Failure of OA treatment can be explained by the following:
1. Failure of sublimation treatment:
        1. The bottom board or the screen for screened bottom board is clogged with dead bees. There is no room for OA fumes to go through and OA fumes will become crystals right on the surface of dead bees.
        2. Too much brood that have many mites
        3. bees robbing failing colonies full of mites
2. Failure of OA drench treatment:
         1. Treatment of OA solution on the top box at time most of the bees in the bottom box. Our research showed efficacy goes down to 60% in comparison to splitting the application one half on top box and one half on the bottom box. Beekeepers hate to split hives to have access to bottom box for application at this time of the year fall.
        2. Too much brood that have many mites
        3. bees robbing failing colonies full of mites

Of course in this case Formic acid, thymovar, or apilifevar will provide higher efficacy as long as there is enough ambient temperature (above 15C day time and not less than 10C at night time).


Medhat

Dr. Medhat Nasr
Alberta Provincial Apiculturist
Pest Surveillance Branch
Research and Innovation Division
Agriculture and Rural Development
17507 Fort Road NW
Edmonton, AB T5Y 6H3 Canada
Tel: 780-415-2314             Fax: 780-422- 6096
E-mail:  [log in to unmask]


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