One would think that inter-colony transmission of mites might (other than
in the case of rob outs) be greatest between adjacent hives in an apiary,
due to the well-measured degree of bee drift between adjacent hives.

We've had the opportunity to test this hypothesis this week.  We modified
our motorized alcohol wash shaker table to set in the back of the truck and
run off a voltage inverter.  This allows us to rapidly and accurately
process alcohol washes in each yard, as the motorized washer eliminates any
hand agitation error, and gets a confirmed 100% recovery of mites.  It also
cut way down on processing time--the three of us can take samples, process,
record, and clean up a yard at the rate of one wash every minute and a half.

In the past three days, we've performed  alcohol washes  of all hives in
seven apiaries (over 150 in total).  It is not at all uncommon for one or
more colonies in a yard to have mite counts far above the norm.  Here are
values for four yards (n = number of hives; median mite count; highest mite
count).

n Median High 20 2 9 31 4 50 20 8 39 24 4.5 38

The high mite counts were typically outliers, obviously far above the
medians.  Strikingly, there appears to be no relationship between mite
counts in adjacent hives.  The counts for colonies adjacent to colonies
with counts near 40 are often zeroes or 1's.  I have no idea whether that
is due to those low-count colonies being more resistant, but it certainly
indicates that they are not being overwhelmed by mites from the hive next
door.

But if those outliers were allowed to crash, a proportion of their mites
could be quickly dispersed by robbing.

What I'm seeing is the need in any breeding program for mite resistance to
cull the queens from those high outliers, and to further track the
performances of those colonies with zeroes and 1's.  This is similar to the
method employed by the Baton Rouge lab, in which they start groups of
identical package colonies, headed by queens to be tested, and track mite
buildup over time. Similarly, we start our entire operation each spring
with roughly identical nucs with low mite levels.   I'm hoping that with
our newfound ability to screen across our entire operation for colonies
exhibiting low mite levels, that we may be able to improve our selection
process.

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

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