As far as oils and their success on overwintering this season, my guess
is that it was a bad winter to judge any treatment. Why? I had one hive
I gave up on last fall, so to prevent robbing and since there were so
few bees in the hive that they were going to die anyway, I closed the
entrance, tight. There were no ventilation holes and the only exit was
the notched inner cover- notch on top. No treatment, why waste it on a
soon to be dead hive. You know what's coming now. Yep. Doing fine. There
is still a handfull of bees and they are building up.
 
Everything was done wrong, in total violation of all I learned. Problem
is that the bees did not read the book. So I would not judge the effect
of oils or anything on the bees this winter. With varroa down, bees more
tolerant of tracheal mites and a "mild" winter about any treatment, or
in my case lack of it, would give good but totally incorrect results.
When varroa has a chance to come back and when we have a hard winter we
will have a better benchmark.
This was the first winter in Maine that I did not lose any hives. I used
the standard treatments of crisco and apistan. The only honey I
harvested after August was from supers over the inner cover, so the bees
had good summer honey to overwinter on. I think that is the best
treatment, because I lose my hives to dystentary first with mites
helping the weakened bees along. The buttoned up hive had summer honey
and no dysentary.