Alan Sharratt asks about the percentage of Varroa in a colony that will be
found on a Varroa screen at the bottom of the hive.  This depends on the
colony size, how much brood is in the hive, the temperature during your
survey, the overall Varroa population, and how many Varroa are in the sealed
cells at the time that you survey the colony.  I haven't seen any
documentation of the percentage of Varroa in a colony versus brood.  That
information would not be very useful because there are so many differences
between individual colonies, bee behaviors, and environmental conditions at
various latitudes.
 
Here in Washington State, USA, I have been recommending a survey be done in
late February.  If 50 or less mites are found, treat in mid August.  If more
than 50 or 100 mites are found in any one colony treat in late February
(daytime temperatures 50F. or above) for the length of time prescribed on
the label or until you put the first super on, whichever occurs first.  Even
if you can only leave the strips in the hive for two or three weeks in
February/March you will lower the Varroa population significantly, and
probably not experience any colony collapse in the fall.  Use a complete
treatment in mid August (>50F.) after removal of honey supers.
 
Once you treat colonies, you probably can rely on only one treatment per
year if you are in the northern US.  In the UK, follow the Bayvarol label
and any recommendations provided by research, or government agencies.  Don't
rely on beekeeper recommendations because you will here all kinds of them.
That is one reason why many beekeepers in the US are continuing to lose
significant numbers of colonies to Varroa; they don't follow the label, for
economic reasons.
 
James C. Bach
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