Tom

The problem is not the mites per se, it is the viruses for which they act as
vectors.  Thus a colony can tolerate very high levels of mites if viruses
are absent, but will have severe problems with lower numbers of mites where
viruses are present; the important virus here is Deformed Wing Virus (DWV).

Since we (your average beekeeper!) have no way of monitoring viruses, we
have
to assume that they are present and therefore act to keep varroa numbers as
low as possible.  2500 may be a threshold where viruses are present, whereas
10,000 may be tolerated where they are absent.  I think that this explains
some of the apparent inconsistencies in the recommendations.

See my report on the Central Association Weekend in:

http://www.stratford-upon-avon.freeserve.co.uk/Newsletters/February2002.htm

Peter Edwards

----- Original Message -----
From: "Tom Barrett"
Sent: 14 April 2002 12:16
Subject: Mite thresholds

> Investigations carried out in the UK showed, that if there are more than
> 2500 mites in the colony that immediate treatment is required. 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
> Perhaps this difference is explained by differences in climate between the
> UK and Switzerland or perhaps there is some other explanation, eg both
> figures are incorrect.