Controlling Honeybee Mites with Essential Oils

1998 Annual 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

Controlling Honeybee Mites with Essential Oils


This project is evaluating and improving the use of commercially available essential oils to control honeybee mites. The scope of work includes refining present approaches to develop better application methods, determining optimum time of delivery, and identifying more effective essential oils. We will compare the health and productivity of untreated colonies, colonies treated with Apistan alone, and colonies treated with essential oils. We will analyze samples of honey and beeswax from treated and control colonies to determine the presence of residues of Apistan and essential oils in the honey and beeswax.
The following report covers the first year’s activities.

1.Control honey bee mites using essential oils in syrups fed to brood and grease patties, slurries and towels or pads.
2.Identify the more effective essential oils and to develop and refine methods for delivery of essential oils to honey bees in order to improve mite control and to reduce labor.
3.Determine if samples of honey and beeswax from treated colonies contain residues of essential oils and other chemicals used to control mites.
4.Disseminate information on controlling bee mites with essential oils to Extension Agents, Beekeeping Organizations, Beekeepers and other interested individuals.

Early in our experiments, we were unable to evenly mix essential oils into sugar syrups: oils gathered at the top of solutions, and then killed the bees when containers were emptied. Bob Noel, Attila Kovacs, and Tony Delila developed a spearmint oil-lemon grass oil concentrate by using a specific type of lecithin (over 20 types were tried), heat and careful mixing of the essential oils. By adding two teaspoonfuls of concentrate to each quart of sugar syrup, we obtain a mix of 1 cc of each essential oil into each quart of syrup, and the essential oils stay in uniform suspension throughout the syrup and throughout the treatment. The essential oils will not separate, even after several days. Samples are available to interested beekeepers.
We found, in 1998-1999, that lemongrass oil is an excellent feeding stimulant for honey bees. Solutions of sugar syrup containing spearmint oil or other strong oils tend to be ignored by the bees; however, adding an equal amount of lemongrass oil to the syrup results in rapid consumption. We observed several colonies take 1 QT of syrup in 4 hours, which is very fast feeding. The consumption of the lemongrass oil also stimulates egg laying and larval development, so that treated colonies develop more rapidly than do those receiving only sugar syrup.
In 1998, WVU obtained 35 colonies (many by donation); we spent the summer spreading mites into the colonies until about 15 percent of all brood cells had mites. We used these colonies in trials starting 14 Aug to 1 Oct, 1998. Bees were fed syrups containing essential oils: wintergreen, lemongrass and spearmint. Results: the honey flow was excessive and it diluted essential oils to the point that no reduction of mites was observed. We learned that feeding syrups containing essential oils to bees for mite control must be done during a dearth situation: i. e., when no, or only small amounts of nectar are coming in. Bob Noel fed concentrate-diluted spearmint-lemongrass syrup to several colonies with mites in late February, March and April, 1999: he fed as much syrup as bees would take (3-4 gallons total per hive). Examination of colonies in May and June showed that very few varroa mites survived the treatment: less than 4% of brood cells had mites.
During winter 1998-1999, WVU lost all but 12 colonies due to mites (Bob Noel lost only 2 of 54 colonies: but, he was not trying to maintain mites). In winter and spring, 1999, we purchased and assembled equipment, bought 45 packages and divided colonies, building the WVU apiary up to 60 colonies. We then spent most of the summer spreading mites to colonies in order to have sufficient populations for tests (15 percent of brood cells with mites present).
We began treatments on 19 Aug., 1999. We divided colonies (with sufficient mites) into groups of 5 colonies for controls. Overall, we found that using grease patties during the winter months, followed by early spring essential oil feeding, eliminates the need for spring chemical treatments, and results in strong healthy hives for spring pollination and summer honey flows. Bob Noel sees almost no noticeable mite infestation until late summer of fall.
In order to find a way to reduce mites in severely infested hives, in August, 1999, Bob Noel replaced mineral oil + wintergreen in ‘wick hives’ with two organic acids: 18 percent formic plus 5 percent acetic. This solution was placed in the reservoirs of wick hives as described above, and was left on the colonies for one week. Modified detection trays (which slide out from rear of hive; they are covered at the top with 1/8 inch hardware cloth, as in pollen traps), allowed us to see mite drop occurring before and after the treatments were applied. We found that we had to reduce colonies to a single brood chamber. we covered the brood chamber with an inner cover, and taped the central opening so that only a small space was available for bees to go up. We placed a queen excluder above the inner cover to keep the queen in the brood chamber.
The organic acids killed varroa mites on the bees and within the brood cells. Queens did not stop laying at these concentrations. Those brood cells adjacent to wicks had bee larvae killed by the acids (which we expected); all brood farther away survived treatment at these levels. Concentrations of formic acid above 18 percent (we tried 25 percent and 20 percent initially) killed younger brood in the cells; older brood survived. Wicks employed at the sides of the brood nest had low kill rates, whereas wicks in the center of the brood nest gave the best results. This experiment will be repeated in 2000, as will most of the other essential oil treatments described above. We plan to make modifications in order to improve syrup delivery to brood cells during honey flows and to develop an improved method of treating with organic acids.
We have collected fall samples of honey from treated colonies and in 2000, will send them to labs for analysis for the presence of essential oils.
We are editing our respective web sites and will have these corrected and operational during January, 2000.
We presented talks, workshops and handouts to several organizations and provided two web sites during the past two years. We have answered many phone calls and emails regarding essential oils and our research, and have given permission to several beekeeping organizations to reprint our publications and methods. We plan to place photos and video clips on our web sites showing the results of our treatments.
We are developing a feeding stimulant (concentrate) containing lemongrass oil and spearmint oil to help beekeepers easily mix solutions of these oils to improve their bees. This concentrate was given out at several beekeeper’s meetings and will be available in Spring, 2000.
December 30, 1999


Tom McCutcheon

Roane Co. Agent
Bob Noel

Tony Delia

Anpak Associates