During the past 15 years, tracheal mites and varroa mites have become major bee pests that seriously threaten the industry in the United States. Mites have killed more than 90% of wild honey bees and 60% of commercial bees in the U.S. (Quarles, 1997). A new pest to U.S. beekeepers — first identified in Florida in 1998—is the small hive beetle (Frazier and Steinhauer, 1999). The following discussion focuses on least-toxic methods of controlling these pests.
Microscopic tracheal mites (Acarapis woodi) lay eggs in the abdominal breathing tubes of the bee, and their larvae feed on the bee after the eggs hatch. The mites came to the United States from Mexico in 1984 (Higgins, 2002). Alternative control methods focus on cultural and chemical manipulations and on mite-resistant bees.
Dr. Eric Erickson at the Carl Hayden Bee Research Center in Tucson, Arizona, commented in an electronic question-and-an-swer forum concerning tracheal mites that "Most colonies in the United States are resistant to tracheal mites. This is largely due to the fact that we have never had a highly effective chemical treatment. Hence, susceptible colonies died and resistant colonies survived" (Erickson, 2002a).
A common treatment for tracheal mites entails mixing 50 grams of menthol with 50 grams of vegetable shortening and spreading it thinly on cardboard sheets that are placed on top of the frames for a total of 25 days (Bosisio, 1990). Since menthol has to vaporize to be effective, it must be used at temperatures of at least 60°F. Also, an entrance reducer should be used and set to the smallest opening, because the fumes are heavier than air and will tend to settle out through the hive entrance (Tabor, 1990). With the smaller entrance, hive ventilation may become a problem during hot days when bees gather at the entrance and vibrate their wings to ventilate the hive. Some beekeepers report that bees have an aversion to
the menthol and that large numbers will initially vacate the hive but eventually return. Purified menthol (from peppermint) and instructions on its use are available from beekeeping supply companies. Spring and fall treatments are recommended.
Information on the next technique, using vegetable oil and sugar, comes from Dr. Tom Webster at Kentucky State University. He suggests mixing equal parts of vegetable oil and sugar into a patty, placing it on a piece of hardware cloth, and resting the hardware cloth on the top bars of the hive. The bees will crawl over the patty and eat some of it. In the process they will gather a small amount of oil on their bodies. The oil will smother the mites. The patty should be replaced if it is consumed before the three-week treatment is over. Again, spring and fall treatments are recommended.
Several researchers have shown that neem can control both tracheal and varroa mites. The neem can be added to sugar water or applied directly on the bees. Dr. T.P. Liu, a Canadian researcher, showed that a concentration of 3 ml of neem extract per liter of sugar syrup significantly decreased numbers of tracheal mites (Quarles, 1997). Dr. A. P. Melathopoulos found that a ten-percent concentration of neem oil placed directly on bees killed more than 50% of varroa mites (Grossman, 1998). Neem has also been shown to be effective against American foulbrood (Grossman, 1998). [Nota bene: As of June, 2000, neem is not registered as a honey bee mite control.]
There is some evidence that tracheal mites prefer new combs to older ones. A study conducted in North Dakota in 1994 found that colonies on new combs were three to four times more likely to be infested with tracheal mites than colonies on old combs (Erickson et al., 1998).
Varroa mites came to the United States in 1986 and have spread through all 48 contiguous states. The mites live in the hive, attach themselves to the bees' abdomens, and suck the bees' vital flu ids. The bees become sick, and the hive slowly dies (Higgins, 2002).
How to Detect
The NebGuide publication Using the Sugar Roll Technique to Detect Varroa Mites in Honey Bee Colonies states:
Globally, [the varroa mite] is the most important pest of honey bees and it has caused extensive losses in feral and managed colonies. Once introduced, varroa mites have never been eradicated from any country or region, [and] beekeepers must adopt an integrated pest management strategy to protect their colonies. Early detection and assessment of infestation levels are important components of a varroa management plan. Since varroa mites feed by piercing the interseg-mental membranes on the underside of the bee's abdomen, they are not easily observed on bees until the colonies are severely injured. Beekeepers need to use a detection technique to check their colonies for mites. In addition to detecting mites, beekeepers need to accurately assess the infection levels to determine when control measures are warranted
The five most commonly used detection and assessment methods for varroa are: 1) ether roll, 2) alcohol wash, 3) brood examination, 4) sticky boards placed on the bottom board, and 5) acaricides with sticky boards. (Macedo, 2001)
These five methods are discussed in the enclosed section "Varroa Jacobsoni", from Diagnosis of Honey Bee Diseases (USDA), available at <http:/ /maarec.cas.psu.edu/bkCD/ Bee_Diseases/varroa.html>.
The enclosed NebGuide publication discusses the alternative technique of using powdered sugar to detect varroa mites, also available at <http://www.ianr.unl.edu/pubs/INSECTS/ g1430.htm>. Another detection method is described in the publication Mite excreta: A new diagnostic tool for detecting Varroa mites! at the USDA/Carl Hayden Bee Research Center website, <http://gears.tucson.ars.ag.gov/rf/de-tect/detect.html>.
For years, the only control for varroa mites (Varroa jacobsoni) has been the miticide fluvalinate (Apistan®), a synthetic pyrethroid. However, beekeepers in Europe and several U.S. states have seen strains of mites resistant to Apistan®. It is only a matter of time before resistance becomes more widespread. It is also important to remember that honey cannot be gathered while Apistan® is in use.
The May 2000 issue of Bee Tidings, a newsletter published by University of Nebraska Extension and the Nebraska Beekeepers Association, discussed the use of Apistan® strips:
Apistan® strips are a highly effective control for susceptible mite populations, but no longer provide adequate control in some beekeeping operations. Beekeepers who choose to use Apistan® should check to determine if their colonies will respond to the treatment prior to spending a lot of time and money on treatment. Dr. Jeff Pettis, a USDA Scientist at the Beltsville Bee Laboratory, described a resistance monitoring procedure in an American Bee Journal article. To conduct the Pettis test, prepare a pint wide-mouth jar by inserting a sugar cube and a note card that has been trimmed to fit the jar. Staple a 3/8" by 1" piece of an Apistan® strip to the card near the top of the card. Prepare a two-piece canning lid for the jar by replacing the center portion with screen wire that will allow mites to pass but not the bees (8 mesh per cm works well). Collect 250-300 mite infested bees in the jar and hold them for 24 hours in a cool and dark place. Invert the jar and shake it several times to recover any dead mites on a sheet of paper. After recovering the mites, place the jars in an oven at low heat (about 140° F.) until the bees are dead. Then, shake the jar again to recover any mites that were not killed by the Apistan® strip. This test will give you a good indication of how effectively Apistan will perform in your colony. Apistan® strips can be purchased in any state and are available from most bee supply dealers. They have a Section 3, or general use, label. (University of Nebraska Extension/Beekeepers, 2000)
Apicure™ is a registered miticide that contains about 65% formic acid, a colorless liquid with a penetrating odor that is found in ants and in many plants. Formic acid controls tracheal mites and is used for the suppression of varroa mites. It has been used for years in Canada and Europe. Apicure™ is a slow-release gel that is sealed in plastic bags that are sliced open and placed in the hives. It should be removed after 21 days and 28 days before honey flow. It should also be used only when daytime temperatures are between 45° and 95°F, with the hive entrance fully open (Apicure, Inc., no date).
A possible option for varroa control was mentioned in the July 2002 American Bee Journal. In the article "Varroa Control with Fungal Pathogens May Be an Option Soon," the authors discuss their research in isolating and screening several fungi that were highly pathogenic to varroa at temperatures similar to average hive temperatures. They state that they hope to offer beekeepers this option in the near future (Kanga and James, 2002).
Several alternative solutions to Varroa control have been studied in Europe. They include lactic acid, oxalic acid, thymol, essential oils, neem oil, and several bio-technical measures. These control measures are discussed in the Swiss Bee Research Center website publication at <http:// www.apis.admin.ch/ english/Themes/ Varroa.htm>. However, according to Blane White, Aviary Inspector in Minnesota, lactic acid and oxalic acid have not been tested in the United States and are not approved treatments. He also comments that thymol has had limited testing in the United States, and that it does work under some conditions. However, there are no approved thymol treatments in the U.S. at present (White, no date).
Using essential oils to kill both kinds of mites has been researched. One of the problems with using essential oils is that many of the compounds are toxic to honey bees as well as mites. Several herbal extracts and essential oils have been tested. For the most current information on using essential oils to control varroa mite, visit West Virginia University's web site at <http:// www.wvu.edu/~agexten/varroa.htm>.
One study tested thymol-based products in Texas, Virginia, and Minnesota (Sanford, 1997). There were good results in Texas and Virginia, but less mite mortality in Minnesota. One reason given for this difference is that higher temperatures in the southern states helped the thymol to diffuse into the colony. Another variable that may have affected the study was the number of hive bodies —in Minnesota, three brood chambers were used, while in Texas only one brood chamber was used. The most effective blend in the study was thymol and citronella.
In the late 1990s, Swiss researchers tried to determine whether organic acids and essential oils affect the taste of honey (Bogdanov, 1999). They found that formic acid was easiest to detect, followed by oxalic and lactic acids. Also, the weaker the natural taste of the honey, the easier it was to detect one of these acids. Of the essential oils, thymol was easiest to detect, followed by camphor and menthol.
More research needs to be conducted. In an APIS newsletter, Dr. Tom Sanford stated, "The take-home message to the would-be experimenter...is that applying oils of essence and related chemicals carries considerable risk and should be approached with extreme caution" (Sanford, 1997).
One method of varroa control involves changing the bottom board of a hive (Sanford, 1998). Often, mites fall off of bees and land on the bottom board. They can then crawl back up into the hive and reattach themselves to bees. A "sticky board" that has been sprayed with something oily (usually PAM™) can be placed over the hive's bottom board and covered with a screen. When mites fall off the bees, they fall through the screen and land on the sticky board and are unable to get back onto the bees. (The screen prevents bees from falling onto the sticky board.) A twist on this method is to create bottom floors made entirely of screen. Not only does this aid in varroa control, it also helps control fungal diseases (Sanford, 1999). For more information on using mesh floors, go to <http://apis.ifas.ufl.edu/ apis99/apjun99.htm#4>. Blane White, Apiary Inspector in Minnesota, says that screen bottoms can reduce varroa populations by 15% to 30%, and that once the screens are installed, no further labor is needed (White, no date).
Thomas Deeby at the Carl Hayden Bee Research Center, in an electronic question-and-an-swer forum, made the following comments about smoker fuel to knock varroa mites off of bees and screened bottom boards to reduce mites in the hive:
Products that have been tried range from menthol, to tobacco, grapefruit and other citrus leaves, and creosote leaves. High heat itself stuns them. Sticky boards and slotted bottom boards also seem to have some measure of success
Natural Products Smoke - Beekeepers routinely use smoke to calm their bees before opening the hive. Tobacco smoke increases mite fall and has been used for both detection and control of varroa. More recently, Dr. Frank Eischen, USDA bee research scientist, demonstrated that creosote bush and grapefruit leaves produce a smoke that can knock down 90% of the mites in test cages. However, excessive exposure to natural product smoke can harm bees. Also, mites are not usually killed by the smoke and may recover if not removed from the colony by a sticky board or other mite trapping device. Mites in brood cells are not affected by natural product smoke. While natural product smoke is not an approved treatment for varroa, there is no legislation prohibiting their use as smoker fuel. With careful attention to bee safety, the smoke of some natural products may be helpful in retarding varroa population growth in colonies.
Anti-varroa bottom boards - A French beekeeper, Jean-Pierre Le Pabic, has devised a bottom board that may help reduce varroa injury. He suggests that in a standard bottom-board-equipped colony, mites that fall from bees are able to easily reattach themselves to another host bee. He designed a bottom board consisting of 12 tubes that run lengthwise with a space between them that permits mites to fall to the bottom, but through which bees cannot pass. He reports that mite populations remain low in hives fitted with this bottom board due to the inability of varroa mites to climb back up to where they can reattach to a new host. Anyone who has worked with sticky boards knows that numerous mites drop to the sticky traps whenever colonies are examined or smoked. This novel approach to varroa control may help reduce beekeeper's dependence on chemical treatments. (Deeby, 2002c)
For more information on the Le Pabic anti-varroa bottom board, see the enclosed article or visit <http://www.apiservices.com/happy keeper/index_us.htm>.
Dr. Pedro Rodriguez has had success using food-grade mineral oil (FGMO). Test results show that FGMO is highly efficient for control of varroa infections. It is economical, non-contaminating, and gentle to the environment. It can be applied every two weeks or so for the entire year. It is used in conjunction with screened bottom boards to prevent mites from re-attaching themselves to bees after falling off. Food-grade mineral oil does not alter the quality of the honey (Arias Martinez et al., 2001). While the use the FGMO is still unregulated and in a testing phase, the potential use of FGMO for control of varroa mites deserves to be considered. Much of the latest information on the use of FGMO and methods of application is located at the website <http://www. beesource.com/pov/rodriguez/>.
Research indicates that smaller starter cells help control varroa mite infestations (Senft, 1997). Foundation sheets (sheets of wax imprinted with base cell sizes) with cells 22% smaller in diameter provided higher winter survival rates for bees.
Another cultural control method is to encourage worker bees to make drone brooder combs. Varroa mites prefer drone brood to worker brood. After the drone pupae have been capped, the drone comb is removed from the hive and discarded. Blane White, Apiary Inspector in Minnesota, states that removing two to three combs of drone brood can reduce varroa population by about 50%. For more information on this method, White recommends the website <http:/ / www.xs4all.nl/~jtemp/dronemethod.html> (White, No date).
Since varroa mites became a major problem, various strains of honey bee have been tested and crossbred in the hope of finding bees that are tolerant to mites—whether through selective breeding for grooming behaviors or for cell-building tendencies. Currently there are at least four options for beekeepers to consider. They are the hygienic bees, Russian bees, SMR (Suppressed Mite Reproduction) Smart bees, or local varroa-tolerant bees.
Hygienic bees spend more time cleaning themselves and their hives, which promotes some resistance to varroa mites. Research has shown that hygienic behavior is heritable, and researchers Marla Spivak and Martha Gilliam have been building up populations of hygienic bees from the ten percent or so that occur naturally. These are now commercially available. Hygienic bees detect and remove diseased bees quickly, before the pest organisms can move to other bees. Hygienic bees are also more resistant to American foulbrood, European foulbrood, and chalkbrood (Sanford, 1998b). The publication The Hygiene Queen provides information on some of the traits that are selected for and also provides the standard quantitative test used. The publication is available at <http://www.beekeeping.com/ar-ticles/us/hygiene_queen.htm>.
Russian bees are a resistant strain of honey bees being developed and tested by the USDA Baton Rouge Bee Lab. These bees evolved in Russia's Far East, where mites and honey bees have co-existed for decades. Commercial evalu ations of Russian bees have shown good mite resistance and exceptional winter hardiness. In tests comparing domestic honey bees with the Russian bees, the varroa mite reproduction was two to three times lower with the Russian bees (Suszkiw, 2001). Contact Dr. Thomas E. Rinderer at the USDA Baton Rouge Bee Lab for information on where to get Russian queen bees (see Further Resources: USDA Research Facilities, for contact information). For additional information on Russian honey bee research, see the Agricultural Research article "Russian Honey Bee Earning Its Stripes" at <http://www.ars.usda.gov/ is/AR/archive/oct01/bee1001.htm>.
The USDA Baton Rouge Bee Lab found a trait of the honey bee that prevents the varroa mite from reproducing and thereby provides genetic resistance to it. This trait is called "suppression of mite reproduction" or SMR (commonly pronounced SMART). The USDA lab has bred a line of honey bees that carry this trait and have released them for commercial sale with several queen bee producers. The SMRD Project at Baton Rouge is described in the publication Breeding Honey Bees that Suppress Mite Reproduction at <http://msa.ars.usda.gov/la/btn/hbb/jwh/ SMRD/SMRD.htm>. In this publication the authors state:
We now have varroa-resistant stocks of bees inbred for the SMR trait, and these colonies greatly limit mite growth. The U.S. queen rearing industry is geared toward the production of naturally mated queens, which makes the production of commercial inbred resistant queens very unlikely (unless queens are mated in an isolated area such as an island). However, queen producers can readily produce hybrid queens. We found mite growth to be intermediate between resistant bees and susceptible bees when resistant queens are free-mated with susceptible drones (Figure 6). Although colonies with hybrid queens (resistant x control) had intermediate populations of mites, they had half the mites found in the susceptible controls. Hence, even hybrid queens should provide beekeepers a tangible level of resistance. (USDA/Honey Bee Breeding, c. 2001)
The Carl Hayden Bee Research Center has demonstrated that it is relatively easy for beekeepers to produce varroa-tolerant bees with their own locally adapted bees, though it does require an elevated level of hive management. The enclosed publication Producing Varroa-tol-erant Honey Bees from Locally Adapted Stock: A
Recipe provides information on what to do and how to do it. This publication is also available at <http://gears.tucson.ars.ag.gov/publ/ tolerant2.html>.
In 1998, the small hive beetle, a native of South Africa, was found in Florida. As of October 2001, the small hive beetle had been found in 24 states, most of them east of the Mississippi River. Migratory beekeepers transport bee colonies from areas known to be infested with the small hive beetle, and the probability that this pest is more widespread is very real due to the migratory pollination demands within the United States. (USDA/BARC, c. 2001)
In an on-line question-and-answer session about small hive beetles, Thomas Deeby stated:
These are extremely tough beetles and very difficult to stop or control. They will either burrow through soft mulch or crawl to a location that is easier for them to access. There are soil conditioners, soil fungus and insect predators that are being currently tested. By the time the beetles pupate, the larvae have caused much damage in the hive, which will not be cleaned up by the bees, and it just escalates from there. This is going to be a very difficult pest to deal with. Pesticides in the hive, in the soil, corrugated cardboard on the bottom board, and other traps seem to be the methods of treatment to date. Keeping strong colonies will help, but not guarantee SHB will not pay you a visit. Moving your hives to break the reproductive cycle of the beetle may work, assuming you have alternate locations for your colonies.
These are some of the things we know about SHB. Two weeks after decimating the comb in a hive, the mature larvae of the small hive
beetle seek the soil under the hive to continue their life cycle. They seem to prefer sandy soil and burrow in 6-8 inches where they pupate and later emerge as beetles. Hard ground only slows the larvae down as they radiate out searching for softer ground. Strong colonies of honey bees can remove some of the larvae in the hive but according to Garth Cambray, in South Africa, the bees do not kill the larva and they drop them up to 50 m from the hive, which allows them to continue their cycle and pupate in the ground.
The small hive beetle is a tough customer. Not only is its exoskeleton hard, providing a solid armor of protection but also it has well-developed wings and can fly at least 5 miles. David Westevelt, state inspector in Florida reports a beetle infestation in a colony 14 miles from the nearest apiary and he has found beetles in feral swarms living in trees. Cold weather has no ill effect as Bill Wilson, Agricultural Research Service, Weslaco Bee Laboratory, Texas, reports that the beetles were found in the center of clusters of honey bees in North Carolina where the night temperature was consistently below freezing. Dr. Lundie who first studied the beetle in 1940 found that adult beetles live up to 6 months. It is known that the beetle can survive days without food so the chance of live beetles being transported in colonies or on equipment is very high.
There is one insecticide currently registered for use on soil in an apiary. It is Gardstar® 40% EC, a permethrin. Beekeepers have used soil drenches of insecticides they might use on ants, such as chemicals approved for fire ants. This is not a legal use. Results are variable and use of permethrin or other insecticides may do more harm via accidental contamination of bee equipment and/or killing of the bees themselves.
Please contact the USDA scientists working in Beltsville and Weslaco for follow-up information. (Deeby, 2002a)
The USDA/BARC Bee Research Laboratory provides the following information concerning the small hive beetle on their website <http:/ / www.barc.usda.gov/psi/brl/bd-shb.htm>.
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