The "Hygienic Factor" and Essential Oils

Vol. 13 No. 12 December 1997

The results of using essential oils in tracking materials during the brood season have shown varying degrees of effectiveness, which I believe is due to the differences in the hygienic behavior of the bees. Bees showing resistance to Varroa mites in different parts of the world may be due in part to the "Hygienic Factor", and impart to the essential oils gathered in nectar, pollen and propolis carried back to the hives by the bees. I classify my hives into three categories: super-hygienic, hygienic, and non-hygienic. I treated the colonies with three cotton pads layed across the brood frames; the pads were soaked with an eighty-five percent raw linseed oil/fifteen percent wintergreen mixture, 90 grams total. I had one super-hygienic hive that tracked up seventy-eight grams of oil treatment out of ninety grams placed in the hive in two weeks. In contrast to this, a non-hygienic hive of equal strength tracked up only twelve grams out of ninety grams on the three cotton pads in the same time period. After three months of treatment, Varroa mite populations were kept at ten percent or less infestation in drone cells in the super-hygienic hives (fewer drone cells in September). This showed a slight reduction in mite populations in the drone cells at the end of the three month study. The hygienic hives increased from 10% to 20% mite infestation in the drone cells (but with fewer drone cells at the end of the study); this shows the mites were held in check during this three month treatment. The mites propagated at normal rates in the non-hygienic hives: the mite infestation in the drone cells increased from ten percent to eighty percent in the three month treatment period in the non-hygienic hives. Three control hives two miles away also increased from 10% to 80% mite infestation in the drone cells. Out of the sixteen hives I had under this tracking experiment three were super-hygienic, five were hygienic, and eight were non-hygienic. The super-hygienic hives not only tracked up the oil but also had removed about 50% of the cotton pads every two weeks. The hygienic hives seemed to track-up the oil but were reluctant to tear apart the cotton pads. The non-hygienic hives avoided the pads and tracked up only a few grams of oil every two weeks. The super-hygienic and hygienic hives tracked the oil all over themselves and combs while the non-hygienic hives avoided the material as much as possible. Perhaps we need to focus on breeding a super-hygienic strain of bees and applying oil treatments to these hives for a consistent control. Terry Feaster, a beekeeper from Short Gap, West Virginia, had a hive with eighty percent Varroa mite infestation in the drone cells in July. He started the tracking pad treatment with the same raw linseed oil/wintergreen combination that I used. He treated weekly instead of every two weeks as I did with my experiment. A day after he applied the first treatment he found 84 mites on the stickyboard he placed on the bottom board. He then replaced the stickyboard with a new one and found 112 mites on it the following day. After forty-four days of treatment, the infestation in the drone cells dropped from eighty percent to thirty percent, with no mites visible on the bees as compared to before the treatment. This hive was hygienic. It tracked-up the oil but did not tear up the cotton pads. After the treatment it showed a decrease in mite populations. This one hive experiment does not prove a cure but may be a step in the right direction showing mite populations can be decreased during this critical time of the Varroa mite build-up period, using essential oils in tracking materials in hygienic hives. Next year we plan to increase the essential oil percentages in the carrier oils, to increase the frequency of doses and hope to find a better system of delivering the oils to both hygienic and non-hygienic hives. We need to find a tracking system to which the oils can be tracked all over the brood combs. Terry likes this treatment and believes that we can improve it next year. Terry has also been feeding and spraying his bees with wintergreen syrup for the past two years with continued success. Terry is an excellent beekeeper with an observant eye and analytical mind. I recently received a letter from an agricultural engineer from South America who fed eight hives internally with four different essential oils and had excellent results. They found that pennyroyal and wintergreen acted better than patchouli and spearmint. With no honey flow during the winter months, the only problem they encountered was robbing incited by the essential oil odor from the treated hives. They solved the problem by feeding in the evening. The critics have said the oils will contaminate honey, wax, and kill bees. If so, why do the bees go after the treatment so readily? Maybe it is because they are Natural Product! A beekeeper from Canada called and told me the dandelion bloom was in full bloom and he decided to fill empty combs with spearmint sugar syrup. As he did, the bees began to rob the combs and he had to stop the process. Reports of mites being resistant to Apistan may be in part due to this "Hygienic Factor": with non-hygienic hives avoiding the strips as they do the oil saturated cotton pads. Also, mixed reports of the efficacy of essential oils over the years may also be due in part to this "Hygienic" Factor. In contrast to this, all hives take the oils in the sugar syrup and deliver them to the brood nest where reproduction of the Varroa can be stopped during a dearth of nectar. Most hives are reluctant to take syrups and grease patties during honey flows. Several beekeepers have called and informed me that they fed their bees in late Winter and early Spring (February/March) and had excellent results with low mite counts and healthy bees throughout the honey flow months. These beekeepers fed primarily spearmint and wintergreen. Two of these beekeepers said their hives were in PMS and after thirty days of treatment the mites and the PMS cleared-up. Early Spring is an excellent time to feed the bees because they are building up and expanding their brood nest. With no honey flow and every cell in the brood nest being saturated with essential oils, the Varroa mites' reproduction can be stopped during this critical time of Varroa build-up. Feeding oils during honey flows causes the treatment to be diluted down to where it becomes non-effective. We have also observed that the stronger doses seem to prevent the adult Varroa from feeding on the pupae as well as preventing her from laying eggs. Very little, if any mite excreta was found in the cells of treated hives. These adult Varroa were very lethargic with some cells showing dead adult female mites. Keep in mind that the tracking systems drive the Varroa mites -- those that are not killed--off the bees into the brood cells during the brood season. But, if you feed syrups containing oils at this time, during a dearth of nectar, the safe haven of the capped cell becomes a sealed tomb for the adult female Varroa and her young. The oils placed in the food chain of the honey bee seem to stop the Varroa from reproducing. When you can stop the reproduction of a pest you may then possibly eradicate it. We need to find which oil, dose, or combination of oils will work the best in stopping the reproduction and killing every Varroa that enters a cell. Different lots of oil and the way they are processed seem to make a difference in solubility in sugar syrup. For some reason the oils mix better in honey than in sugar syrup. This may be because they are both natural. Many beekeepers call and ask about Tracheal mites. Before I began to use essential oils, I used regular grease patties and had good control of Tracheal mites in most hives. But due to which I believe is the "non-Hygienic Factor", or absense of the hygenic behavior, I had some losses to these mites. Last winter the few hives I lost were not to Tracheal mites. A commercial beekeeper from West Virginia called and told me that he had several non-hygienic hives that would not take the essential oil saturated grease patties or tear-up the paper towels he placed into the hives, but wintered well with only 6% total loss to his hives as compared to heavy losses to Tracheal mites prior to using essential oils. He felt that the fumes coming off the patties and the paper towels were enough to control these mites. He used a peppermint, wintergreen, canola oil, peanut oil and vegetable oil mixture in the paper towels. And a peppermint, wintergreen, shortning and granulated sugar mixture in the the grease patties. Back in 1919 in England wintergreen was used as a fumigant with some degree of success against tracheal mites. (R.O.B. Manley, 1946, Honey Farming, Reproduction, Northern Bee Books , West Yorkshire, April 1985, pp 256-267) Of all the different carrier oils, I have found that canola (rapeseed) and raw linseed (flaxseed) work the best for me in the tracking systems. I believe the reason for this is that they contain a high percentage of essential fatty acids, primarily oleic acid. Olive and peanut oil also contain a high percentage of oleic acid and have been found to be successful to some degree in mite control. Beekeepers call and ask about a protocol (plan of treatment) to follow using essential oils as they have for Apistan and menthol. It's going to be difficult to devise a plan that will meet the needs of all beekeepers in all areas. There are a lot of variables to consider, with the timing of treatment being most critical. Also, the "Hygienic Factor" will need to be considered. In areas in the far North with a short honey flow, feeding oils in syrup before and after the honey flow may work well and using essential oil saturated grease patties and paper towels during the winter months may be a good protocol to follow in this area. Areas in the South with continuous honey flows and year around brood production will make a plan of treatment more difficult. A combination of chemicals along with essential oils may have to be considered, especially with non-hygienic hives. I believe we have only scratched the surface on what these oils can do. They are anti-fungal, anti-bacterial, anti-parasitic, etc. It seems as though Nature's Chemist has provided in His pharmacy the essentials that we need. I caution beekeepers that a lot of variables need to be considered and data collected before we can claim a control. All we can do for now is let beekeepers know of our findings and hope that those that try the oils will let us know of their results. Anyone wanting additional information on essential oil treatments for honeybee mites can access Dr. Amrine's webpage at:

Bob Noel
108 Blackiston Ave.
Cumberland, Md 21502