(I was asked for some clarification of an article I wrote, on the loss
of queens (or at least peception by the colony, of a loss of the queen)
following application of formic acid for mite control. I'm responding
via the list, in hope of hearing from anyone who has experience with the
problem.)
(Background: Formic acid liquid is used in some areas, for killing
parasitic mites in honey bee colonies. Sometimes (rarely in my
experience) colonies which have been treated behave as if their queens
have dissappeared: building emergency queen cells. At that point, a
beekeeper would likely introduce a mated queen to keep the colony going.
Sometimes, when such queens were not available, the original queen
reappears. In other cases, the queen has apparently been killed by the
bees.)
I have reports of the following cases:
1) 10 queens reported lost out of 10, with the use of 85 % acid (as
opposed to the usual 65 % concentration),
2) 124 queens gone out of 220, using about 40 ml 65 % (field diluted
from 90 %) at about 90 deg F.
3) 60 queens gone out of 380, in single Langstroth hives, using 15 ml of
65 %, at 16 deg C.
4) a single hive which built emergency cells after treatment (30 ml x
65 % liquid on bottom board), but subsequently had the old queen still
laying.
5) several of about 10 hives (of about 20 treated) which did as in # 4
6) 153 of 480 2 box Langtroth colonies, built emergency cells after they
were treated May 20, 17 deg C. with 32 ml 65 %, on absorbent pads on the
top bars.
While cases 1 and 2 appear explainable by the concentration or
temperature, the others are not as easily explained. No these are not
controlled observations, with untreated control groups to indicate
whether the cells resulted from the treatment, but the presence of so
many synchronised emergency cells convinces most beekeepers who
experience it, that the effect is real.
The beekeeper reporting Case #3 suggested that the hives losing their
queens were (maybe) the stronger ones. Other cases, with less specific
losses (not counted) the beekeeper suggested the hives with older queens
were the ones most frequently affected. Another suggested it was mostly
queens from a specific queen breeder. Another speculated that the lost
queens were infested by tracheal mites.
The effect has been reported often enough to be a consideration in
formic acid use, but not enough to make it a high prioity to try to
reproduce and study, yet. I've been hoping that a pattern would emerge
in the beekeeper reports, that could then be confirmed experimentaly.
Kerry Clark, Apiculture Specialist
B.C. Ministry of Agriculture
1201 103 Ave
Dawson Creek B.C.
V1G 4J2 CANADA Tel (604) 784-2225 fax (604) 784-2299
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