APIS Volume 6, Number 11, November 1988
In this issue
- Varroa Video Released
- Menthol Crystals and Tracheal Mites: Literature Review
VARROA VIDEO RELEASED
A video produced at the University of Florida, funded by USDA's Animal Plant Health Inspection Service (APHIS) and the Florida Cooperative Extension Service, will be made available nationwide. This information comes from Milton Holmes, Operations Officer of Domestic and Emergency Operations, APHIS. The video, entitled "Varroa Mite Detection," will be distributed to members of the Apiary Inspectors of America (AIA) and Plant Protection and Quarantine (PPQ) offices.
There is no copyright protection on the video designed to acquaint both beekeepers and regulators with techniques to detect Varroa. A copy is also being made available in the IFAS Editorial Film Library. Its number is VT- 249.
To order, send a blank tape to the author.
MENTHOL CRYSTALS AND TRACHEAL MITE: LITERATURE REVIEW
I have received many requests about use of menthol to control the honey bee tracheal mite, Acarapis woodi. Large quantities of menthol are being used nationwide for mite control. As background on the material, the following information is taken from the May, 1988 Bee Aware, extension beekeeping newsletter of the Pennsylvania Cooperative Extension Service, authored by Dr. Clarence Collison:
Menthol is a crystalline alcohol obtained from oil of peppermint that is commonly used for odor and cooling properties in candies, cigarettes, shaving creams, etc. (Ferguson 1986). Early work at the USDA Honey Bee Research Lab in Weslaco, Texas showed that 50 g (approximately 2 oz.) of menthol crystals killed 85% of the mites in three days time. In four weeks, all of the mites were dead. Menthol packets were made from window screen and placed on the bottom board of heavily infested colonies. These packets lasted two to three weeks.
Further testing in New Jersey indicated that menthol was excellent in controlling tracheal mites in overwintered colonies (Herbert, Shimanuki and Matthenius 1987). Treatments were initiated in late winter in order to study the relationship between air temperatures and vaporization rates of menthol and because colonies are less populous during this time of year which may expedite mite control. In addition, possible menthol residues in honey should be minimized because no surplus nectar flow occurs in New Jersey until May. Mite infestation levels prior to treatment ranged from 2% to 46%. Plastic window screen packets (17 X 17 cm, 15 mesh) containing 50 g of crystalline menthol were placed on top of the brood nest. The infestation levels decreased 3 weeks after the initial treatment (11 March 1987) and after 9 weeks all treated colonies of bees were mite free. The mite infestation levels of the untreated controls increased dramatically during the study. Control occurred once daytime temperatures exceeded 70 degrees F. The menthol was removed and replaced with fresh material every three weeks (2 April, 24 April and 15 May). After the initial treatment, the bees were observed to determine their reaction to the menthol crystals. They did not break the winter cluster nor did they tend to move from under the bag of menthol. Later in the season, frames of brood were found under the menthol packets.
In a second study, Herbert, Shimanuki and Matthenius (1988) evaluated the effectiveness of menthol crystals placed in various positions within the colony as well as determining the ideal time of year to begin menthol treatments. Under warm conditions the vaporization of menthol is often accelerated which could result in brood and adult bee mortality. Under cold conditions methods to increase vaporization are needed. Positions tested within the colony were: (1) screen menthol bags placed on top of bars of the combs directly over the winter cluster; (2) same as the previous treatment except the bottom entrance was taped shut and a small entrance in the top hive body was provided; (3) four sponges (approx. 7 in. X 4 in. X 2 in.) each soaked in a 95% ethyl alcohol-menthol solution, and placed inside an empty hive body placed over the clustered bees; (4) a petri dish containing 50 g of solidified menthol inverted over the clustered bees; (5) two cloth bags, each containing 25 g of menthol were hung between frames on either side of the clustered bees and (6) untreated controls. The colonies were treated twice during the study: Feb. 4 and April 15.
Administering the menthol crystals by placing screen bags containing 50 g (approx. 2 oz) on the top bars over the clustered bees appeared to be the best method of application in colder climates. No differences were seen between colonies in which the bottom entrance was taped shut and those with the bottom entrance open. Since the vapors of menthol are heavier than air, they tended to settle inside the colony. Also, placing the menthol over the cluster of bees utilized the heat produced by the bees to increase vaporization rates.
On May 7, all colonies with the crystals placed above the winter cluster were free of mites. Effective control did not begin until after the second treatment of menthol was applied on April 15. At that time, daytime temperatures ranged from 30-79 degrees F. The menthol vaporization increased once daytime temperatures exceeded 70 degrees F. Treating the colonies of bees with menthol soaked sponges also provided excellent control, and on May 7 these colonies were mite free. This method, although effective, requires more labor than the screened bags. Complete mite control was not achieved with the inverted petri dish or by hanging two bags of menthol on either side of the clustered bees.
While menthol treatments have proven effective in controlling the tracheal mite under certain conditions and are being widely used by some beekeepers, there is the potential of having menthol residues in treated colonies. Rivera, Moffett and Cox (1987) analyzed samples of wax, bees and honey for menthol residues with gas chromatography. An average of 0.28 ppm menthol was found in honey taken from 40 colonies at Weslaco, TX prior to menthol treatments. Menthol was detected in twelve of these colonies. After these samples were taken, the colonies were treated with three dosages of menthol in aluminum screen packets placed on the bottom board for 62 days. The screened packets contained 0, 10, 25 or 50 g of menthol. Fresh packets were given the colonies every 20-21 days.
Menthol was found in some of the untreated colonies on each of the 3 sampling dates. Menthol residues increased in the honey as the dosage applied increased and they averaged ca. 2 ppm from colonies exposed to the 50 g packets of menthol.
Similar tests were conducted in 40 colonies near Soto La Marina, Mexico. When the test was completed, only one of the untreated colonies had detectable menthol residues (0.55 ppm). At the same time, honey from the 10 g treatment averaged 1.28 ppm menthol, compared to 3.28 ppm in the 25 g treatment and 8.39 ppm in the 50 g treatment.
Additional tests in Nebraska using petri dishes containing 25 g of resolidified menthol was placed on the top bars of 32 of 48 colonies for 42 days. At the end of the treatment period, menthol residues from the untreated compared to the treated colonies were respectively 0.35 vs 1.39 in honey, 2.10 vs. 24.37 for adult bees and 9.48 vs. 77.62 for beeswax.
A 17-day study was also conducted in Weslaco, TX to determine how menthol residues accumulate in honey. Two petri dishes each containing 25 g of menthol were placed on the top bars of 5 colonies. One colony was not treated. The daily maximum temperature ranged from 90-100 degrees F. Menthol residues in capped honey in the treated colonies were less than 0.10 ppm when the test started. Residues in the honey peaked at 9.38 ppm by the 11th day, but dropped to 6.30 on the 17th day. The menthol evaporated completely in some of the dishes before the end of the test, which probably accounts for the drop in residue levels. Newly stored uncapped honey had 72 ppm menthol at the end of the test. During this 17-day test period, menthol residues in the untreated colonies remained below 0.10 ppm.
Honey from an untreated apiary near Mercedes, TX contained 1.18 ppm menthol, while honey from Georgia contained 0.12 ppm. Herbert, Shimanuki and Matthenius (1988) also analyzed honey and wax for menthol with high performance liquid chromatography during their New Jersey test. The menthol content of honey was highest (123.5 ppm) when the menthol was placed in cloth bags that were placed around the clustered bees. When the menthol was placed in screen bags (bottom shut), the menthol ranged from 3-46 ppm. When the entrance was open, the menthol levels were from trace- 31 ppm. In the sponge treatment, the menthol levels ranged from trace- 37.9 ppm, and only traces were found when the menthol was placed in petri dishes. The controls contained 0.7 to 3.3 ppm menthol. Since menthol is a natural product obtained from peppermint or other mint oils, there is the possibility that menthol may be naturally present in honey in small quantities.
These research results certainly indicate that menthol levels in honey increase as the dosage applied increases, especially when treatments are placed above rather than below the bees. Treatments should begin early in the season in colder climates and discontinued before any major nectar flow to prevent the possibility of further honey contamination. To date, since menthol crystals are derived from a natural compound, the Environmental Protection Agency has not issued any complaints against its use in the honey bee colony.
Literature Cited:
- Ferguson, J.L. 1986. Menthol crystals reduce tracheal mite populations. American Bee Journal 126 (11): 760.
- Herbert, E.W. Jr., H. Shimanuki and J.C. Matthenius Jr. 1987. The effect of two candidate compounds on Acarapis woodi in New Jersey. American Bee Journal 127 (11) 776-778.
- Herbert, E.W. Jr., H. Shimanuki and J.C. Matthenius Jr. 1988. An evaluation of menthol placement in hives of honey bees for the control of Acarapis woodi. 128 (3): 185-187.
- Rivera, R., J.O. Moffett and R.L. Cox 1987. Menthol residues in honey, beeswax and honey bees. American Bee Journal 127 (12): 850.
Sincerely,
Malcolm T. Sanford
Bldg 970, Box 110620
University of Florida
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©1988 M.T. Sanford "All Rights Reserved
