Hello Jean-Pierre
 
   I've consulted with a few researchers from Europe with experience over
   several years, with formic acid treatments. Dr. Ingemar Fries from
   Sweden has been very helpful. As I've said, the queen rejection problem
   hasn't been enough to measure in the trials (about 500 colonies over 4
   years) or in the cooperating operation I work with (1700 hives treated
   over 3 years).
 
   A good answer to your question about how much queen rejection to expect
   from formic acid treatment, would start with a discussion about the
   details of the treatment regime. Different frequencies, and especially
   dose size and concentration, can be used to get effective control of
   several mite species.
 
   Ingemar says  5 % queen loss from 4 treatments with a commercial source
   of pre-moistened blotter material, which is labelled as having "14.2 g
   waterfree formic acid", is a typical expectation. (Since waterfree
   formic is very expensive, I imagine the plates actually contain some
   standard dilution ( 85 % perhaps) with the equivalent of the labelled
   amount. His 1989 paper, "Short Interval Treatments with formic acid for
   control of varroa .. in cold climates", had 5 of 91 queens lost (all
   after the first treatment, 3 were found dead), with that sort of
   treatment. He says losses of queens are avoided with the extended or
   prolonged-release plates (Kramer).
 
   Two other cases from Canada I could mention: ( 30-40 ml 65% liquid
   applied on absorbent paper on top bars)
   10 of 30 queens were lost when hives were split in the middle of a 14
   day treatment period. The queens  lost were some of the ones being
   introduced in cages. Not surprising.
 
   In a small group of treated hives, 1 queen (marked) was found on the
   bottom board the day after the first treatment. It was found that there
   had been 2 queens in the colony.
 
   Generally it sounds not serious, but it's worth finding out how to avoid
   things like the case of 150 queens lost of 500.
 
   regards
 
   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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