The "Flash" Application Method for Formic Acid
by Jean-Pierre Chapleau
revised February 2010
Between Fall 2002 and Spring 2003, Quebec’s beekeepers witnessed a carnage
in their apiaries. Varroa was discovered as developing a resistance to
fluvalinate (Apistan). 50% of the colonies in the province were lost.
Many surviving colonies were weak and highly infested. What to do? A lot
of beekeepers saw formic acid as the best alternative.
Formic Acid: Cure or Killer? Formic acid is known to be efficient
against varroa. But how should it best be used? Presently in Canada, slow
diffusion methods are the standard. The formic is impregnated in different
support materials and then slowly released. Two commercial products are
commonly used :
Mite Wipe needs repeated applications - up to 6 times every 4 to 7 days
- depending on the level of infestation. Not quite the popular choice
for a busy beekeeper ! So it was no surprise when, last Spring, most of
them chose Mite Away. This situation gave rise to numerous problems.
- "Mite Wipe" a small pad containing 35 ml of acid, which will usually
evaporate within 4 days;
- "Mite Away" containing a super dose of 250 ml, which is released
The secret to an efficient and secure use of formic acid lies in adjusting
dosage to colony population, hive size, and also to temperature conditions.
Last Spring experience with Mite Away revealed the product was not well
adapted to weak colonies. In fact, damages were inversely proportional
to the strength of the colonies. What’s more, the use of formic acid is
not recommended in temperatures exceeding 26o C. Who is to
say there won’t be a hot spell during a treatment spreading over weeks?
This is precisely what happened last Spring when most regions of Quebec
were hit with 30o C. temperatures exactly during the treatment
period. Consequently, there were numerous losses of queens, brood and
even entire colonies! Therefore, my conclusion is Mite Away does not offer
the versatility required for a safe use of formic.
"Flash" application of formic from the bottom of the hive
In Europe, formic acid is given, not only by slow diffusion methods, but
often as rapid volatilisation. Let us call it : "flash" treatment. In
the early stages of the Varroa infestation in Canada, Kerry Clark, a former
researcher from British Columbia, tested and proposed the flash method.
But with the arrival of Mite Wipe and then Mite Away, it was put aside.
During a flash treatment, the acid concentration in the hive reaches a
high level which rapidly decreases after 6 hours. Such a level is even
said to kill some of mites in the brood. Usually the treatment is applied
as follows : A dose of formic acid is poured on a piece of paper towel
which has been placed either on the top bars or on the bottom board.
In our view, the flash treatment is interesting because it does permit
choosing the appropriate dosage for the situation. Being of such a short
duration, a flash treatment can be applied exactly when the right temperature
conditions prevail. So no more bad surprises with temperature!
However, another aspect seemed very interesting to me: the possibility
of not having to repeatedly open each hive by doing the application from
the sampling drawer of our specifically designed integrated pest management
bottom board (APINOVAR). Each of our hives rests on a screened bottom
board equipped with a sampling drawer opening from the side. Slide the
drawer half way open, throw in a paper towel, inject a dose of acid using
a drench gun (1), slide the drawer back in! And there
you have it!
I was using Mite Wipe before. These pads work well but the method is time
consuming. Opening and closing the hive many times implies the wax on
the inner covers and on the top bars has to be scraped out in order to
maintain a good seal, otherwise the formic vapours would escape the hive
from the top. Obviously the flash application from the bottom would save
tremendous time and effort.
We decided to run several trials. We tested flash both as a mid-season
treatment and as a fall treatment. A mid-season treatment can be needed
when August mite fall reaches dangerous levels. Treating colonies during
the summer requires first removing the honey supers. The problem is that
all the known treatments besides flash require several days, if not several
weeks. Who can afford loosing production?
Does the flash method stand up to the expectations?
As a mid-season treatment
As a mid-season treatment, the flash application gave a 60% reduction
of the natural daily mites fall. Meanwhile, the control group showed a
55% increase (2). All the colonies were doubles. They
received one single 40 ml dose of 65% formic. The application was made
at 20o C. This level of efficiency could be obtained because
the flash method effectively killed some varroas in the brood. We found
some dead varroas in brood cells we uncapped during the week following
the treatment. A careful examination of all the colonies showed no queen
or brood damage. A higher mites fall reduction (85-90%) was obtained with
another trial with a higher dosage (55 ml) at similar temperature. Nevertheless
this dosage is not recommended since 4 queens out of 30 were killed and
brood was damaged. A third trial with 55 ml at 13o C. revealed
completely safe for queens and brood.
60% reduction is sufficient for a mid-season treatment since the objective
is not to completely clean out the colony but rather permit it to safely
reach the Fall treatment period. Because of the short duration of the
treatment the test colonies were withdrawn from production for only 24
hours : Supers were removed during the day (normal crop removal); the
colonies were” flashed” at the end of the same day and new empty supers
were put back the next afternoon (3).
As a fall treatment
Flash was compared to several other Fall treatments. The trial involved
altogether 225 colonies in 4 groups:
Group 1: Flash (4 applications of 40 ml)
Group 2: Thymol only (4)
Group 3: 3 applications of 2 Mite Wipe plus one flash (40 ml) (5)
Group 4: 2 applications of 2 Mite Wipe plus one flash (40 ml) (5)
Almost all colonies were doubles. All were treated during the same period
(Sept 16 - Oct 12). For all treatments involving formic acid, a 65%
acid concentration was used, even if the Swiss Beekeeping Research Center
recommends 85% when applications are administered from the bottom of
the hive. The temperatures ranged from 15o C. to 24o
C. when the formic treatments were applied. Formic acid treatments were
applied at intervals of 4 to 7 days, except for the last flash when
it was decided to wait for good weather and more importantly for more
of the last brood to be hatched. Nevertheless, there was still some
brood in the colonies when the last flash application was done (6).
The flash group (group 1) had the best performance with a 92% reduction
of the natural mortality). The results of this group also showed the
smallest variations of efficiency. Only 14 colonies could be checked
for their queen and brood. They were all ok.
The thymol group had a lower efficiency. The natural mortality reduction
was only 70%. We feel that Thymol under our conditions, should not be
used as a Fall treatment unless the natural mite fall is low. Even then
a thymol treatment would be best followed by an application of formic
acid or eventually oxalic acid.
Group 3 (3 Mite Wipe and one flash) had an efficiency almost as good
as the flash group but with more variations between colonies. The average
reduction has been 90%.
Group 4 (2 Mite Wipe and one flash) had the lowest efficiency: 66% reduction
of the natural mortality.
It is important to mention that the
goal of these Fall trials was not to rate the absolute effectiveness
of these treatment options but rather to compare flash to several other
treatment options in the same conditions.
Flash was also experimented on singles as a Fall treatment. The efficiency
was higher. With only 3 applications we obtained a 96% reduction of
the natural mites fall. This can probably be explained by the fact that
colonies in singles stop feeding brood earlier. There was no more brood
when the last flash treatment application was done in mid-October. As
a matter of fact, for this reason, varroa control is much easier with
colonies in singles.
In 2004 a standard Coumaphos® treatments was compared to 4 flash
applications. Half of the colonies in each group were singles, half
were doubles. The table and graph below show the results that were obtained:
2004 comparison of flash(4) with
All the queens were checked
in the Flash group at the end of the treatment. All were ok.
Dosage-temperature combinations we used:
These charts summarize the different dosage-temperature combinations
that we used each year. In 2004 the flash was experimented with success
at higher temperatures. All these combinations were found to be safe.
A test with with
50 ml at 22-24o C. on doubles in August resulted in some
queens stopping laying for several days (>5%). Another queen had
The configuration and size of our IPM
board entrance differ from a standard bottom board (7).
This may influence the distribution and retention of the formic vapours
in the hive. We have not checked if the same efficiency is obtained
with other types of bottom board with these combinations of dosage and
The following table summarizes all the trials involving flash that we
conducted in 2003.
mite fall before
mite fall 14 days after
55 ml doubles
27 ml singles
(once or twice at 7 days interval)
end of day
119 (1 treatment group)
148 (2 treatments group)
10 (1 treatment group))
22 (2 treatments group)
85% (1 treatment)
91% (2 treatments)
4 queens lost for 30 applications; some brood killed; interruption
in egg laying;
40 ml doubles
20 ml singles
200°C end of the day
10 flash plus 14 untreated controls
116 (flash group)
52 (control group)
48 (flash group)
71 (control group)
59% reduction for flash group and a 55% increase
for the control group
no queen loss; no significant brood damage; no interruption
in egg laying
50 ml doubles
25 ml singles
no queen loss, no brood damage, no interruption in egg laying
(21 colonies inspected)
16 to Oct. 12
40 ml doubles
20 ml singles
during the day (4 successive treatments)
65 strong colonies almost all doubles
92% reduction of mites fall
14 colonies inspected after first application : no queen
loss, no brood damage
50 ml doubles
variations during the day : (10 to 2°C)
60% of varroas on adult bees killed after a Coumaphos®
check (57% et 63%)
queens OK and brood OK
24 to Oct. 12
colonies in singles
96% reduction of mites fall
queens not checked
Conclusion and discussion
In our trials the flash method showed interesting potential as a Fall
treatment in replacement of chemical treatments.
In 2003, given the very high level of infestation
at the outset of the treatment period, none of the alternatives tested
reduced the natural mites fall to a save level for the Winter (9)
but the flash method, with 4 applications, gave the best results. In
2004 the the mites fall reduction by the flash method has been more
important, reaching 96,2% compared to 98% for the Coumaphos®. Theoretically
with average daily natural mortality levels that would be around 25
before the treatment, a 96% reduction would result in a natural mortality
under 1 varroa/day after 4 applications.
Flash also seems to be a good mid-season treatment because of both its
extremely short duration and good efficiency as a single application.
A mid-season flash application can release the treatment pressure in
September and the number of treatments required. It is a useful tool
in a IPM strategy.
The flash proved to be the fastest treatment to apply. I takes 10-15
minutes for a person alone to treat a 28 hives yard. It was also very
economical. It cost approximately 0.32$ per colony for a full Fall treatment.
Flash treatment method is a versatile and economical approach. Considering
our results so far, we are already planning to use it from now on as
our main method of treatment for the end of the season. 2003 was the
first year we did not use Apistan. I felt reassured by these results.
I am now convinced that non chemical IPM is not only possible, it is
Flash would need to be tested in a wider range of circumstances and
further trials are necessary to further optimize the dosages we have
Flash should also be experimented during Spring. We found that small
or medium size colonies are affected in their development when they
are continuously exposed to formic vapours for a long period. We suspect
this side effect could probably be avoided with flash. If you consider
doing some tests, it is important to remember that damage to colonies
can occur if unsafe dosage-temperature combinations are used. It is
important to repeat that weak colonies could find it difficult to put
up with the dosages found to be secure at the end of the season for
normal colonies. Based on our findings as well as on European literature
on the subject, for a first Spring trial, the dosage at 20oc should
not exceed 2 ml per frame of bees (8). Again, this
experiment should at first be conducted with a small number of colonies.
We could not evaluate the efficiency of flash against tracheal mites
as we do not have tracheal mites.
A very quick test also confirmed the possibility of using 85% formic
at temperatures around 10. We can look forward to a still greater efficiency
when colonies are broodless in October. The possibility of using oxalic
in November as a complementary treatment, like it is done in Switzerland
and other European countries, is also very promising. We tried that
combination and we will be reporting on that on our web site.
We hear that the use of formic may soon be illegal or only authorized
through restricted approved methods, if not a single one. It would be
imperative that the use of the flash method of application be made legal
as all other good methods. While the chemical solutions are getting
exhausted, the beekeepers need a good toolbox to be able to build efficient
Internet links on the subject:
Instructions pour l’utilisation ponctuelle de l’acide formique
Centre suisse de recherches apicoles
Short Term Treatment with Formic Acid
Guideline on Use of Formic Acid for Varroa Control
Ministère de l’agriculture de la Nouvelle Zélande
Other suggested reading:
Imdorf, Anton, Stratégie
de lutte alternative contre Varroa destructor en Europe centrale
(2003), in Colloque
en apiculture, La lutte intégrée contre les parasitoses
de l'abeille, Centre de référence en agriculture
et agroalimentaire du Québec (vx 002)
- We used NJ Philips drench guns (20 and 30 ml models).
They should be cleaned and lubricated after each use according to
- Natural mortality was evaluated the day before the
treatment and then two weeks after leaving time for the brood, that
had been sealed at the time of application, to hatch.
- We could not submit the fall honey from these colonies
to a residue analysis. PMRA's "note to CAPCO" on formic
acid suggests waiting 2 weeks after a formic application before honey
supers are put on. It has to be mentioned that this note was a proposal
to schedule formic acid, but that formic was finally never "scheduled".
Any use of formic to treat colonies presently falls into a "gray
zone" and clarifications are expected by the beekeeping industry.
- The product used was Thymovar®. It has been
used according to the manufacturer’s specification for a period of
- A fourth application of Mite Wipe had been initially
planned for this group it had to was replaced by a flash treatment.
The reason for this change was to be able to complete the last application
of formic for all hives within the small window of mild weather offered
by nature at that time.
- The remaining brood at that moment can be evaluated
at 2 or 3 frames on average (more or less 600 sq. cm).
- The APINOVAR board we
used has an entrance 1 cm x 37 cm, i.e. half the size of a normal
- This is the dosage
we suggest with APINOVAR bottom boards.
- Recommandations formulated by the "Centre
suisse de recherches apicoles" suggest 30 as a maximum daily
natural mortality level just before the Fall treatment is started.
It is also suggested that the natural mortality level should be reduced
to ½ varroa daily before the winter.