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Subject:
From:
Komppa-Seppälä <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Fri, 8 Apr 2005 17:02:20 +0300
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allen:
> Have you any experience with applying oxalic more than once in the fall by
> dribbling (also called drizzling)? I heard some rumours that more than one
> treatment per generation of bees could have bad effects, but nothing very
> certain in that regard.
>
> I had also heard that multiple treatments by evaporation did not have bad
> effects.

Being  non -native English speaker I might be wrong with my dribbling. What would be the exact right term for treatments with oxalic in sugar solution  ?  Not sprayed, but dropped on bees as small drops from the top of the hive( I use 50 ml plastic syringe without needle).

Allen is right, oxalic used this way will kill bees if used twice during the fall. I would say based on my few mistakes in notes that hives treated twice in fall had 30 % less bees in spring than normal.  I have heard stories that  20 - 40  % of the double treated hives  died during winter. For some reason no one wants to make a study about this in large scale :). But so many people have tried that I feel 100 % sure to say that double treatments in fall should not be done.

Effect on bees  does not have to do about the generations, because we have trials going on with double treatments. Once in the fall when last brood has emerged ( November) and again in spring maximum of 2 weeks after the cleansing flight ( early April). Exactly same adult bees in the hive at both times.  At this time bees are only starting to generate brood. Average hives have capped brood area that can be covered by one open hand.  We try to see if the varroa stays in control by only these treatments. The figures from first year seem fine. The Danes have also tried fall - spring treatments and  they also say that colonies have same populations when compared to untreated ones.

I admit  that this kind of treatment quite often kills 20 - 30 bees immediately after the treatment. This can be seen by the entrance next morning.

Evaporation does not affect the same way. It can be done on weekly basis during fall. But we have only experience from 3 - 4 evaporation treatments per hive during fall . The last one should be after all brood had emerged.

Ari Seppälä

Finland

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