Tom Barrett wrote "I should have said daily mites knocked down by the
application of Bayvarol or Apistan strips - sorry for the omission."
 
Sorry Tom, I think you have made a mistake.
 
The varroa calculator developed by Dr S Martin estimates the total number
of mites in the colony based on the NATURAL mite fall, NOT a mite fall
precipitated by the introduction of Bayvarol or Apistan strips.
 
There is a natural mortality of the varroa mite in the colony and it is
these numbers which are monitored regularly.  In the booklet "Varroa
jacobsoni monitoring and forecasting mite populations within honey bee
colonies in Britain" published by the Ministry of Agriculture ... (MAFF),
it recommends that the mite fall is measured over a period - in summer this
should be 2 weeks and in winter a longer period of 1 month is advisable.
To obtain the daily mite drop, divide the number of fallen mites by the
number of days on which mites were collected.  The booklet does say that
this method is unreliable when the brood nest is rapidly fluctuating in
size (e.g. swarming), small (less than 5,000 brood cells) or collapsing.
 
For those who have attempted to count varroa mites in the floor litter, the
following practical tip may be useful.  If you scrape the total floor
litter (collected below the varroa screen / floor) into a glass or plastic
receptacle and then pour methylated spirits onto it, the varroa mites (and
any other bee parts made of chitin) float to the surface.  All of the other
debris, such as pollen, wax, etc. remains at the bottom i.e. doesn't float.
This method is very much less time consuming that fishing through all the
debris!
 
Apologies to our bee friends outside the UK, but I am not sure whether
methylated spirits is a description you will be familiar with.  Perhaps
someone else can help with the name of an equivalent product.
 
Bill Parker
Hobbyist Beekeeper
Buckingham, UK