The principle is called hyperthermi and two German devices for treating
frames of capped brood exist. These devices are called "Borgstaedter
Thermo Box" and "Apitherm" respectively. Varroa mites are less tolerant
to heat than the bees.
 
The interest of hyperthermi is low in Denmark due to poor results reported
(the brood is very sensitive to heating and the sensitivity varies with age
of brood.)
Some of my colleagues are currently experimenting with two different
ways of killing varroa mites by heating the entire bee folk. At a recent
meeting the two different principles was demonstrated.
 
The first one is designed for treating the entire colony including stores
and brood. In the end of the season you  place the brood chamber (the
entire box - or boxes) on a beetigth net of the bottom part of the device.
The bottom part consist of a shallow box with an opening the size of your
broodchamber. The top part is identical to the bottom. By means of
another box, the same higth as your brood chamber, a closed air circuit is
established through the brood chamber. Inside this box the heating (two
150w ligthbulbs) and a ventilator (like the one inside the computer in front
of You). The system  is controlled by a thermostat ensuring a temperature
of max. 44 degrees Celsius (11.2 deg F). The man that has build this
equipment is called Benny Bauer, he would be glad to hear from other
people with experience or ideas on the subject. He has no internet
access so please mail him at my address (below). Compared to the poor
results mentioned above (death of brood)he has few dead bees and
brood with his equipment. He thinks it is because the bees within the
closed circuit manages to keep a high moisture level. He has made
experiments this summer  and thinks he has killed lots of mites with no
harm to the bees. The treatment lasts about one hour.
 
The other device demonstrated at the meeting is meant for treating
swarms in summer or colonies in winter. You move the cluster to a net
cage. The net cage is placed in a vented oven at 49 degrees Celsius
(120.2 deg. F) for 15 min. Then the bees is put back into the hive. The
man that build this system claims that the low relative moisture content in
winter air combined with the heating is responsible for the death of the
varroa mites. Critics say that these bees will die from nosema afterwards.
The method should have been used for many years in Russia, but
literature is scarce -- references would be very much appreciated!
 
These methods are at current rather time consuming - at least compared
to just inserting Apistan strips- as I understand that Americans do. The
situation is different here in Denmark. We have had varroa in the country
since 1984, by now we have it all over, but still the only legal treatment at
present is formic- and lactic acid. All medication is also prohibited. These
working conditions cause us to give methods like above a second
thought.
 
Regards Morten
 
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