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.