Hugo Thone wrote:

> These figures for natural fall seem extremely high to me.
> I have been monitoring natural mite fall this summer during
> approx. 2 months : I counted max. 5 mites/hive/week
> (I was not using sticky boards).

The natural fall numbers that have been used is based on using a
sticky board placed on the bottom board of a bee hive without any
chemical treatment. The level of mites that require treatments vary
from on location to another. Therefore, research needs to be
conducted in various locations to find the economic threshold and
timing for treatment.
Mussen recommended  treatment in California, USA if August
insert yield 20-200 mites/24 h /day. Hoopingarner in Michigan
recommended summer treatment if >10 mites found on sticky
boards within 24 h. Delaplane and Hood justified treatment in August
in Georgia and South Carolina, USA if number of fallen mites reach
117 mites/day. In Ontario Nasr and Mcrory recommend treatment in
late August-early September when fallen mites is 50-120 mites/day.
These mentioned figures can be used as a guide line for starting the
treatment of bee colonies. Thus, we can avoid treatment according to
the Calender which in some cases may be too late or too early. The
purpose of treatment is to protect bees from varroa mites, to have
enough time to make honey and harvest the honey, and to ensure
having healthy bees for the winter.

Cheers

Medhat Nasr
Medhat Nasr, Ph.D.
Research Scientist,
Ontario Beekeepers' Association
Dept. Environmental Biology
University of Guelph
Guelph, Ontario, Canada
N1G 2W1
Tel: (519) 824-4120
Fax:(519)837-0442
e-mail: [log in to unmask]