Chemical Treatments Evaporators		"A-Z" INDEX &   SEARCH Natural Oils and Other Substances for Mite Control in Honey Bees

The use of natural oils and other substances in the pursuit of mite control in honey bee colonies. This document mainly covers the calibration of LD 50 doses of essential oils with respect to honey bees.

Natural or "essential" oils are produced by plants in order to repel predatory insects or to render the plant in some way toxic to the insect if ingested. There may be a secondary role in attracting would be pollinators, but this is my personal conjecture and is based on the use of some plants and their extracts being rubbed onto hive parts in order to render them more attractive to a passing swarm.

Essential oils have been shown to have antimicrobial, antifungal, insecticidal and miticidal effects on various pathogens and pests under both laboratory and field conditions.

Essential oils have been used for treating honey bee afflictions, including infestations of parasitic mites (varroa and Acarine (tracheal) mites). Laboratory and field tests have shown that they are between 50% and 95% effective in this role.

They do cause contamination of wax and honey, but the levels are minimal. Three delivery methods are used in bee hives... Slow fumigation, fast fumigation and admixture with sugar syrup feed, which has both a direct ingestion component and a certain amount of slow fumigation.

The terms 'slow' and 'fast' are used here to indicate the difference between passive fumigation by a bottle with a wick (or a felt pad in a honey jar lid) and the burning of pungent leaves in a smoker or delivering an aerosol of the oil compound.

Historically 'Oil of wintergreen' (methyl salicylate) has been used against acarine mites for a century or more. Although thyme oil and eucalyptus oil have also been used. Menthol crystals at a rate of 50g per hive are most favoured in USA. There is a newly formulated micro encapsulated version of menthol which is now being added to honey bee feed. This material has shown promising results so far.

The commonly used essential oils for varroa control, are thymol, eucalyptus, and wintergreen. These oils can be applied singly or in concert. When applied as fumigants, the effectiveness of thymol and other essential oils against varroa mites depends greatly on temperature, time of the year and colony strength. Due to the inconsistency and unreliability of essential oils for mite control, they cannot be used alone. However, their use does fit well into Integrated Pest Management (IPM) programs for alternating use with other control measures. New efficient methods for applying these oils and finding the right time of the year for application to bee colonies are required to produce reliable effective control of mites.

The following oils were hand fed to honey bees to determine their toxicity to honey bees.

Other botanical oils underwent preliminary testing for control of varroa, acarine (Tracheal mites) and American Foul Brood (AFB)... They were pinene, oil of wintergreen, thymol, clove oil, cinnamon oil and Neem oil. Neem oil, but more work needs to be done, and is planned, with this material.

Essential Oils and their Toxicity to Honeybees

Research Results

Methodology

Three hours prior to each feeding trial, bees were collected from honeybee colonies in commercial apiaries and brought to the laboratory in cages. The bees were kept at room temperature, without food to make them hungry.

The feeding solutions were prepared by dissolving various concentrations of the oils to be tested in 99.9% ethyl alcohol. Appropriate concentrations (see below) for detailed study of LD50 (the concentration of material required to kill 50% of the test animals) were determined on the basis of toxicity of three initial concentrations, 10ppm, 100ppm, and 1000ppm. Solutions were stored in the freezer prior to use and kept on ice during the experiments, except when be actually fed to the bees.

The preparation resembled a liquid sandwich of sugar syrup, the oil in solution in alcohol, and another layer of sugar syrup in Hamilton syringes.

This way, the sugar syrup (50%) induced the bees to start feeding and to continue to do so on the otherwise unpalatable alcohol and oil solution. Each liquid sandwich comprised 5 µl of 50% sugar syrup, 10 µl of the compound dissolved in alcohol and 5 µl more of 50% sugar syrup.

Bees were held between the thumb and forefinger during feeding. In most cases, the bee extended its proboscis with the intent of feeding. When the proboscis was not extended, the needle point of the syringe was used to unfold it. This would induce the bees to begin feeding in the normal way. Often, bees would feed on the syrup, but then would stop feeding before the entire 20 µl had been consumed. In these cases the proboscis would be forcibly re-extended and the process of feeding would slowly continue.

For each concentration of each essential oil, four cages, each with 20 bees, were fed the liquid sandwiches. In addition, four cages of 20 bees were fed 50% sugar syrup (20 µl) and four cages of 20 bees were fed 99.9% ethyl alcohol sandwiched between sugar syrup (5 µl sugar syrup, 10 µl ethyl alcohol and 5 µl sugar syrup). Sugar syrup control cages and ethyl alcohol control cages were fed each time a feeding trial was conducted.

Cinnamon oil was fed at the following concentrations: 10ppm, 50ppm, 100ppm, 150ppm, 250ppm, 300ppm, 400ppm, 500ppm and 1000ppm.
Clove oil was fed at the following concentrations: 10ppm, 50ppm, 100ppm, 250ppm, 300ppm, 400ppm, 500ppm and 1000ppm.
Neem oil was fed at the following concentrations: 10ppm, 100ppm and 1000ppm.
Pinene was fed at the following concentrations: 10ppm, 50ppm, 100ppm, 250ppm, 500ppm, 750ppm, 1000ppm, 1500ppm, 2000ppm and 3000ppm.
Thymol was fed at the following concentrations: 10ppm, 50ppm, 100ppm, 125ppm, 150ppm, 200ppm, 250ppm, 500ppm and 1000ppm.
Oil of wintergreen was fed at the following concentrations: 10ppm, 100ppm, 250ppm, 500ppm, 750ppm, 1000ppm, 1500ppm and 2000ppm.

Bees were fed 50% sugar syrup for three days following the feeding trials. During this time the number of dead bees was monitored at 24, 48 and 72 hours.

Preliminary results

Control cages that were fed sugar syrup had an average of 2 dead bees over 72 hours. Bees fed the ethyl alcohol sandwich without any oils had an average of 3.5 dead bees over 72 hours. Thus, the physical effects of force feeding were minimal and the ethyl alcohol we used had little toxicity for the bees.

The following is a list of the approximate LD 50's for each of the oils tested together with menthol from a previous experiment.

Substance	LD 50
Menthol	unable to cause mortality with highest doses administrable [1]
Cinnamon oil	150 ppm
Clove oil	200 ppm
Pinene	1500 ppm
Thymol	100 ppm
Oil of wintergreen	500 ppm.
Neem oil	from 100 ppm to 1000 ppm (the bees did not take well to being fed Neem oil)

Conclusions

Establishing the toxicity of these potentially useful botanicals is an important step to understanding dosage response, and the risks of administering these materials orally to bees for their protection against mites. Although a given compound may be efficacious against mites, if its toxicity to bees is high then there is great risk in using it.

Materials such as thymol may continue to be useful as fumigants and in topical application, but would have to be used with care as an oral medicament. Pinene, on the other hand, may be valuable in killing mites on and in the bodies of honeybees by its relatively low toxicity to bees when they ingest it.

Phase I of this research was unable to proceed with toxicity trials against mites and micro encapsulation because matching funds were still pending. In Phase II of this research, it is intended continue the work on the toxicity of the botanicals to mites and investigate the potential for micro encapsulated formulations being used as medicaments.

Reporting Activities

Nasr, M. and P. G. Kevan. 1999. Diseases and parasites, eradication or management: what strategy for honey bee health? Bee World 80: 53-54
Medhat Nasr, and P. G. Kevan. 1999. IMP for diseases and parasites in honeybees Pest Management News 10 (4): 3.
Skinner, A. J., M. E. Nasr and P. G. Kevan. 1998. Impacts of tracheal mites on the thermoregulation and over wintering of honey bees. Presented at Entomological Society of America Annual Meeting Las Vegas, Nevada. (8 - 12 November, 1998) and Presented at Entomological Society of Ontario Annual General Meeting, Sudbury, Ontario (October 1998).
Kevan, S. D., Medhat E. Nasr, and P. G. Kevan. 1999. Feeding menthol to honeybees (Hymenoptera: Apidea): entry and persistence in haemolymph without causing mortality. The Canadian Entomologist 131: 279 - 281

Acknowledgment is given to... An article titled "Botanicals for Mite Control", published in Hivelights Vol 12 #4, November 1999. The work for which was carried out by... Peter G. Kevan, Medhat Nasr and Ms. S.D. Kevan.

References

[1] (Kevan et al.1999)

Originated... 07 March 2004, Upgraded... 31 August 2006,