Oxalic acid Vaporiser
In the autumn of
2002 I start to find Varroa mites in my hives. It is time to get a system
up and running to control the mites. Apistan is still working in Sweden,
we have banned all import of bees for many years and managed to keep
fluvalinate resistant mites from crossing the borders. However, that
is not going to last forever. We will sooner or later develop resistant
strains here too. Difference to most other countries it is only commercial
beekeepers who are allowed to use Apistan strips. This means alternative
treatments are developed for hobby beekeepers wich are not using chemicals
that will affect the environment.
Organic acids has
showed to be useful in fighting Varroa mites. Formic acid was
first used, but have some drawbacks when it's very temperature dependant.
Oxalic acid treatment is now being developed, but has the disadvantage
it doesn't kill mites in capped cells. So the treatment has to be applied
in autumn when there is no brood in the hives. In a climate like lat.
60 with short summers (brood rearing period) it might be possible to
keep mite population under control this way together with drone removal
in the spring.
When Apistan (the
only allowed insecticide) is quite expencive, there is also the possibility
tof cutting cost that influence the decision to look for alternative
treatments. One of them is the Varrox vaporiser developed in Switzerland.
This is only a first test and I hope to be able to report better result
Varrox vaporiser, made by Andermatt Biocontrol AG. www.biocontrol.ch.
It's a small pan that's heated by 12 volts and melts and vaporise
the Oxalic acid crystals.
When I'm using
Styrofoam hives with ventilated mesh bottoms, I want to be able
to use the vaporiser without having to open the hive to first close
the mesh bottom. Instead I made a device to put under the hive and
let the vapors go up through the mesh.
I will need
6 of them when each hive should be closed for 15 min after treatment
to allow vapors to spread inside.
Making a test
in the open to se how it works before doing a treatment to any hive.
1 gram of oxalic
acid (C2H2O2*2H2O) in the Vaporiser. One gram is used per Langstroth
Next step is
to connect the Vaporizer to a 12 volt car battery.
acid crystallz are melted and vaporised.
are also rising through a mesh in floor.
Now I test with
a box containing frames but no bees. This is to find out how well
the vapors will spread in the box.
closed during treatment.
The lid is taken
off the empty hive after treatment with one gram.
As you can see
on this picture there is a layer of oxalic crystalls on the top
So time to do
the real test on some hives.
Front of the hive is easily lifted and the "vapor bottom"
is installed under bottom board.
Pan on the Varrox
is filled with 1-2 grams of oxalic crystalls.
One gram per Langstroth deep box.
takes 2,5 minutes, then the hive is left sealed up for another 15
minutes to allow fumes to spread inside.
After a day
there started to fall varroa mites to the bottom of the hives where
I have the collecting tray. On the picture there is 3 mites and
a braula (Bee louse).
There is a slower
rate of falling mites than with Apistan. Mites keep on falling down
for 4 weeks at a steady rate before I can see a reduction. At this
point I inserted Apistan strips to get a measure of the mumber of
mites still in the hives.
This study was done
late in the autumn 2002 whith temps near frost. Only a few hives have
been used, and bees has been in cluster with very little movement. This
is probably giving a slower rate of mite fall due to less movement of
bees in the hive, and thus exposure to the oxalic crystalls. The final
Apistan treatment show a minor increase from the earlier mite fall after
oxalic fumigation. To properly evaluate oxalic vaporization the hives
would have to be monitored over a period of at least 6 weeks before Apistan
treatment or other ways of counting remaining mites is applied. From a
very rough estimation it looks like there is at least 80% efficiency.
The Varrox vaporiser
gives similar results in my climate as trickling sugar solution with 3,2%
oxalic acid.The amount of pure oxalic is the same per hive with both treatments.
Difference is the time the treatment will take and that vaporising the
acid will need extra equipment. Trickling is faster and cheaper, same
result with less time and money spent...