Controlling Honeybee Mites with Essential Oils

Final Report for LNE98-105

Project Type: Research and Education
Funds awarded in 1998: $80,000.00
Projected End Date: 12/31/2001
Region: Northeast
State: West Virginia
Project Leader:
Jamie Amrine
West Virginia University
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Project Information


We developed a four-part protocol using essential oils (wintergreen, spearmint, and lemongrass) with screened bottom boards, grease patties, sugar syrup feeding, and formic acid fumigation to control honey bee mites. Protocol: I: modified screened bottom boards (1/8″ or 3.15mm screen). II: Feeding sugar syrup containing Honey-B-Healthy concentrate to stimulate bees. III. Wintergreen-salt grease patties to control tracheal mites and to reduce Varroa mites. IV. Formic Acid-HBH treated fumigator to kill both mites. Mite control with this protocol matches acaricide treatments without harming the bees, the beekeeper or contaminating bee products. The protocol has been disseminated to beekeeping clubs and individuals worldwide.

Project Objectives:

To control honey bee mites using essential oils in syrups fed to brood and in grease patties, slurries and towels or pads.

To identify the more effective essential oils and to develop and refine methods for the delivery of essential oils to honey bees in order to improve mite control and to reduce labor.

To determine if samples of honey and beeswax from treated colonies contain residues of essential oils and other chemicals used to control mites.

To disseminate information on controlling bee mites with essential oils to extension agents, beekeeping organizations, beekeepers, and other interested individuals.


Click linked name(s) to expand
  • Tony Delia
  • Tom McCutcheon
  • Bob Noel


Materials and methods:

We conducted experiments using the following methods, plus essential oils, to control varroa mites and tracheal mites (all methods are explained in detail and illustrated at Bob Noel’s web sites, Appendix 1):
I) Screened bottom boards: (1/8″ or 3.15 mm screen) with at least 3/4″ (1.9cm) of dead space under the screen. Dr. Helmut Horn in Germany made the original invention of the screened bottom board for varroa mite control in 1987. We made an opening in the back of the bottom board for inserting poster-boards for detecting mites (white demonstration board coated with petroleum jelly). This technique takes advantage of the natural 10-20% mite fall that occurs throughout the year. There must be some sticky material under the screen, or mites will crawl back up onto the bees; they are able to craw as high as 4 inches (10.2cm). Sand works well in place of sticky material–the mites die on sandy surfaces. Some beekeepers have nothing under the screens and the mites fall down into the grass where they can not get back up to the bees (Horn’s original design). When used with grease patties containing wintergreen, mite drop increases, approximately two-fold.

Considerably greater mite drop can be obtained by using paper towels soaked in canola oil or Crisco, to which 7% wintergreen or 25% menthol is added. We initially started with 15% wintergreen, which was too strong and caused some balling of queens and supersedures. When the essential oil-laced towels are placed on brood chambers, large numbers of mites drop off; by repeating the treatment in 10-14 days, most varroa mites can be removed from the colonies (90-95% reduction) and honey bee colonies saved. The timing of this treatment is best in August or early September.

II) Feeding Spearmint oil concentrate, Honey-B-Healthy. As a direct result of work connected with this grant, we developed a concentrate (Honey-B-Healthy or HBH) of essential oils and natural lecithin emulsifiers to add to sugar syrup; the emulsifiers allow even dispersal of the essential oils throughout the syrup. Many forms of lecithin were tried in order to find the most effective emulsifier; many methods for mixing the concentrate were tried until a good formula was found. The primary developers of HBH were Bob Noel, Atilla Kovacs and Tony Delia. It is made with lecithin, sodium lauryl sulfate, water, lemongrass oil, and spearmint oil. Two teaspoonfuls in a quart of 1:1 sugar syrup delivers a total of one cc of both essential oils (0.5 cc each); the essential oils are evenly distributed throughout the syrup. It took three years to develop this recipe for Honey-B-Healthy, which is sold to beekeepers throughout the eastern US. Careful quality control insures that every batch has the same quantities of essential oils and the same dispersal properties, while keeping the product at a reasonable cost.

We use HBH in early spring, fall and during periods when no nectar is available. HBH produces rapid buildup of bees and, in our opinion, helps to reduce pathogens. However, it does not kill adult mites. But, despite large numbers of mites on HBH-treated hives, there have been no deformed bees and no bee parasitic mite syndrome (BPMS). Control colonies with the same number of mites have many deformed bees, severely affected brood frames and BPMS. We believe that the spearmint oil, lemongrass oil or combination, inhibits development of viruses in the bees. It prevents mold and fungus build-up in 1:1 syrup solutions which can last for two or more years. We have observed that essential oil-laced larval food appears to disrupt the growth, reproduction, and mating of Varroa mites. We believe that others interpret this disruption in Varroa mite development as a false sign of mite resistance in honey bees. The essential oils in the syrup do not kill adult mites in the cells as does wintergreen and/or menthol in paper towels that kill or dislodge mites on adult bees. The action of the oils in the brood cells of the honey bee has yet to be determined. Similar observations by other researchers and beekeepers around the world may also be due to essential oil components collected by bees in pollen, propolis, and nectar. Due to variability in nectar flows and natural essential oils not being uniform, this observation is not always observed and may be difficult to repeat in field trials in the changeable, complex environments in which the honey bees live.

Our observations concerning our Italian strain of honey bees being “resistant” to mites over the past six years is that about 10% of our colonies have shown some degree of resistance to Varroa mites. We feel this resistance is actually due to hygienic behavior rather than real resistance to Varroa mites. We isolated these colonies and raised queens from them and found that most of the daughter queens (80 – 90%) lost the hygienic trait of their mother queen. As for resistance of the Russian queen, Albert Yoder compared mite infestation in his 20 Russian and 32 Italian hives and found mite levels to be about the same in both groups with one exception: the Russian strain did not display the signs of BPMS, as did the Italian hives. This strain of Russian queens that Albert tested seemed to have developed a resistance to the viruses transmitted by the mites, rather than to the mites. We consider this resistance to viruses to also be a false sign of mite resistance. The Russian strain has apparently survived with the Varroa mite for about 100 years in far eastern Russia: possibly the short growing season, possible essential oil compounds in nectars, pollen and propolis may have contributed to this strain’s survival. It seems that taking the Russian and Yugo bee out of their native environment has caused them to lose some if not all of their resistance in some trails, but not all. Europe has had the mites longer than the USA (since 1978, or 24 years), and they have yet to produce a truly mite-resistant bee. Research in mite-resistant honey bees should continue, but true resistance to mites may be a long time coming, if ever.

Research results and discussion:

A full discussion is integrated into the text under Impacts and Outcomes.

Participation Summary


Educational approach:

This grant involved the cooperation of the following individuals: Project Coordinator James W. Amrine, Jr., Professor of Entomology, West Virginia University, Morgantown, WV. Team Members: 1) Bob Noel, Teacher and Beekeeper, 108 Blackiston Ave., Cumberland, MD 21502; 2) Tony DeLia, Anpack Associates and Beekeeper, 51 Old Mail Coach Rd.,, W. Redding, CT 06896. 3) Tom McCutcheon, Roane County Extension Agent and Beekeeper, 200 Main St., Courthouse, 2nd Floor, Spencer, WV, 25276. Other key participants were: Harry Mallow, former MD Bee Inspector and Beekeeper, Cumberland, MD 21502; Atilla Kovacs, Chemist,, Frostburg, MD 21532; Albert Yoder, Amish Beekeeper, 11571 Arnold Rd., Orrville, Ohio, 44667; Monte Smith, Box 60, Beaver Lodge, Alberta, Canada, TOH-OCO; Melvin Peachy, 84 Willow Lane, Belleview, PA, 17004: Joe Kaveleski, Steubenville, Ohio, 43952, We also had considerable support from Mr. Joe Graham, editor, American Bee Journal, Dadant & Sons, Hamilton, IL. In addition, the following organizations assisted in conducting many experiments within the purview of this grant: Backyard Beekeepers, West Redding, Connecticut; Shenandoah Beekeepers, Harrisonburg, Virginia; NW Ohio Beekeepers, Lima, Ohio; Marion County Beekeepers, Marion Co. WV, Morgantown Area Beekeepers, Morgantown, WV; Allegheny Beekeepers, Oakland, MD; Cumberland Beekeepers, Cumberland, MD. Much of this information has been shared with beekeepers and beekeeping organizations throughout the US and Canada, and with beekeepers in Latin America, Europe, New Zealand and Asia. Bob Noel sent hundreds of letters to beekeepers describing our protocol worldwide. Jim Amrine sent hundreds of copies of the update file summarizing our findings by e-mail and regular mail.

Project Outcomes

Impacts of Results/Outcomes

HBH has several other very useful functions, as follows:

1) It helps to introduce queens: spray the brood frames and the queen cage with a mist of syrup containing HBH–the bees will immediately accept the queen with no chance of balling. We have not had any problems introducing queens since using this method. Albert Yoder showed that HBH was especially useful for introducing the Russian Queens.

2) HBH helps to reduce stings: mix a little on your hands and watch the difference in bee behavior–very few or no stings at all.

3) HBH prevents growth of yeast and fungus in sugar syrup: Amrine and Noel both have jars of syrup plus HBH (50% sugar, 50% water) over one year old which has not fermented, nor has the black fungus developed; this quality of HBH will be a boon for beekeepers who feed syrup to bees. We have found the same results with diluted honey: adding two teaspoonfuls of HBH per quart helps prevent fermentation and will prevent the black fungus from developing. We believe that fall feeding with HBH will enhance wintering qualities of bees; less honey will ferment in the hive, and fewer viruses will develop.

4) Probably the most useful benefit of HBH is modification of Formic Acid (FA) treatments on bee hives; we developed a 50% FA mix (see below) including 10% HBH, making a final mix of 44.1% formic acid, delivering 85ml of the mix to a typical hive. We got excellent mite kill on most hives, including mites inside sealed brood cells and because of the HBH, we had very little interruption of queen performance, and no balled queens in the WVU trials. In early August, 2000, we conducted similar trials with formic acid only (no HBH), at the same concentration and amounts, and lost 25% of our queens. The Redding, CT and Cumberland, MD trials resulted in two queen losses out of 41-colony treated, which was a 4.8% loss. This may have been due to failing queens. The WVU trial of 82 treated colonies resulted in a 0% loss of queens. A 46-colony trial in summer of 2001 in Cumberland, MD showed a 6% (3 queens) loss using the HBH-FA fumigator. Another trial at the same time of 31 colonies using synthetic acaricides (Apistan & CheckMite) showed a 9% queen loss. Some of these queen losses may have been due to late swarms not producing queens and to failed supersedures.

Apistan resistance appeared in the Cumberland, MD area in 2001. CheckMite continued to control mites in this area by beekeepers using it. A corroborator, Joe Kaveleski, from Steubenville, Ohio, used the HBH-FA fumigator on 10 colonies caging 5 of the queens and allowing 5 queens to roam normally, he lost one caged queen, which was above the treatment and may have been injured when handled. Another corroborator, Melvin Peachy, from Belleview, PA, applied 5 – 10 drops of lemongrass oil onto the top bars under the fumigator along with the HBH-FA mix in a seven-colony trial and lost no queens. Both beekeepers had an excellent one-day kill of Varroa using this system. This aspect of adding essential oils containing honey bee pheromone’s to the formic acid is extremely important for any beekeepers using formic acid to treat Varroa mites in honey bee colonies; it has long been a bane of formic acid that queen failure and poor queen performance can be expected as part of the treatment. Now, queen function can remain practically unimpaired with the use of HBH as an additive. Tony Delia made this discovery.

5) A side benefit for HBH: adding one or two teaspoons to syrup for hummingbird feeders keeps the syrup clean and attractive to the birds; again, the black fungus does not develop.

A major drawback for HBH revealed by our research, partly due to the design of the project, is that those colonies fed HBH were severely robbed by other colonies under conditions of drought and no nectar flow. The odor of the HBH is a powerful magnet for robbers, as well as for yellow jackets, bumblebees, bald-faced hornets and the European hornets (Vespa crabro). We compared plain sugar syrup with HBH-syrup to colonies on the same farms; although colonies were 1/4 mile apart, the robbing was still severe. Beekeepers need to feed all colonies with HBH or none of them during severe drought when no nectar is available. This was not a problem in the earlier part of the season. Beekeepers, when feeding HBH to all colonies in the fall will need to reduce entrances to keep yellow jackets and other bees and wasps from robbing the colonies. A collaborator from Argentina, Maria McDonald, seemed to have solved this problem by feeding in late evening: forager and robber bees quit flying, but the hive bees continue to consume the syrup.

Grease patties containing Wintergreen and Salt. Formula: 4 lbs [1.8 kg] of sugar, 1.5 lbs [.68 kg] of hydrogenated vegetable oil, 1/4 lb [.113 kg] of honey, and 1/4 lb [.113 kg] of salt, and 1.6 ozs. [45 cc] of natural wintergreen oil, one batch will treat about 8-10 hives, depending on number of brood chambers, size of patties, etc. The idea for using salt came to us from Monte Smith, Alberta, Canada. We placed 5 small patties (about 2 ozs. or 59.2g each) on top of each brood chamber and a ½” [1.27 cm] “roll” across the entrance, pushed about 3/4″ [1.9 cm] back in (rain will wash it away).

Adding salt to the patties doubles the rate of consumption by the bees; we used to change the patties monthly; with the addition of salt, the patties are often gone in 7-10 days. We believe the addition of salt enhances the effectiveness of the patties; the grease gets onto the bees and inhibits or kills the mites. Tracheal mites have not been a problem with any of our colonies that have grease patties on them. The wintergreen irritates the mites, making them turn more often and run more quickly and we believe they lose their grip on the bees and then fall through the bottom screen. We find that putting the grease patties on in June and leaving them on all year gives good reduction of mites, doubling or tripling the natural mite fall through the screened bottom boards, and prevents the mites from building up to such high levels. When the grease patties are used consistently, replaced every 2 weeks or so during the summer, with screened bottom boards, we see no tracheal mites and varroa mites seldom exceed infestation of 5 cells per 100– in colonies that consume the patties at a rapid rate. We keep the grease patties on all winter; they need to be checked monthly or so.

Different conditions in different geographic areas with different nectar flows and climate may affect the efficacy of grease patties alone with the screened bottom board. This is why we developed our HBH-FA fumigator: we believe it works consistently, independent of variables. Albert Yoder had a consistent two-year control for both tracheal and varroa mites using only the wintergreen/salt patties and the screened bottom boards in Orrville, Ohio in 2000 and 2001; no other treatment was needed. A drawback to using salt with the grease patties is that moisture is absorbed by the patties and salty water can often be found dripping down onto comb and onto the bottom board; using less salt and honey and more granulated sugar will reduce this problem. This is more of a problem in the fall when evenings and mornings are very damp with dew and condensation; it is less of a problem in July and August.

Formic Acid Treatments. This method of using formic acid to treat hives for control of varroa mites has not yet been approved in the United States. The only method currently approved is the use of a gel-pack that is slit on the top surface with a razor and placed into hives; a number of problems have developed with this method, including separation of the plastic packaging, queen loss, etc. If the above methods (1-3) are used during the season, there will probably never be a reason to use formic acid, Apistan (fluvalinate), or Checkmite (coumaphos). We developed three different versions of formic acid fumigators for treating hives with high mite numbers. Our current method consists of a 3/4” (1.9cm) recessed, 1.25” (3.2 cm) high wooden frame with 3/8” (0.95cm) bee escapes on each side to allow for slight ventilation and a bee way to the upper supers. A 1/8”(0.32cm) plastic screen (or aluminum window screen) forms the bottom, and a piece of heavy plastic or aluminum flashing forms the top. An absorbent pad (chuck or underpad) is placed in between, which holds and disperses the formic acid mix. Thus the fumigator is a sandwich of three layers, with the same x-y dimensions as a brood chamber. We poured 2.6 ozs. (75ml) of 50% formic acid, mixed with 10ml Honey-B-Healthy (mixed fresh each time: the HBH breaks down within 24 hrs and the solution becomes ineffective) onto the pad and placed it on top of the brood chamber, with the absorbent material down. The quantity of formic acid mix needed depends on the number and depth of the brood chambers. For example, we used 3 ozs (85ml) for a single deep chamber and for double Illinois chambers and slightly more (3.3ozs or 95ml) for a deep + shallow, or two deeps, etc. We manage the 80 WVU colonies in two intermediate depth brood chambers per hive, thus we used 85ml each. The fumigator was placed on the hive, on the upper brood chamber, for 24 hrs during warm to mild weather (19-30EC; 65-86EF.)–We reduced the entrance to 3.5″ (8.9 cm) at the center, and we taped or closed all other openings. Reducing the entrance is contrary to research published in Germany; but it makes our method using a lower 44.1% formic concentration much more effective. And, we replaced screened bottom boards with solid, airtight bottom boards and taped over all other openings. The bees immediately fanned the air through the brood nest and out of the small entrance. You could smell the formic acid coming out of the entrance. We measured the temperature of the air exiting the entrance and it was nearly always 90EF (32.2EC). We got excellent mite kill on most hives in September and early October, including mites inside sealed brood cells and because of the HBH we saw very little interruption of queen performance, and no balled queens. Our 400 detector boards indicated that mite kill was 90-95% in most hives treated. We conducted similar trials with formic acid only (no HBH) in early August, at the same concentration and amount, and lost several queens (25%) and had colonies stop brood rearing because the queen stopped laying (25%).

By using a lower concentration of formic acid, 44.1%, we reduced the chance for injury to beekeepers and to bees; however, frequent exposure to bare skin will cause the skin to come off. Any researchers attempting to repeat this experiment should wear rubber gloves. Those using formic acid should not inhale fumes, because formic acid can be harmful to the liver. We always made up the solution in an open, outside area or in a fume hood, and we used a hydrometer to obtain exactly 50% FA (sp. grav. = 1.110). Low-priced ($5), but accurate hydrometers can be obtained from We used a hydrometer because we found considerable variation in strength of formic acid in containers we purchased; some were off as much as 30%. This may be one reason that published reports give 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, or to the environment. Always inquire about the possibility of heavy metal contaminants.

We believe this new method of applying FA is effective for the following reasons: There is an air space just above the upper brood chamber: heat from the brood rises into this space. The upper plastic or aluminum sheet prevents the warm air from being lost to the upper supers. (We kept supers on during treatments in order to be able to test for FA in the honey above the fumigator). The FA (sp. grav. 1.22) is much heavier than air, so it sinks down from a container and does not rise. This is probably why so many investigators had variable results when placing pads of FA on the bottom board or between frames. To sum up: heat rises from the brood, activates the FA in the absorbent pad, causing evaporation. The bees respond with a roar of fanning, and the air circulates through the brood frames and eventually exits the small entrance opening. The circulated air is warm (90EF); the FA penetrates capped cells, killing mites inside, but not the brood. Within 24 hrs, virtually all FA is gone and the fumigator can be removed. We saw in all colonies, including 12 previously treated with Apistan, that mite drop occurred at a high daily rate for 13 days. Some colonies produced counts exceeding 3,000 mites on a single board in 13 days. This number of 13 days (14 days for drones) corresponds to the number of days required for capped brood to complete their 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, producing a banded pattern on the detector.

WVU had 35 colonies survive the winter; losses were mostly due to the severe drought last year when the only available “nectar” was syrup fed to bees, and to the granulation of Aster honey which was made in late September and October by the bees; it was too late in the year to feed HBH-syrup. Losses were also due to the late treatment of several hives with formic acid. We were developing the fumigator and conducting field trails in late August and early September, 2000, and thus the final version was not available until mid- to late September. Because the treatments were so late, some of the colonies were unable to produce sufficient healthy brood to survive the winter.

Bob Noel, in Cumberland, Md. lost five out of 59 colonies treated with the formic and HBH. He had an 8.4% colony loss compared to Maryland State losses of 50-70% for the winter of 2000 – 2001. We attribute his success to the timely treatments for mites and HBH feeding that helped preserve winter stores. Preventing spoiling and fermentation of winter honey stores helped reduce pathogen buildup and diseases such as dysentery. These preserved winter stores allow bees to go for longer periods of time during long winter cold spells before having to make cleansing flights.

We believe that we have developed an effective organic IPM for the control of bee mites, and for many of the pathogens they carry, using essential oils and organic acids. We see minimal, if any, contamination to honey bee products. All of the compounds we use in our IPM are on the EPA FIFFRA list, except formic acid. Formic acid being organic is already naturally found in honey in small amounts.

We were not able to assay the honey samples for essential oils or formic acid; we have the samples in a freezer and can analyze them if funding becomes available. We ran out of money due to the fact that a student assistant was paid from the grant when I thought she was paid by Work Study. Thus, several thousand dollars were taken from the grant for salaries without my knowledge. For further research we plan to fine-tuning our four-fold treatment IPM protocol.

Areas needing additional study

Much work has been done by many researchers to attempt to help save honey bees from the mites, but we have not seen until now a protocol or system that is as efficacious as our Four-Fold Protocol for managing honey bee mites using organic essential oils and acids. If we are unable to continue our work we hope some others will take our place and save “God’s Little Miracle Worker, His Precious Honey bee,” from possible extinction. Wouldn’t this be a lonely world without HER!!!

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.