from the apiguard web site
12. Q: It’s very hot where my hives are but the colonies need treating; is it safe to
use Apiguard in these conditions?
A: At temperatures above 25ºC (77ºF) it is possible to use a half-dose of
Apiguard and get a very good mite kill. Use 2 doses of 25g Apiguard, one week apart
instead of 2 x 50g at two weeks apart. A third 25g dose is sometimes used after the
second week where mite infestations are high.
When it is very hot, the thymol sublimes faster from the gel and the bees are more
active moving the Apiguard around. Both these factors increase the effectiveness of
the treatment and less product is needed. Make sure the hive entrance is not restricted,
allowing thymol vapour to escape.
randy oliver wrote an article on using apiguard in hot weather and also recommended a lower dose, you may wnat to look on his web site