(To bee-L folks: in Canada we are quite close to having formic acid approved for
mite management in bee hives. We have 2 years of residue and efficacy trials
involving several thousand colony applications against tracheal mites, and will
be extending our experience to Varroa this year. After a year in the federal
approval process, the greatest concern has been with applicator hazard (include
bystander and hive inspector) for the liquid material (it is a strong acid which
will damage skin and eyes). Using gloves goggles and face shield, and a drench
gun for application, and requiring a 24 hour interval before inspection of the
colony, has allowed human exposure to be in the 2 ppm area, well below the
recognised industrial exposure limit (8 hour average) of 5 ppm. The "residue"
resulting from proposed tracheal mite applications (before or after honey supers
are in place) has been of no concern, never exceeding the levels naturally found
in some honeys, and returning to background levels well before harvest. Below
are proposed directions for use for Varroa control. I've extracted them from a
selection of European papers (brief results listed at the bottom). We don't
expect use against Varroa this season (not enough infested hives yet) but we
will be doing trials to refine the Varroa directions. We are also testing an
extended-release, low operator hazard formulation which we hope may supercede
the liquid.
 
I would appreciate comments (on the proposed directions, or other) from any of
you who have experience with Varroa and formic acid.
(note: the full label is much larger, with precautions about user safety and the
possibility of queen rejections (expect up to 10 %?, but we haven't seen any),
especially above 30oC. Below is just the use directions.)
 
PROPOSED
 Directions for use:
Use when outside temperatures are 10oC to 30oC. Leave hive entrances fully open.
In spring, complete treatments at least 14 days before the honey flow.
Do not use when honey supers are in place. Treatment may be applied in fall,
after the honey crop has been removed.
 
For a two-story colony (bees covering 8 to 20 Langstroth frames or equivalent):
For control of honey bee tracheal mites, apply 30 to 40 ml of 65 % formic acid
onto the bottom board, or on absorbent paper (three 15 cm square paper napkins
or paper towels) on the bottom board or hive top bars. Re-apply at 5 to 7 day
intervals, for a total of 3 treatments.
 
For control of Varroa mites, apply 20 to 40 ml of 65 % formic acid onto the
bottom board, or on absorbent paper on the bottom board. Re-apply at 1 to 4 day
intervals, for a total of 3 to 6 treatments.
 
For detection of Varroa mites, insert a sticky paper covered by a 3x3 mm mesh
screen into the bottom board, then apply 40 ml of 65 % formic acid on an
absorbent paper placed on the screen or on the hive top bars.  Check the sticky
surface for fallen mites after 24 hours, and again after 3 days, when it can be
removed.
 
For a one-story colony (bees covering 4 to 9 Langstroth frames or equivalent):
Apply half the amounts indicated above, using the same method and timing.
 
(end)
Here are the key European results used for the recommendations:
Fries, I. 1989. Short-term treatments with Formic acid for control of Varroa in
honey bee colonies in cold climates. Swed. J. Agric. Res. 19: 213-216
Seven treatment methods with Formic acid killed 61 to 97 % of Varroa over a 12
day period (demonstrates an acaricidal effect on Varroa in sealed brood). The
"normal" European recommendation of 85 % acid, 4 treatments  of 20 - 25 ml each
at 4 day intervals gave 61 % control (cf. 94 % Hoppe et al below), all others
were above 90 %, eg. 4 applications of 30 ml each, at 1 day intervals, gave
 97 %.  Queen losses of 5 % were recorded. (the proposed wording is consistent
with the better results, but avoids the 85 % concentration).
 
Lupo and Gerling 1990 A comparison between..formic acid and Taktic against
Varroa in beehives. Apidologie 21: 261 -267
8 applications of 25 ml, 85 % formic acid at 3 day intervals (21 day, 200 ml
total) gave control at least equivalent to amitraz smoke strips, in Israel in
June or August (98 % reduced in formic treated colonies). This is a much higher
treatment than Fries 89. (I used this info to increase the frequency
option in the proposed wording)
 
Hoppe et al 1989, and Bracey and Fischer 1989 (adjoining articles in ABJ Nov
1989 p 735 - 737, and 739-742. Hope et al: the most effective method used 20 to
40 ml (1 or 2 box hive, respectively), 65%, 4 applications at 4 day intervals on
the bottom board, and killed 94 % of Varroa. Bracey and Fischer used a 200 ml
reservoir (plastic tub) with a beer mat in a slot for a wick. They recommended 4
weeks of treatment during active brood rearing (total dose unknown) and got 99%
reduction in Varroa. Interestingly, with 70 % acid and temp from 28 to 40o C!!,
queen loss was nil.
 
I also have the instructions from Illertisser, Germany (pre-moistened absorbent
sheet pulp paper) and Meiers Sohne, Switzerland (user-moistened blotter as
above) both translated from German. My proposed wording is basically consistent
with their advice, except they say not to use the liquid in the hive, but let it
absorb well before the application; and to use in fall, not spring. (both
apparently not critical, from results above, and from our tracheal mite trials).
 
Again, I'd appreciate comments.
 
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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