remember the effect well--our colonies, made nearly mite-free
by application of Apistan strips, were simply overwhelmed by an influx of
mites from the collapsing feral colonies.

Today, the same likely happens in urban areas containing large numbers of
treatment free beginning beekeepers.  As their colonies collapse from
varroa, they flood the neighborhood with mites by drifting and robbing
behavior of bees.

What I don't understand is the full effect of distance between hives.
Frey's 2011 study suggests that invasion takes place equally to hives up to
1 mile distant.

On the other hand, Seeley's** study suggests that hive separation of only
100-250 feet made a large difference.

If constant invasion via drifting is actually that common between
closely-spaced hives, then it's hard to understand why mite levels vary so
greatly from hive to hive in the same apiary.  Or perhaps this constant
invasion masks the presence of actual mite resistance in some hives.

 *
http://scientificbeekeeping.com/sick-bees-part-12-varroa-management-getting-down-to-brass-tacks/

**
https://portal.nifa.usda.gov/web/crisprojectpages/0223284-sustainable-solutions-to-problems-affecting-bee-health.html

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

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