[log in to unmask] asks about the effect of increased temperature on
Varroa.  It has long been known that increased temperatures in a hive will
kill varroa before it will kill the bees.  This raised temperature can be an
effective varroa control.  The problem is that the lethal temperatures for
mites and bees are very close (within a few degrees) and it is very hard to
control the temperature to achieve effective mite control without killing
the hive.  It's usually a case of, "The treatment cured the malady,
unfortunately it killed the patient!"  Remember also that while the
beekeeper is trying to raise the hive temperature to kill varroa the bees
are trying to cool the hive because that's what bees do.  Raising
temperature is also not  a practice that lends itself to a lot of hives.
The practice was abandoned as effective but impractical early on in the
varroa crusades.

As far as sunny hives having low mite loads while shady hives do not, I
doubt there's much to a temperature parameter in your observations.  The
mean hive temperature will be constant as the bees thernoregulate.  The
sunny bees will work to cool their hives, the shady bees will work to warm
their hives.  However, there can be large variations in mite loads across
different micro-climates.  If you've noticed a difference in your two
locations, you might consider moving the hives with the heavy loads to the
same location as those with lesser loads.

Aaron Morris - I think, therefore I bee!