Invasion of Varroa mites into mite-free colonies at a military training area.
E. Frey, P. Rosenkranz (Apicultural State Institute, University of
Hohenheim, 70593 Stuttgart, Germany)

Honey bee colonies should be treated against varroosis in late summer
to guarantee the production of healthy winter bees. However, the
invasion of Varroa mites from non-treated colonies may wreck the
treatment effect. To quantify the invasion rates we used a former
military training area which is not accessible to other beekeepers.
Four heavily Varroa infested honey bee colonies served as "donator"
colonies. In distances of 1, 30, 400, 1300 and 1500 m from the donator
colonies we placed two mite-free monitoring colonies each which were
continuously treated with different acaricides. The "mite free status"
was confirmed by the analysis of bee and brood samples.

From August–October 2006 the number of Varroa mites on the bottom
boards of the monitoring colonies were counted at weekly intervals to
record the Varroa invasion rate. The average Varroa infestation rates
of the adult bees in the "donator colonies" increased from 18% in
August till 38% in October. Two colonies died at the beginning of
October due to the high Varroa infestation. In total, 2029 mites were
recorded in the bottom boards of the 10 monitoring colonies during the
8-week period.

The average invasion rates per colony were 283 at 1 m distances from
the "donator colonies", 201 at 30 m, 155 at 400 m, 122 at 1300 m and
255 at 1500 m. Under normal beekeeping conditions the density of bee
colonies and, therefore, the invasion pressure would be considerably
higher. Our data confirm that highly infested colonies represent a
risk for treated colonies over distances up to 1.5 km. For beekeeping
practices, the treatment of all colonies at the same time during the
late summer period is an urgent need for treatment concepts.

* * *
comment:
Our authors don't speculate on how the mites are transferred, but if
it is by robbing, then you would expect them all to have about the
same amount, whether the distance is a meter or a mile. That's seems
to be what they found. The colonies averaged about 200 with a range
from 122 to 283

-- 
Peter L. Borst
Danby, NY  USA
42.35, -76.50

picasaweb.google.com/peterlborst

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