Formic acid fumigator for controlling varroa mites in honey bee hives
ABSTRACT The 50% formic acid fumigator (FAF) for varroa mite control was developed as part of a SARE grant (1999 to 2001). The fumigator was evaluated for five years on 123 colonies in five bee yards in Connecticut, Maryland and West Virginia. Treatments eliminated all mites on adult bees and 90 to 95% of mites in sealed brood cells. Very few brood or new young adult bees were injured by the treatment. The fumigator is a simple design and the overall cost of treatment is about $1.00 per hive or less. The 50% FAF was less toxic to bees compared to other treatments using 65%. 80% or 90 % formic acid (FA). The fumigator was applied for 18-24 hours, when ambient temperatures were between 10-30° C. In the USA, one treatment in mid-August to mid-September was effective and usually all that was required each year. The 50% FAF used with other essential oil treatments including salt-grease patties with wintergreen, feeding 1:1 syrup with Honey-B-Healthy7 (spearmint and lemongrass essential oils), and use of screened bottom boards together provide a synergistic effect to keep mite numbers at a relatively low level, as part of an integrated pest management (IPM) system.
- SourceAvailable from: Dennis VanEngelsdorp[Show abstract] [Hide abstract]
ABSTRACT: Controlling populations of varroa mites is crucial for the survival of the beekeeping industry. Many treatments exist, and all are designed to kill mites on adult bees. Because the majority of mites are found under capped brood, most treatments are designed to deliver active ingredients over an extended period to control mites on adult bees, as developing bees and mites emerge. In this study, a 17-h application of 50% formic acid effectively killed mites in capped worker brood and on adult bees without harming queens or uncapped brood. Neither acetic acid nor a combined treatment of formic and acetic acids applied to the West Virginia formic acid fumigator was as effective as formic acid alone in controlling varroa mites. In addition, none of the treatments tested in late summer had an effect on the late-season prevalence of deformed wing virus. The short-term formic acid treatment killed > 60% of varroa mites in capped worker brood; thus, it is a promising tool for beekeepers, especially when such treatments are necessary during the nectar flow.Journal of Economic Entomology 04/2008; 101(2):256-64. · 1.61 Impact Factor
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ABSTRACT: With the recent decline of honey bees, Apis mellifera (L.) (Hymenoptera: Apidae), there is a need for alternative or supplemental crop pollinators, such as Osmia cornifrons (Radoszkowski) (Hymenoptera: Megachilidae). However, O. cornifrons propagation could be impeded by a cleptoparasitic mite, Chaetodactylus krombeini Baker. We investigated the effects of formic acid and wintergreen oil on mortality of C. krombeini hypopi and O. cornifrons adults by determining the lethal concentration of each compound on each species. On average, >4.8 and >1.8 h were required to cause mortality in O. cornifrons adults when <2,473.5 ppm of formic acid and wintergreen oil was applied as a fumigant, respectively. When the two chemicals were directly applied to the exoskeleton of O. cornifrons adults, 353.4 ppm of wintergreen oil caused bee mortality within 10 min; however, no mortality was found with any formic acid application attempted. Mortality of C. krombeini hypopi occurred 5 and 10 min after application of >176.7 ppm of formic acid and wintergreen oil, respectively. Estimates of LC50 for C. krombeini hypopi treated with formic acid and wintergreen oil were 54.3 and 271.3 ppm, respectively. This study showed that C. krombeini could be controlled effectively without inducing O. cornifrons adult mortality based on concentration and duration of fumigation.Journal of Economic Entomology 12/2009; 102(6):2090-5. · 1.61 Impact Factor
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ABSTRACT: We used the 50% formic acid fumigator to treat 51 honey bee colonies in Florida on April 2, August 16 and October 23, 2006 and January 2, 2007, to control varroa mites. Treatments consisted of 90 to 110 ml of 50% formic acid mixed with 15 ml of Honey-B-Healthy™ essential oil concentrate to prevent queen losses. The fumigator was applied during daylight hours to each hive, screened bottoms were covered, openings taped over, and the entrance reduced to 3/8" by 3 1/2" (0.95 cm x 8.9 cm) and removed the next day after from 17 to 23.3 hours. Average mortality of varroa mites in capped drone cells was 93% (92.8% to 98.8%) (after adjustment for Abbott's correction for control mortality). Capped drone cells in old black comb had the lowest mortalities (66% to 84%): less of the 50% formic acid vapor was able to penetrate the thicker cappings.International Journal of Acarology 06/2007; 33(2):99-109. · 0.69 Impact Factor
FORMIC ACID FUMIGATOR FOR CONTROLLING HONEY BEE MITES IN BEE HIVES
James W. Amrine Jr.1 and Robert Noel2
1. Division of Plant and Soil Sciences, G-168 Agricultural Sciences Buildinng, West Virginia University, P.O. Box
6108, Morgantown, WV 26506-6108. USA (firstname.lastname@example.org); 2. Fort Hill High School, 108 Blackiston Avenue.
Cumberland, MD 21502, USA (email@example.com).
ABSTRACT - The 50% formic acid fumigator (FAF) for varroa mite control was developed as
part of a SARE grant (1999 to 2001). The fumigator was evaluated for five years on 123 colonies
in five bee yards in Connecticut, Maryland and West Virginia. Treatments eliminated all mites
on adult bees and 90 to 95% of mites in sealed brood cells. Very few brood or new young adult
bees were injured by the treatment. The fumigator is a simple design and the overall cost of
treatment is about $1.00 per hive or less. The 50% FAF was less toxic to bees compared to other
treatments using 65%. 80% or 90 % formic acid (FA). The fumigator was applied for 18-24
hours, when ambient temperatures were between 10-30? C. In the USA, one treatment in mid-
August to mid-September was effective and usually all that was required each year. The 50%
FAF used with other essential oil treatments including salt-grease patties with wintergreen,
feeding 1:1 syrup with Honey-B-Healthy7 (spearmint and lemongrass essential oils), and use of
screened bottom boards together provide a synergistic effect to keep mite numbers at a relatively
low level, as part of an integrated pest management (IPM) system.
Key Words: Formic Acid Fumigator, Varroa destructor, Acarapis woodi, essential oils, salt
grease patties, screened bottom boards, Apis mellifera, Honey Bee, Honey-B-Healthy7, IPM.
The varroa mite, Varroa destructor (Anderson and Trueman, 2000)(Mesostigmata:
Varroidae) and the tracheal mite, Acarapis woodi (Rennie, 1921) (Prostigmata: Tarsonemidae),
are the most damaging pests of the western honey bee, Apis mellifera L. (Hymenoptera: Apidae)
in the world today. Since their introduction to North America in 1984 (tracheal mite) and 1987
(varroa mite), virtually all wild colonies have been eliminated, and many beekeepers, both
hobbyists and professionals, have abandoned the profession. Those who remain have the hard
responsibility for maintaining healthy bee colonies for pollination of crops and for the general
welfare of the environment.
Organic acids and essential oils now play a bigger roll in integrated pest management of
parasitic mites and pathogens of honey bees, because of development of resistant mites and
pathogens. The Varroa mite has become resistant to synthetic acaricides (Pettis 2004). We
developed our four-fold treatment protocol (Amrine et al. 1996; Noel and Amrine, 1996) of: (1)
screened bottom boards, (2) wintergreen/salt grease patties (Sammataro et al., 1996; Sanford,
1995), (3) feeding essential oil concentrate, Honey-B-Healthy7 (HBH) (Noel 2006), and (4) the
50% formic acid fumigator (Amrine & Noel 2001), to reduce and control honey bee mites using
essentially natural ingredients. Five years of using the improved version of the formic acid
fumigator showed that only one or two, 24 hr treatments in mid-August to mid-September
(middle Atlantic States Climate) controlled both Varroa destructor and the less destructive
tracheal mite, Acarapis woodi.
For a full description of the other three protocols, please see our websites:
http://rnoel.50megs.com/2000/index.htm and http://www.wvu.edu/~agexten/varroa.
Abbreviations and acronyms used in this report: C - Centigrade, cm - centimeter, CT
- Connecticut, F - Fahrenheit, FA formic acid, FAF, formic acid fumigator, FA-HBH - formic
acid-Honey-B-Healthy7, FL - Florida, HBH - Honey-B-Healthy7, MD - Maryland, PMS -
parasitic mite syndrom, Qt - quart, WV - West Virginia, WVU - West Virginia University, “ -
MATERIALS AND METHODS
Screened bottom boards (using 1/8" (0.375 cm) hardware cloth) for varroa mite
control (Horn, 1987, Pettis & Shimanuki 1999) were used on all of our colonies. For our trials,
we made an opening in the back of the bottom board, below the screen, for inserting home-made
detector boards [12 1/4" x 16 7/8" (31.15x.9 cm) white demonstration board, coated with
petroleum jelly (Vaseline7)] which could be replaced with a sheet of masonite for fumigation.
Screened bottom boards take advantage of the natural, 10-20% mite fall that occurs throughout
the year. Without vaseline, the mites will crawl back up onto the bees.
The 50% formic acid fumigator, FAF, (Figs. 1-6) has two parts: an inner fumigator frame and an
outer supporting frame. The outer surface has the same dimensions as a Langstroth honey super
or 18" x 16 3" (45.72 x 41.275 cm). The inner fumigator frame (Fig 3) is 17 2@ long by 12 2@
wide (44.45 x 31.75 cm), made with :@ x 7/8@ (1.9 x 2.22 cm) wood molding (see details in
Figs. 4-5). The upper surface is covered with 1) standard aluminum or plastic window screen to
protect the absorbent pad from the bees on the underside, 2) an absorbent pad (non-woven
undergarment, Kendall7 7174 bed pads, available from hospital supply stores or drugstores) with
the absorbent surface down, and 3) a sheet of aluminum >flashing= (available from home
improvement stores) as a top cover, screwed into place with 4 screws, overlapping the two sides
of the fumigator frame by 2A (1.27 cm). This inner fumigator frame is nailed (from the ends)
into a 1 :@ x :@ (4.45 x 1.9 cm) outer supporting frame, with the same outer dimensions as a
Langstroth honey super (see above) forming two 3/8@ (0.9 cm) beeways on each side, with the
top, flashing surface of the inner fumigator recessed 3/8" (0.9 cm) below the top surface, and
with the bottom of the inner fumigator frame about 5/16@ (0.79 cm) above the bottom margin.
This construction provides an important air cavity, Athe activation cavity@ (Fig. 6), 1 3@ deep x
12 5/16@ x 17@ (3.175 x 31.27 x 43.18 cm), below the absorbent surface and just above the brood
frames. In American style hives, the tops of the brood frames are recessed about 3/16" (0.476
cm) below the super margin, and allowance for this additional space will have to be made in
British- or European-style hives.
Application - Before treatment, we taped over all holes, openings, etc., and we used a
solid bottom board, or sealed the bottom with an aluminum, plastic or masonite sheet. The
entrance was reduced to a small central opening 7/8" (.95cm) x 3.5" ( 8.9 cm) (Fig. 7).
At time of application (see below) we poured 2.9-3.4 ozs. (85-100 ml) of 50% formic
acid (depending on the size and number of the brood chamber(s)), mixed with 10-20% (0.5 to
0.67 ozs or 15 to 20 ml) of Honey-B-Healthy7 (mixed at time of application1) onto the pad and
placed the fumigator on top of the upper brood chamber, with the absorbent material down. The
amount of formic acid mix used depended on the number and depth of the brood chambers; eg.,
we used 2.9 ozs (85 ml) for a single deep chamber, 3.2 ozs (90 ml) for double Illinois chambers
or a deep + shallow, 3.21 ozs (95 ml), and for double deep chambers (3.38 ozs or 100 ml), etc.
Fumigation is done when the ambient temperature is between 17-31?C (60-85? F). The
fumigator is placed on the hive at about 12:00-18:00, and taken off at about 12 noon the next day
(18 -24 hrs. exposure). We kept detector boards on the hives for 13-14 days in order to sample
mite drop during one capped brood cycle (Fig. 8D, Fig. 9).
Summary of Application:
1. Ambient Temperature should be 60 to 90? F (15.5-32.2? C).
2. Apply treatment between 13:00 & 18:00 (1-6 PM), ideally mid-August to mid-September.
3. Manage all brood frames in one or two brood chambers.
4. Thoroughly mix 85 ml (2.9 oz) of 50% FA solution with 15 ml (1/2 oz) HB; pour onto
absorbent pad in fumigator. Place above upper brood chamber.
5. Tape all openings shut; if using screened bottom board, use solid Bottom Board or cover the
screen with masonite, plastic or aluminum sheet.
6. Reduce entrance to 3@ x 3/8@ (7.5 x 1cm) at center.
7. Remove fumigator the next day between 12:00 & 18:00
(noon and 6 PM).
In most cases, only one treatment is needed per season. We often go two seasons between
treatments, depending on # of infested brood cells (and # of incoming mites from dying and/or
After applying the FAF, the bees quickly began to fan the air through the brood nest and
out of the small bottom entrance; you could easily feel the air and smell the formic acid coming
out of the central entrance. During the treatments, average temperatures were 93-94?F (33.9-
34.4? C) between the full brood frames, 92-93?F (33.3-33.9? C) just below the fumigator at the
center of the hive, and the air exiting the entrance was nearly always 90?F (32.2?C).
Temperatures were lower in the weaker colonies with just a few frames of brood. We had
excellent mite kill on most hives in all of our preliminary trials (Table 1), including mites inside
sealed brood cells. Because of the addition of HBH, we saw very little interruption of queen
performance, and no balled queens in the WVU trial. In August, 2000 we conducted similar
trials with formic acid only (no HBH), at the same concentration and amount, and lost queens in
6 out of 24 (25%) colonies (Connecticut). The Cumberland, MD, preliminary trial (41 colonies),
at the same time and same doses of FA, but with HBH, had two queen losses or 4.3% loss, which
may have been due to failing queens. The WVU trial of 82 colonies in September 2000, using
the same doses of FA, but with HBH, resulted in no loss of queens. In 2001, in Cumberland,
MD, three queens in 46 (5%) FA-HBH treated colonies were lost. Another trial in Cumberland at
the same time, of 31 colonies using synthetic acaricides (Apistan & CheckMite) showed a 6%
queen loss (no HBH). We have used our 50% formic acid fumigator at WVU and Cumberland,
MD, for the past five years with the same, consistent results. In addition to adding the HBH to
the formic acid mix, spraying the bees and brood area with 1:1 sugar syrup with 20 ml of
HBH/Qt (0.95 l) helps to prevent queen loss.
Queen losses were reduced from 25% to about 5% or less with some trials showing 0%
losses, while obtaining a 90-95% kill of Varroa on the bees and in the cells in treatments lasting
less than twenty-four hours.
Some open brood, and hatching young bee losses could not be totally eliminated. This
minimal loss of a few hundred bees at most had no detrimental effect on colony strength
(40,000-60,000). The treatments stopped varroasis in thousands of brood cells and allowed brood
to hatch as healthy adults, free of deformities and disease. Large numbers of clean, healthy brood
are needed for a colony to successfully overwinter. The potential loss of a handful of bees is
minimal when compared to the thousands of bees saved by the treatment.
Table 1. Results of 50% FAF-HBH treatment of bee hives at WVU Horticulture Farm, 18 Sep 2000;
numbers of dead VM on sticky cards. Hives were maintained on two Illinois-style brood chambers,
with 7 frames of brood in each hive. HFH: Hort Farm Homestead; bees purchased from Weaver
Apiaries, Navasota, TX, May 2000. RNH-1: Robert Noel hive treated at the same time. All had been
treated with 4 weeks exposure to “low acid” by wicks into brood chamber from reservoir below hive
containing 40% FA and 10% acetic acid (had no effect on VM). We estimated an 80% reduction in
Hive # 24 hrs+3d
HFH-3 774 3804
HFH-5 1129 3024
HFH-8 1184 3039
RNH-1 544 540
By using a lower concentration of formic acid, approximately 44% after HBH is added,
we have reduced the chance of injury to bees.
This new, improved 50% Formic Acid Fumigator has inreased the efficiency of formic
acid in the following ways:
1) A recessed air space is provided just above the upper brood chamber within the fumigator.
Heated air from the brood rises into this enclosed space which has a controlled 92? F (33.3? C)
temperature. We call this space the Aactivation cavity.@
2) The upper surface of this space has an absorbent material saturated with a 44.1% FA-HBH
mix, overlying the entire brood area. The FA is much heavier than air (specific gravity of 1.11)
sinks to the bottom board and does not rise. This is probably why so many investigators had
variable results when placing small pads of FA on the bottom board, in the back corner of
colonies, in modified frames placed between brood cells, or in small pads on top of the brood
supers, but with no controlled heated or evaporation space and with a fully open entrance.
Placement of the FA-HBH mix about 1.25" (3.175 cm) above the upper brood frames is critical
for the performance of this fumigator.
3) By reducing the entrance to 3/8" x 3.5" (0.95cm x 8.9 cm)(Fig. 7), and by having only two
3/8" (0.9 cm)bee ways on the sides of the fumigator (Fig. 3), allows the FA-HBH mix to saturate
the hive atmosphere which then penetrates all capped brood cells, killing 90-95%+ of the mites
in most colonies in less than 24 hours. Dead mites can be found in brood cells during the next
13-14 days, and these accumulate in dense bands on the detector board during this time. (Fig.
4) The upper aluminum sheet prevents the warm air from being lost to upper supers (boxes of
frames for honey storage above brood chambers) (Fig. 2).
Thus, warm air rises from the brood and activates the FA-HBH in the absorbent pad
causing evaporation. The pad can hold 150 ml of solution without dripping. The bees respond
with a roar of fanning, and the FA-HBH saturated air circulates throughout the brood space and
eventually exits the small entrance opening. The circulating air is warm (90?F, 32.2? C) when it
exits; the FA penetrates capped cells, killing mites inside, but not the brood. Within 24 hrs,
virtually all of the FA has evaporated and the fumigator can be removed.
The more brood frames, the better the performance of the fumigator. We feed HBH to the
bees in August to stimulate brood production prior to fumigation with the FA.
The detector board should be left on for 13 days (14 days for drones) to get an estimate of
the mite population and mortality. This period corresponds to the number of days required for
one cycle of capped brood to complete development and exit cells. As bees exit the cells, dead
mites and debris fall between the frames, through the screened bottom, and onto the detector
board below. Some colonies produced counts exceeding 3,000 mites on a single detector board
in 13 days. We have 426 boards (Fig. 8B-E) taken from as many treatments, and it is very
satisfying to see the 1000's of dead mites in the petrolatum.
For most hives, one treatment usually places the colonies far below injury level for
several months (fewer than 5 of 100 examined drone cells infested). Occasionally, a second
treatment may be needed about two weeks after the first.
Honey-B-Healthy7 and Queen Preservation - Honey-B-Healthy7 is a mixture of
spearmint and lemongrass essential oils with water, lecithin and a trace of sodium laurel sulfate
to stabilize the product. It has a shelf-life of several years. It is formulated so that one teaspoon
(5 ml) of HBH delivers 0.5 ml of spearmint oil and 0.5 ml of lemongrass oil to the target
solution, which is usually a quart of 1:1 sugar: water syrup. We compared many essential oils in
treatments of colonies with parasitic mite syndrome (PMS) in 1995 and 1996; we found that
wintergreen and spearmint were excellent at reducing the PMS and allowing colonies to produce
normal healthy bees. Spearmint always gave superior results. However, honey bees are not
attracted to spearmint oil syrup; they may take a week to consume the spearmint syrup. Bob
Noel experimented with many additives to try to get the bees to feed on spearmint-syrup; he met
with success with lemongrass oil. The combination was excellent and the bees took it rapidly;
we timed a number of colonies that were eager to forage, and they often removed a single quart
in 4 hours. In cooler weather, or when the bees do not need to forage, the syrup lasts longer.
Essential oil components in Honey-B-Healthy7 modify the effect of Formic Acid (FA)
treatment on bee hives, such that queens are not lost. This aspect is extremely important for any
beekeepers using formic acid to treat varroa mites.
Fumigator evolution - In 1998-2000, we experimented with formic acid fumigation
using shallow honey supers containing absorbent cotton on an aluminum screen attached to the
bottoms; various concentrations of FA were placed on the cotton and the supers were placed on
the hives. In September-October 2000, the original, thin fumigator was developed which was
equivalent to just the inner frame described above, our 24-hour fumigation technique worked
extremely well for us in 60 - 70% of the hives treated. In 2001 we developed the present
fumigator with the larger above brood space and increased the efficacy to about 90% of colonies
treated. The present design has not changed since 2002.
Formic Acid Handling and Storage - Anyone repeating these treatments should
temporarily remove honey supers, wear rubber gloves, use eye protection and have water
available; do not inhale fumes (formic acid will enter the blood from the lungs and can be
harmful to the liver). The 50% formic acid was mixed ahead of time; it can be stored indefinitely
prior to use; but do not add the HBH until time of application. We always mixed the formic acid
and HBH in an open, outside area or in a fume hood, and we used a lowcost hydrometer ($5 at
www.williamsbrewing.com) to obtain exactly 50% FA (sp. grav. = 1.110). The hydrometer was
needed because we found considerable variation in strength of formic acid in containers that we
purchased; some were off as much as 30%. This may be one reason that published reports gave
variable results for the use of formic acid. Beekeepers must also be aware that formic acid
obtained from some commercial sources may contain heavy metal contaminants; these may be
harmful to the bees, to humans and to the environment. Always inquire about the possibility of
heavy metal contaminants. Keep the formic acid in a tightly sealed container and read the safety
label and the Material Safety Data Sheet (MSDS 2006). Store it in a cool, dry ventilated area
away from sources of heat or ignition. Protect against physical damage. Store away from direct
sunlight. It is strongly corrosive and should be kept in containers made of 316 stainless steel,
glass, ceramic or similar corrosion-resistant materials. Containers of formic acid may be
dangerous when empty since they may have product residues; always rinse empty containers
three times. Obsereve all warnings and precautions listed for formic acid (MSDS, 2006).
Cost - Formic acid is relatively cheap. Our supplier in Roanoke VA (Chemicals &
Solvents, Inc., 1140 Industry Ave., SE, Roanoke, VA; phone: 703-427-4000 ) sells FA in five
gallon containers for $51.67 (March 2006), which can be stored indefinitely. Purchased FA can
vary from 90% to 98% FA; when diluted to 50%, 5 gallons of FA would make about 9.7 gallons
of mix. Using it at 90 ml per hive, five gallons of FA would make up about 408 treatments. On
average, the cost of treating one hive is about US $1.00 or less after figuring in the cost of the
sugar syrup and the Honey-B-Healthy7.
Negative aspects of using formic acid - It is toxic and can cause skin and liver problems
if the operater is careless, especially with the concentrated acids (MSDS, 2006). However, the
advantages and simplicity of using FA certainly outweigh the disadvantages. It is found naturally
in honey in small amounts (Bogdanof et al., 2002). Beekeepers should remove honey supers
during treatments; they can be replaced the next day after the fumigator is removed. There is
occasional, minor brood injury and we noticed a small kill of young emerging workers and
emerging drones in 6 treatments conducted in April, 2005: about 25-100 bees per populous
colony. However, it is effective on tracheal mites as well as varroa mites, and no mite resistance
has so far been reported for Formic Acid treatments.
Why does the formic acid fumigator work? - The strong hydrogen bonds in formic acid cause
the vapors to act more like liquids than like gasses (Laffitte, 2006). Concentrated solutions of
formic acid, 60%, 65%, 80%, 85% and 90% (used in many different formic acid treatments in
Europe and North America (Anonymous, 2002; Becker, 1994; Imdorf et al., 1999; Chapleau,
2003)), act like liquids, not vapors when they evaporate. The dense vapors flow directly to the
bottom of the hive, and out onto the ground, where they kill grasses and weeds. When mixed
with water at 50%, the resultant vapor acts more like a gas, does not sink as quickly, and has a
longer ‘hang time’ in the brood nest. But it is still a fluid-like vapor that has the ability ot
penetrate the brood cappings and to kill the varrroa mites within the cells. Why does it kill
varroa mites and tracheal mites but not honey bees? Mites have cuticles more permeable to FA;
formic acid directly enters their hemolymph, acidifying the acarine brood, killing the mites.
Honey bees have a cement layer covering the epicuticle which repels many external chemicals
like FA. This cement layer is thinner and less effective in some larvae and newly emerged adult
bees which is why we see some mortality (100-500/colony) of small or recently eclosed larvae
and of newly eclosed workers and drones. The vast majority of the bees are not harmed by 50%
This fumigator is inexpensive, simple to use, and very effective if used on colonies with many
brood frames and when ambient temperatures are between 65-86? F (18-30? C). We believe that
State Departments of Agriculture and (USA) should make an exemption to apiary laws to allow
use of the 50% FAF to treat colonies infested with Varroa mites. We envision a central
beekeeper=s cooperative, regulated or licensed by the state, who purchases the concentrated
formic acid in 5 gallon or 15 gallon containers, diluting it accurately to 50% FA, and providing it
to beekeepers in small sturdy containers for treatment of their bees. Another effective way to
regulate the treatments would be for Beekeeping Clubs and Associations to function as a
cooperative as described above. They would buy the concentrated FA, dilute it accurately to
50%, and sell small containers of the solution to beekeepers needing the treatment. They could
even manufacture 10 or 20 of the fumigators and have them on hand to loan to the beekeepers.
Details of the construction of the fumigator are provided so that it can be made for a few
dollars, within a few hours, by anyone familiar with woodworking techniques. We want to make
this fumigator public knowledge in order to benefit beekeepers and the honey bee. The basic
fumigator and its concepts were presented in our research report to SARE (Amrine & Noel
2001), and thus deem its design to be public property. We have no intention of trying to obtain a
patent on this useful device. Infringement of this intellectual copyright property is prohibited
without proper acknowledgement given to the inventors of the device.
The once simple hobby of beekeeping is rapidly becoming the “science of beekeeping”
with knowledgable beekeepers who can find and identify pests, and know when and how to
apply various treatments to control them. Because varroa mite is now resistant to synthetic
acaricides, a disciplined, year-round treatment protocol will have to be followed, combining the
use of organic acids and essential oils, or similar techniques, to control parasitic mites and
pathogens in honey bees. Our united control efforts will vary by region, with adjustments made
for the various climatic conditions and beekeeping practices.
Finally, mites may not develop resistance to essential oils and formic acid as with
synthetic acaricides. Formic acid has been used in Europe for about 25 years with no known
report of mite resistance.
Caution - When working with formic acid, wear gloves, eye protectors and have plenty
of water available for flushing if needed. Remove honey supers before fumigation. Be sure to
have good ventilation or work out of doors. Do not allow the FA to become excessively warm
(eg, sitting in the sun) as this will shock the bees.
We encourage beekeepers to experiment with this fumigator and with various formic acid
formulations, in order to determine its efficacy and limitations. Please be careful and only work
with a few colonies at a time until we better understand its function under various conditions.
Planned Future Work - We intend to conduct trials in the future using the 50% FAF in
more tropical conditions, hopefully in FL, and if funding becomes available, in some other
This research would not have been possible without a grant from SARE, USDA, and support by
the West Virginia University Experiment Station. Robert Noel’s late sister, Marlene Noel, gave
him the idea, and valuable inspiration for using essential oils to improve the health of the honey
bee. Our colleague, Tony Delia, in West Redding Connecticut, provided much of the inspiration
for developing this formic acid fumigator. One of our greatest supporters for our mite research
over the years has been Vikram Prasad, M.D., West Bloomfield, Michigan. Many beekeeper
friends from throughout the US and Canada, and elsewhere have tried our fumigator and other
methods in our protocol and have given us positive results and many useful suggestions. Last,
but not least, we owe a great debt to our families for supporting us and putting up with out
frequent absences throughout the past 11 years. To all, we give our deepest thanks.
Published with the approval of the Director of the West Virginia Agricultural and
Forestry Experiment Station as Scientific Article Number 2952. This research was supported in
part with funds under the Hatch Act.
Figs. 1-6. Details of the 50% formic acid fumigator (FAF). - 1, FAF standing on edge; 2.
Top of FAF (Outside dimensions: 18" x 161/4" (45.72 x 41.275 cm)); 3. Bottom view of
FAF; 4. Side view details of FAF; 5. End view details of FAF; 6. The activation cavity
formed by the fumigator; evaporation of the 50% FA-HBH mixture is driven by heat from
Figs. 7, 8 - Details and results of formic acid fumigator (FAF) - 7. Entrance cleat reduced to
3.5" x 3/8" (8.9 x 0.95 cm) at the center; 8. Results of using the 50% FAF; A-C. Showing
initial treatment on 12 September 2000; D, E: Showing second treatment (13 days later) on
28 September 2000. (A. Test hive #5, MD, 12 September 2000 - honey left on to detect FA
contamination; B. Detector Board, ca. 500 dead mites. C. Close-up of B, 49 dead mites; D.
Same hive, 30 September 2000; E. Close-up of D showing 8 dead mites).
Fig. 9. Varroa mite development in drone and worker cells, showing period of capped cells
(modified from Martin (1997)).
Figs. 10-11. Demonstration of the 50% formic acid fumigator, 3-4 Apr 2006. 10. Monday, 3
April, 9:16 am, Church Bee Yard, Alachua Co., Florida. Arrow indicates the fumigator.
This is a one and a half story hive with just over 3 frames of brood. Fumigator was applied
at 9:15 with 85 ml 50% FA and 15 ml HBH. Clear sunny day, 88? F; in shade at 12:30. 11.
Same hive, 4 April 2006, 8:33 am (fumigator removed after 23 h, 18 m); some of the nearly
200 worker and drone larvae and pupae removed from capped brood cells; a total of 170
varroa mites were removed from worker and drone cells; all were dead except two in one
capped drone brood cell. An additional 69 mites were dead on the bottom board, which
were the mites on adult bees. Three, lively, small hive beetles (Aethina tumida
Murray)(Coleoptera: Nitidulidae) emerged from the hive and brood frames, unscathed by
the formic acid treatment. This was a demonstration conducted by Jim Amrine, David
Webb, FL beekeeper, and FL Apiary Inspector. A week later, the apiary inspector
reported that this colony was okay, bee losses were minimal, and that the queen was
present and laying eggs.
Amrine, J. W. Jr. and R. Noel. 2001. Controlling Honey Bee Mites with Essential Oils, Final
Report to SARE (Sustainable Agriculture Research and Extension, USDA), PROJECT NUMBER:
98LNE98-105 (usda 98-coop-1-5985), 28 Dec 2001. 11pp.
Amrine, J. W., Jr., Stasny, T. A., Skidmore, R. 1996. New mite controls investigated. Amer. Bee
Amrine, J. W. Jr., Noel, R. 2001. Controlling Honey Bee Mites with Essential Oils. Final Report to
SARE (Sustainable Agriculture Research and Extension, USDA), Project Number 98LNE98-105
(USDA 98-COOP-1-5985), 28 Dec 2001. 11pp.
Anonymous. 2002. Guideline on use of formic acid for Varroa control. Ministry of Agriculture
and Forestry Biosecurity Authority, Wellington, NZ. 11pp.
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