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Blane White
MN Dept of Agriculture
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>>> [log in to unmask] 04/02/02 07:49PM >>> wrote in part:
"You don't have to treat colonies for tracheal mite in the spring because the
queen bee
can lay enough brood that tracheal mite damage is not a problem.

Almost all bees that die of tracheal mite die in late December or January
because the
queen has NOT layed any new brood back in late October or November, and hence
all
these "old" bees are sick with tracheal mites.

Menthol KILLS tracheal mites extremely well IF IT IS INSTALLED IN VERY WARM
WEATHER which for Maine would probably be August 1st.  September would
definitely not be warm enough and menthol would not sublime into a gas that
kills the mites."

Sorry to disagree but Dr Basil Furgala clearly showed years ago that the time to treat tracheal mites here in the north at any rate is in the spring.  Colonies treated in the spring wintered fine while colonies treated in Sept here in MN died from tracheal mites in the winter.  The mite population is for some reason easier to control in the spring and treatment then results in very low mite numbers throught the next winter.  
Both formic acid and the menthol/oil treatment methods work well for tracheal mites but only formic acid treatment will reduce varroa mite levels in the hive as well.  Treatment time here in MN for tracheal mites is May.  Our main honey flow doesn't come until late June or more likely July.

FWIW

blane