Hello Tom and  All,
Tom wrote:
> I am presently working on some beekeeping lectures, and am attempting to
> draw together information on the analysis of infestation by varroa by
> counting the mites which fall to the sticky board through natural causes,
> and using tables to determine if the treatment threshold is reached.

Even those which thought they had the numbers all could use for varroa
threshold are reconsidering. I used Dr. Marion Ellis findings for several
years but at the Tri State meeting he said the threshold issue is more
complicated than he originally thought. I agree with Marion completely.

When you first get varroa as in your case Tom there is one problem which can
not be overcome even with a strip with a 98% control.
Reinfestation through robbing untreated hives.  Many U.S. beekeepers treated
with Apistan three times a year at the start. Others were using one strip to
save money and only once a year. Both the above methods are flawed although
those treating three times a year did not lose hives to reinfestation.

Tom wrote:
> Steve Martin, who issued a Varroa Calculator in the UK, has issued the
> following table

I have still got my varroa calculator but found it very unreliable. Sadly I
know Steve spent many hours working on it. I also found the DeWitt sticky
board unreliable when doing  an average and not counting all squares.

Tom wrote:
> Thus if a daily mite fall of 100 mites were counted in June the estimate
of
> the total mites would be in the region of 3000.

Until a way is found to calculate the amount of varroa in brood cells I find
the above method crude. I will however continue to use the method until a
better method comes along. In my area a hive with a natural mite fall in
June of 100 would be dead by end of August or infested so bad the hive could
not be saved. 100 mites would be at least 3000 mites and the figure could be
as high as 6000 in my opinion. There is no research so all you hear is
mostly theory.

Tom wrote:
> The problem with which I need help is as follows:
>
> Investigations carried out in the UK showed, that if there are more than
> 2500 mites in the colony that immediate treatment is required.

In my opinion the hive needs treatment but researchers in Georgia put the
threshold higher. Others put the threshold much lower.

Tom wrote:
 But I have  data from the Swiss Bee Research to say that if more than 30
mites fall per > day that the colony is heading for trouble.

Anytime you get 30 mites in 24 hours you have got a heavy varroa load which
is bound to climb when bees are at one of their peak brood rearing times in
most of the world..

 This would mean that if the
> above table be used that 900 mites would be the threshold in June.

All depends on the amount of varroa in brood cells, number of frames of
brood and  population of the hive. Our hives are getting close to 60,000
population on 15 frames of brood in June. 900 mites would not be a serious
problem in such a hive.
A hive with 4 or 5 frames of brood and say 30,000 bees might need treatment.
The more you look at threshold the more puzzeled you become.

Tom wrote:
> It would appear essential that if non acaricide treatments are used that
> some reliable data must be available to determine if the colony is headed
> for the threshold to find out if the treatments are working. It would also
> seem important to know this data, to establish if an acaricide treatment
is
> now dealing with resistant mites.

You have got a clear picture of the problem confronting us concerning varroa
threshold. I wish I had better answers for you.

Sincerely,
Bob Harrison