Aaron wrote

>I believe the work was being done in Germany, and I may be
> incorrect that it has been abandoned.

We had a visit several years ago from a young lady beekeeper from Germany.
During our conversations, she told of research she had been involved with in
Germany on this heat question.  It seems that in the laboratory it was
successful with the varroa being able to be killed but the brood left alive.

However, the difference in temperature between killing the varroa and
killing the brood was not very much so that when it came to a field
situation, the field controls were not good enough to keep the correct
critical temperature.  It appears that a lot of brood was cooked in the
field.

Trevor Weatherhead
AUSTRALIA