We have been working with Bob Noel, a beekeeper in Cumberland, Maryland, since August, 1995.
In our opinion, Bob has discovered an effective and economical control for varroa mite (Varroa jacobsoni Oudemans (Acari: Varroidae)) and probably also for tracheal mite (Acarapis woodi (Rennie) (Acari: Tarsonemidae)); we saw very few tracheal mites in the hives examined.
The following is a brief account of our work and preliminary findings during the past year.
In summer and fall of 1995, Bob fed syrups containing essential oils1 to his bees, specifically wintergreen oil and spearmint oil. He mixed 10 to 20 drops (1/2 to 1 cc, respectively) of the oils to 453.6 grams (one pound) of sugar in a 0.95 liter (1 quart) jar, and hot water was added to fill the jar. This syrup was then fed to the bees at the entrance using a standard boardman feeder. He applied the two syrups to 14 hives as follows: spearmint oil to 5 colonies and wintergreen to 9 colonies beginning in July and continuing until October. In July, 1995, several of the colonies displayed typical PMS (parasitic mite syndrome): they were suffering from mite viruses, such as CBPV, from sacbrood which was quite heavy, and the brood pattern was scattered and incomplete, very similar to American foul brood (AFB), however, none of the colonies had AFB. Many of the emerging workers were small with shriveled wings and very small abdomens. Two of the colonies were so weak in July that wax moths were attacking comb and brood. Syrups were given ad lib and topped up daily. Bob assayed varroa mite populations by opening sealed brood cells, both drone and worker, by observing emerging brood and by directly observing varroa mite behavior.
Results: after using treated syrups for three weeks, Bob noticed improved brood patterns, healthier bees, and reduced mite populations. After 30 days of treatment (we inspected the colonies in August, 1995) varroa mites were definitely in decline and the bees were considerably recovered from PMS. On 21 September, we thoroughly inspected several hives; those that were treated with syrups were virtually free of varroa mite, whereas untreated control colonies in the area were heavily attacked by varroa mite, had typical PMS, and were beginning to die off.
In November 1995, Bob found that two of his bee yards (Oldtown, MD and Kifer, MD) which were free of varroa mites in July and August, were heavily infested with varroa mites (2-3 mites per adult bee). We believe that workers from collapsing feral colonies had joined with these colonies bringing in enormous numbers of varroa mites. Bob treated some colonies with apistan strips and grease patties (without essential oils) and others with grease patties containing the following: four cups of granulated sugar, two cups of shortening and 4.8 cc's of wintergreen oil. This mixture was made into 8 oz patties and placed one per colony above the cluster. The following spring and early summer only a trace of varroa mite could be found in the hives treated with the grease patties containing wintergreen oil; several of the colonies treated only with apistan and standard grease patties died out.
In May 1996, Bob devised the tracking strip method of varroa mite control: strips of 1/8 in. plexiglass, 7.5 cm by 35.5 cm (3" by 14"), were used as a support for a slurry made as follows: 4 parts mineral oil mixed with 1.5 parts melted beeswax; this liquid was then poured into 4 oz. baby food jars to which 2 cc's of patchouli oil and 2 cc's of wintergreen oil were added. Then ½ to 3 teaspoons of the slurry were applied to the each tracking strip with fingers, which were placed lengthwise just inside the front entrance of each colony. He began these treatments early in May. The day after strips were applied, dead varroa mites were found on the tracking strips--several dead mites per colony.
Bob's associate, Harry Mallow (a beekeeper for 30 years, former Maryland bee inspector, and former president of the Maryland State Beekeepers Association) treated one hive (his last surviving colony at beeyard No. 2) with the tracking strip on 31 May, 1996 (double the dose of patchouli and wintergreen oils; i.e., 4 cc of each oil in 4 ozs. of the slurry). On June 1st, both Harry and Bob observed several 100's of dead varroa mites at the entrance, on and around the strip. They returned on June 2nd to videotape the dead mites--most had been carried off by ants, but several dozen dead mites still remained at the entrance. Amrine inspected this colony on 6 June, 1996, and found very few live varroa mites on workers in the hive (two were seen on 1000's of bees examined). About 100 sealed drone cells were examined; several recently capped drone cells contained 18 to 25 highly aggitated varroa mites--they ran around the larva or pupa very rapidly and ran quickly onto and over the combs. It appears that at the time of treatment they entered nearly capped drone cells as if they were "bomb shelters" to avoid the tracking material. The older capped drone cells (with colored pupae and capped before the treatment) contained normal numbers of normally developing varroa mites.
On June 6, 1996, Amrine inspected 12 of Bob Noel's colonies, in three bee yards, and collected all varroa mites that could be found. About 100 sealed drone cells and several worker cells were opened in each colony. Four sealed drone cells were found infested with varroa at his "Rick's" bee yard in Cumberland, MD: two in colony number 4, treated with a tracking strip containing the mineral oil-beeswax slurry and 4 cc of patchouli oil in a baby food jar (4 oz); and one each in colonies 2 and 3 which were treated with the same slurry containing 2 cc of wintergreen oil and 2 cc of patchouli oil (in 4 oz.). Varroa mites were not found in hive number 1 (same treatment as hives 2 and 3). We regard these numbers as a trace infestation of varroa mites. (The same colonies were inspected by Maryland bee inspector Dave Thomas, who found no live varroa mites on 18 May, 1996). No deformed bees were found; there were 12 to 14 frames of brood in each colony which were the best looking colonies we have seen in the last three years.
Inspection of the Kifer, MD bee yard resulted in finding only two sealed drone cells with varroa mites (one each) out of 100 drone cells examined (hive number 3). This hive had been treated only with grease patty + wintergreen oil in November 1995, and a tracking strip (slurry made from 4 parts canola oil + 1.5 parts melted beeswax and 2 cc of patchouli oil) was added 30 May 1996. The colonies had two or three mites per adult bee in November, 1995.
Inspection of the Oldtown, MD, bee yard resulted in finding 3 sealed drone cells containing varroa mites out of 100 cells examined in each of two colonies. These had been treated with grease patties containing wintergreen oil in November 1995, and had received no other treatment. In November, the colonies had two or three varroa mites per adult bee.
Summary of Treatments:
1). Syrup: 10-20 drops of wintergreen or spearmint to one pound (453.6 grams)of sugar in a quart jar (0.95 liter); hot water added to fill jar.
2). Grease patties: made with four cups of granulated sugar, two cups of shortening and 4.8 cc's of wintergreen oil.
3). Tracking strips: strips of 1/8 in. plexiglass, 7.5 cm by 35.5 cm (3" by 14"), were used as a base for holding a treated slurry made as follows: 4 parts mineral oil mixed with 1.5 parts melted beeswax; this liquid was then poured into 4 oz. baby food jars to which 2 cc's of patchouli oil and 2 cc's of wintergreen oil were added. Then ½ to 3 teaspoons of the cooled slurry were applied to the tracking strip which was placed lengthwise just inside the front entrance of each colony. These treatments were repeated after 5 days: the old slurry, dead mites and dead deformed bees were scraped off and new slurry added.
Bob Noel's experiments from July 1995 to the present have demonstrated that essential oils in sugar syrup, grease patties and tracking strips are able to greatly reduce populations of varroa mites in bee colonies. 1) Spearmint oil at the rate of ½ to 1 cc per quart of syrup (1# of sugar) had the best results when fed in July through October; wintergreen oil was less effective, but still highly effective, in these experiments. 2) Grease patties containing 4.8 cc's of wintergreen oil were very effective from November until April in reducing and nearly eliminating varroa mites in heavily infested colonies treated in November. 3) Tracking strips containing 2cc of patchouli oil and 2 cc of wintergreen oil (or 4 cc of patchouli oil) are very effective in controlling varroa mites during spring build up. 4) In all cases of successful treatments, the essential oils were delivered to the brood nest of the treated colonies. The importance of this last observation can not be overemphasized. Two experiments of ours support the importance of this point.
First, Harry Mallow began sugar syrup treatment of 16 colonies at his bee yard No. 1 in September, 1995. He treated 8 colonies with syrup and essential oils only (4 with 15 drops of wintergreen oil per pound of sugar, and 4 with 15 drops of spearmint oil); the cans were placed at the top of the colonies (in contrast to boardman feeders placed at the entrance by Bob Noel). [Nurse bees and foragers collect nectar from a boardman feeder and the syrup and essential oils go to the brood; feeders at the top of a hive do not usually deliver syrups or food directly to the brood nest.] Four more of his colonies were given wintergreen syrup + apistan strips and the last four colonies were given untreated syrup as controls. Only the four colonies with wintergreen syrup + apistan survived. These colonies were treated too late and the syrup was fed in the wrong location: at the top of the colony instead of the entrance.
Second, Harry also treated one colony located in his beeyard No. 3 in April of 1996 with canola oil + wintergreen oil (4 cc of wintergreen in 4 ozs. of canola); a folded paper towel with canola + wintergreen was laid on a queen excluder above the cluster. He got a good kill of varroa mites (many were found dead on the bottom board). He continued this treatment for several weeks. We inspected the colony on 6 June, 1996: a paper towel with canola oil was on top of a queen excluder at the top of the colony (1 and ½ story); it had not been touched by the bees (in contrast, the original paper towel was shredded by the bees in April). [After April, the bees have little reason to go to the upper part of the hive and will not be affected by treatments placed there.] About 100 sealed brood cells (mostly drone) were examined in this colony; about 1/4 of the drone cells contained normally developing varroa mites. Obviously, this treatment, though effective in April when the cluster was near the top of the upper super, was no longer working. Thus the presence of the essential oils in the top of the hive was insufficient to cause reduction of varroa mite. This probably explains some of the negative reports we have read or heard from other researchers using essential oils--they apparently did not deliver the oils to the brood nest in a way that nurse bees and foraging bees would be treated; thus the tracking board at the entrance is highly effective, the syrup fed by boardman feeder is highly effective, and treated grease patties above the fall and winter cluster proved highly effective. The treatments must be delivered to the brood nest--in such a way that nurse bees and foraging bees are treated.
Proposed mechanisms of action:
Our observations of Bob Noel's experiments in 1995 and 1996 indicate the following mechanisms are probably at work in controlling varroa mites:
1) Direct toxicity: The grease patties and tracking strips indicate that the essential oils are able to kill varroa mites by direct contact, within 24 hours or less. Honey bees are not harmed by these oils at the rates used; honey has not been found to be contaminated by any of the treatments used to date (taste test). The evidence to date is strong enough to prove that this is definitely a mechanism of varroa mite control; however, no case has been observed where direct toxicity has totally elliminated the mites. For now, it can only be regarded as a partial control and effective only at time of treatment and for several days following.
2) Sensory disruption: it seems that the essential oils from grease patties and tracking strips are able to mask the normal chemosensory receptors on the tarsi and mouthparts of varroa mites, disrupting the mite's ability to function normally. As a result, they are not able to properly invade larval cells about to be capped, nor do they seem to be able to properly insert themselves under the sternites of worker bees and feed on bee hemolymph. They may not be able to recognize adults and mature larvae of honey bees because of the presence of the grease + oils on the mites' cuticle and sensory receptors. This mechanism is hypothetical and is supported indirectly by observations of behavior of varroa mites in treated colonies by Bob Noel, Harry Mallow and us.
3) Reproductive disruption: it is apparent that varroa mites in all three methods of treatments are not able to reproduce normally. Examination of cells at or near the time of emergence of bees and mites from mite-infested cells in treated colonies show that few newly developed females are found; many cells have been found containing dead immature mites and single females that never reproduced (so-called nonreproducing or sterile females). We conclude that the essential oils are able to disrupt the reproductive mechanism of the varroa mite.
It is known that under natural, untreated conditions, the female varroa mite, after feeding on a larva in a sealed cell for 1-2 days, normally becomes "gravid"--she appears swollen and the cuticular membrane between the sternal and genital plates becomes stretched and evident as white borders around the plates. The so-called "eggs" deposited by the female are in reality immature mites that are ready to emerge as protonymphs, the embryonic and larval stages having been completed within the chorion inside the body of the female. Thus, the female is converting the blood of the bee larva and/or pupa into nutrients for each developing immature mite. This part of the varroa's development is viewed by us as its weakest point, the so-called "Achilles' Heel" of the varroa mite, and appears to be the major target of action of the essential oils. The oils may be disrupting enzyme systems used to convert bee blood nutrients into nutrients for the developing immature mites and so the females are not able to produce "eggs". Also, after hatching, very few of the mites in treated colonies were able to complete development by the time the bee emerged from the cell.
These mechanisms help explain observations given to us by several beekeepers where honey bee colonies were located in regions with blooming plants rich with essential oils, such as mints, mellaleucas, eucalypts, etc., and which were often found to be free of, or not harmed by, varroa mites. We presume that the bees foraged on flowers of the plants, or on the resins of the plants for propolis, and returned to their colonies with these nectars or resins containing essential oils. Appartently, enough of the essential oils reached the brood cells so that the development of the varroa mites was disrupted in the colonies. This probably explains the failure of varroa mites to develop in many tropical regions, such as Brazil: the large variety of native flora apparently produce essential oils in nectar, pollen or propolis to the extent that normal reproduction of the mites is impaired.
We believe that these essential oils, which were originally produced by the host plants in order to kill, repel or prevent arthropod attack, are a very natural means of mite control. Honey bees are not affected by the essential oils, especially those from Lamiaceae (the mint family), because of concurrent evolution of the bees with these flowering plants and their essential oils; the bees long ago developed techniques to avoid, or counteract, the toxicity of the essential oils. However, the varroa mites, which were originally on Apis cerana in South and East Asia, apparently are susceptible to the essential oils. An important question is whether varroa mites will be able to evolve resistance to the essential oils; only time will tell. However, there are so many essential oils available, that if resistance to one appears, another oil may be substituted; the only real fear is whether varroa mite may eventually develop resistance to the entire class of essential oils.
Our future research will be directed toward 1) finding an essential oil treatment that will totally erradicate varroa mites from hives; 2) providing evidence to elucidate and document the mechanism(s) by which varroa mites are controlled by essential oils; 3) testing the oils at increased levels to determine toxicity levels to honey bees; 4) testing honey harvested from treated hives for the presence of essential oils.
We encourage other beekeepers to conduct research similar to ours in order to help find a way to eliminate bee mites. Please let us know if you have had similar results. Our interests in this project are strictly non-profit and for the benefit of the honey bee industry and beekeeping in general.
James W. Amrine, Jr., Terry A. Stasny, and Robert Skidmore
West Virginia University
P. S.: We can be reached at the following addresses:
Robert C. Noel, Teacher, Fort Hill High School
Computer Science and School Coordinator
108 Blackiston Ave.
Cumberland, MD 21502
Harry A. Mallow, Former Regional Bee Inspector, Allegheny & Garrett
Md. Dept of Agric. (under John Lindner)
11914 Valley Rd. NE
Cumberland, MD 21502
James W. Amrine, Jr.2 (Professor), Terry A. Stasny 2
(Research Acarologist) and Robert Skidmore
(Apiculture graduate student)
Division of Plant and Soil Sciences,
P. O. Box 6108, West Virginia University
Morgantown, WV 26505-6108
Telephone: 304-293-6023; E-mail: email@example.com
1 For a source of essential oils, we recommend Lorann Oils, 4518 Aurelius Road, P. O. Box 22009, Lansing, MI 48909-2009. Toll free number is 1-800-248-1302. Fax number is 517-882-0507. Lorann Oils will send catalogs to callers and will sell essential oils at wholesale prices to beekeepers (callers must identifiy themselves as beekeepers) in quantities from 1 oz. to 1 gallon. Beekeepers needing larger quantities should call for special pricing.
2Amrine has been teaching beekeeping at WVU since 1978, is past president of the Eastern Apiculture Society (1982) and is current president of the Morgantown Area Beekeepers Association; Stasny is founder of the Morgantown Area Beekeepers Association (1977), and has been a beekeeper for 30 years; Skidmore was a bee inspector for the Pennsylvania Dept. of Agriculture, Erie, Pennsylvania area in 1995.
Developed by Bob Noel, 24 July, 1996.
Make a stock solution that contains 2.5 ozs. of menthol crystals per half pint of vegetable oil (70.9 grams/236cc) or 5 ozs./pint (141.7 grams/473 cc ). (Menthol crystals are available from Lorann Oils at a competitive price; contact Lorann Oils at 1-800-248-1302 or 1-800-862-8620--identify yourself as a beekeeper and request a copy of their catalog. Address: 4518 Aurelius Road, P. O. Box 22009, Lansing, MI 48909-2009).
1. Weigh out and place the menthol crystals in a suitable jar, add the correct amount of vegetable oil (eg., Canola oil).
2. Place the jar in a pan of water on low heat until the crystals are dissolved (keep the lid on the jar).
3. For each pint of sugar syrup, use 1 teaspoonful of the menthol + oil stock solution. (Make syrup from equal parts of sugar and syrup; 1 rounded cup of sugar + 1 cup of water makes almost one pint of syrup).
4. After adding the menthol + oil, seal the jar of syrup until needed.
5. Make a sprinkling jar by punching holes in jar lid with a small nail.
6. When ready to treat for tracheal mite (Acarapis woodi), shake the sugar syrup well and pour into the sprinkling jar. Mixture should be warm--baby bottle warm.
7. Open the hive and sprinkle the full pint over the bees in the brood chambers. The bees will clean themselves and in the process, give themselves a dose of menthol which will kill the tracheal mites.
8. Repeat in 7 days to kill mites that hatched from eggs; or repeat as necessary.
9. Treatments in fall and spring are usually sufficient, but it can be used for a weak colony suspected of having tracheal mites. Be sure to treat swarms and new colonies: 2 times, five days apart.
10. If the menthol + oil crystallizes, reheat and crystals will dissolve.
Questions or comments please contact:
James W. Amrine, Jr.
Division of Plant and Soil Sciences,
P. O. Box 6108, West Virginia University
Morgantown, WV 26505-6108 USA