>
> >Are there other references/experiences about treatment thresholds?
>

There is  good graph in the following paper from Germany.  Colony winter
mortality rises sharply at somewhere around 5 mites per 100 bees.

"Plotting colony mortality
against ‘varroa mites per 100 bees’ revealed
that with as little as 10 mites per 100
bees around 20% of the colonies were prone
to collapse over winter and an average of
50% mortality could be expected if more than
20 mites per 100 bees were present in a colony
in autumn (Fig. 5). However, some of the
colonies with high infestation rates of more
than 30% in October were able to survive the
winter"


> Genersch, E., von der Ohe, W., Kaatz, H., Schroeder, A., Otten, C., Berg,
> S., Ritter, W., Gisder, S., Meixner, M., Liebig, G., Rosenkranz, P., 2010.
> The German bee monitoring project: a long term study to understand
> periodically high winter losses of honey bee colonies. Apidologie 41,
> 332–352.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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