If I recall, the first posting about Oxalic Acid said some (or all)the
the wintered bees died of nosema. If it was not nosema but dysentery
(which also kills), that would fit in with "acid" sugars effect on bees.
Tartaric acid and acid treated HFCS causes dysentery which is not
noticable on spring and summer fed bees because they void or die outside
the hive, and the ones that die are not as apparent during buildup. So
you could get great results (varroa kill wihout seeing the effect on the
bees) during the spring and summer but have winter deaths by the acid
treated sugar. Just check with the beekeepers who fed their overwintered
hives with acid treated HFCS and saw all their bees die before charging
off with oxalic acid for winter feeding.
Then again, it really may have been nosema and the silver bullet is
truly here. But until the reasons for the winter kills are sorted out, I
will use Apistan.