> What we do not know is what type of drop will a lighter dose provide?

At some posts about oxalic there was pointed that a lot more experiences is 
in Europe. That might be true. I wrote a story '10 years of oxalic use' in 
our bee magazine last year.

In 1997 - 1999 the basic research about oxalic acid use was done. The work 
was done as group research. People from different countries agreed on the 
tests and the methods. This way it was possible to test many variations in 
different situations. First tests concluded that oxalic+sugar+water worked 
much better than just oxalic and water. This is most likely because water 
solution dries much faster in the hive.

Then next year we had test for different concentrations. In the end the dose 
75 g oxalic + 1 kg sugar + 1 litre water gave most consistent results for 
90 - 95 %mite drop in hives without brood. 50 g worked too but results 
averaged about 85 % drop, but variation is big. That why 75 grams was 
recommended for use. There was also follow up for spring development. In 
these results differences were not big, but 50 gram group tended to have 
more bees. No statistical difference.

As a advicer I always recommend the beekeepers to mix like this: 75 g oxalic 
+ 1 kg sugar + 1 litre water. Easy to remember. To use ready sugar liquid is 
more work cleaning the measuring cup than making it with water and dry 
sugar.

My friend is going for resistant bees and he gradually stopped oxalic 
treatments. From his data we saw that oxalic gave surprising good drops of 
mites with just 10 ml/ big hive. If you give the same small amount of oaxlic 
in more diluted solution t will not work as well.

So in summary I would say that you can give less than recommended oxalic 
treatment and still get reasonably good results, but variation in efficacy 
will be bigger than in recommended amounts.

During last few years the trend here has been that many are going for fall 
and spring treatment with tricling. This way they use only oxalic against 
varroa. Spring use is just after first flight before the bees start to raise 
brood in bigger amounts. Some years you can treat in spring without any 
brood, but time window is small.

Treating twice in fall will result in big problems. It was hard for me to 
believe that bees that can not tolerate 2 treatments in fall with 1 - 2 
months apart, do tolerate treatment in November and again in March. It must 
be in more time and chance to fly.

I have treated 80 % of my own bees this fall, and need to do the rest fast 
before winter really starts.

Ari Seppälä

Finland

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