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Fighting for survival against bee mites.

Chemical Controls Keeping Beekeepers Afloat

Everything seemed fine last summer when Jerry Stroope prepared to extract honey from his 4,400 bee colonies in Texas.

But as his employees began examining the hives, they found that some colonies had been wiped out completely - and that in others, there were only a handful of bees left, covered with deadly mites.

Stroope said he lost from 25 to 50 percent of his colonies to a mite called varroa, which he's now controlling with a chemical called fluvalinate. Without it and other miticides, he says, "we'd be out of business."

Stroope's experience has become a familiar one for honey producers since the mid-1980's, when varroa and a second pest, the tracheal mite, were discovered in the United States.

The tracheal mite, Acarapis woodi, was first found in Texas in 1984 and has now infested bee colonies throughout the country. The mite lives, feeds, and reproduces inside the bee's breathing tubes, blocking oxygen flow and eventually killing the bee, says William T. Wilson, an entomologist with USDA's Agricultural Research Service in Weslaco, Texas. He estimates that 50,000 or more honey bee colonies have been lost each year since 1988 because of the tracheal mite.

The varroa mite, Varroa jacobsoni, was discovered in Florida and Wisconsin in 1987, according to Hachiro Shimanuki, who is in charge of the ARS Bee Research Laboratory in Beltsville, Maryland.

Varroa attacks both adult bees and larvae. Young mites developing in the brood cells suck the blood of bee pupae.

As Stroope discovered, a serious infestation of varroa mites can destroy a bee colony quickly. And with few visual warnings, Shimanuki says.

The mite problems couldn't have come at a worse time for the beekeeping industry. Not only have producers been fighting an ongoing battle against bee diseases, but in recent years China has stepped up its exports of less-expensive honey into the United States - undercutting prices of domestically produced honey.

Added to these problems, the mites are a one-two punch that floored some producers and knocked others out of business altogether.

Those who survived are controlling the mites with several chemicals, say Shimanuki and Wilson, who led research teams that studied the chemicals and helped gain Environmental Protection Agency (EPA) approval for their use. "Without these chemicals for controlling mites, I think we'd be finished," says Richard Adee, who's been raising bees since 1957.

Adee, president of the American Honey Producers Association, has about 45,000 bee colonies from the Dakotas to Mississippi, making him the nation's largest commercial beekeeper.

With a peak of about 50,000 bees per colony, Adee looks after more than 2 billion "employees." Without chemical controls, Adee says, he'd lose one-third of his bees to tracheal mites and 20 to 30 percent to varroa each year. "The beekeepers who are surviving are using chemicals and are using them preventively," he says. "Mites will continue to be their number-one problem."

To control them, ARS researchers have been working with private companies and beekeepers such as Stroope and Adee to register four compounds against varroa and tracheal mites.

ARS' research role has been to study the efficacy, residues, and toxicity of the mite controls, Wilson explains. "ARS researchers are making sure the chemicals really work against the mites and that they don't harm the bees or leave unwanted residues in the honey," Wilson says.

Before these chemicals were approved by EPA, the only way to stop the spread of the mites was to destroy infested beehives - a costly practice.

Three of the four chemical compounds have thus far gained EPA approval. They are:

* Menthol. Registered in 1988 for use against tracheal mites, this natural substance, often used in cough drops and other products, kills mites without harming the bees. Since it has to vaporize to be effective, it must be used at temperatures of at least 60 [degrees] F - limiting its use in northern states. "But it has helped considerably against tracheal mites," Shimanuki says. "About 50 tons of menthol a year, on average, were used in beekeeping operations nationwide in the late 1980's."

* Amitraz. Last November, EPA approved this compound under the trade name Miticure, which can be used in northern states and other areas where beekeepers need an alternative to menthol. Amitraz is widely used against a variety of insects, and is impregnated in plastic strips - like a cat flea collar - that are placed inside the hive. When bees walk over the strips, amitraz rubs off on them and kills both mite species without harming the bees.

* Fluvalinate. Approved for general use against varroa mites in 1988, fluvalinate is a synthetic pyrethroid that's used against beetles, moths, and other insects. Like amitraz, it's also impregnated in plastic strips that are placed in the hive.

Shimanuki and Wilson note that all these chemicals should be used in the spring or fall - before or after the main period in which bees gather nectar. Otherwise, chemical residues could wind up in marketable honey.

EPA approval is still pending for a fourth chemical, formic acid. In preliminary studies, Wilson says, it appears effective against both tracheal and varroa mites and is less expensive than the chemicals already approved for use. "It costs about 50 cents per colony to treat with formic acid, compared to $2.50 or $3 for the other chemicals," Wilson says, adding that further studies are needed to determine if formic acid residues could be spread to honey.

Beekeepers say holding down control costs is critical to their businesses.

Adee estimates that mite controls cost him about $135,000 per year. Horace Bell, who operates about 40,000 colonies based in Florida, says treating for mites is a "Catch-22" situation. Using the chemicals raises the cost of the honey, making it more expensive than imported honey. But not treating for mites means certain loss.

"If you don't treat, you're dead; and if you do, you're still dead," Bell says. "We seem to have a handle on how to control them. It's just a matter of the cost of doing it."

The mite problems are even more serious because of the crop-pollinating value of honey bees to U.S. agriculture.

USDA estimates there are 3.2 million bee colonies in the United States (a figure that includes only beekeepers with five or more colonies). In 1991, about 220 million pounds of honey worth about $124 million were produced in the United States.

While honey itself is an important bee product, pollination services measure in the billions of dollars.

For fertilization to occur, pollen - the male sperm in plants - has to be spread from plant to plant. This cross-pollination occurs mainly through wind and insects.

Among insects, bees are the most efficient and dependable pollinators known. As they search for nectar and pollen, they spread the pollen among plants without damaging them.

Economic estimates vary on the value of honey bees as pollinators. A 1992 study by researchers at the State University of New York (SUNY) at Buffalo and Brockport estimated that they are worth between $1.6 and $5.7 billion a year to U.S. agriculture. Other studies place the figure even higher.

USDA estimates that U.S. farmers rent about 1 million bee colonies each year to pollinate a variety of crops such as almonds, apples, alfalfa, apricots, oranges, grapefruits, melons, cucumbers, asparagus, and broccoli.

About 400 agricultural crops worldwide - including 130 in the United States - are pollinated, at least partly, by honey bees, according to the SUNY study.

While the chemicals have given beekeepers a way to control mites, Adee and others worry that the mites will eventually develop resistance to them.

So ARS researchers are studying natural compounds to control the mites. Shimanuki, along with ARS entomologists Nicholas Calderone and William Bruce at Beltsville and University of Maryland researcher Gordon Allen-Wardell, have found naturally occurring compounds that kill tracheal mites. In preliminary lab studies, the most potent have been clove oil and citronellal, which is derived from sources such as lemons and lemon grass and is the active ingredient in the citronella candles common around summer picnic tables.

Clove oil killed 78 percent of mites tested, while citronellal killed 68 percent. "These numbers are promising, because we don't have to kill all the mites to obtain effective control," Calderone says. Field studies of clove oil and citronellal and other potential natural controls of tracheal mites are scheduled for 1993.

"We need to have as many weapons in our arsenal as we can against tracheal and varroa mites," Shimanuki says. "They're so threatening that we can't take any chances."

Hachiro Shimanuki is at the USDA-ARS Bee Research Laboratory, Bldg. 476, 10300 Baltimore Ave., Beltsville, MD 20705-2350. Phone (301) 504-8975, fax number (301) 504-8736 William Wilson is in the USDA-ARS Honey Bee Research Unit, Subtropical Agricultural Research Laboratory, 2413 E Hwy. 83, Weslaco, TX 78596. Phone (210) 969-4870, fax number (210) 969-4884.

Breeding Bees for Nute Resistance

Within the next year, ARS will step up its efforts to fight honey bee mites by releasing bees resistant to the pests.

This spring, the agency is releasing a new honey bee stock from Yugoslavia that has resistance to both tracheal and varroa mites. ARS researchers are also evaluating another stock, from England, called Buckfast, for resistance to tracheal mites and could release resistant bees in late 1993 or early 1994.

While it's common for USDA to release new plant varieties, the Yugoslavian bees are the first honey bees the department has ever released for breeding, according to Ralph Bram, the agency's national program leader for medical and veterinary entomology.

"Insect varieties have genetic traits that can benefit agriculture in the same way that different plant varieties have helped create crops with disease and insect resistance and other improvements," Bram says. "Releasing new bee varieties underscores how seriously we view the mites and how committed we are to helping the beekeeping industry solve the mite problem."

ARS and cooperating scientists have been studying the Yugoslavian bees since 1984. The project, initiated to find resistance to varroa, began 3 years before the mite was discovered in the United States.

But researchers found there was an added bonus: The Yugoslavian bees were also resistant to tracheal mites, according to geneticist Thomas Rinderer, who is in charge of the Honey Bee Breeding, Genetics, and Physiology Research Laboratory in Baton Rouge, Louisiana.

The Yugoslavian bees were brought to the United States in July 1989. They were observed for 6 months in a quarantine apiary on Grand Terre Island off the Louisiana coast to make sure the bees had no dangerous diseases or parasites that could spread to American honey bees. Once they were found to be safe, the bees were moved to the Baton Rouge lab.

Field tests began in 1990, to see if the Yugoslavian bees had more varroa mite resistance than U.S. honey bees. Rinderer says that the Yugoslavian bees are about twice as resistant to varroa mites as susceptible U.S. varieties. "As far as tracheal mites, they're not immune, but they are so resistant that beekeepers wouldn't have to treat their colonies for tracheal mites - just for varroa," Rinderer says.

"For a beekeeper, to save $2 per colony in menthol treatments for tracheal mites is important."

Researchers at Baton Rouge also got good results from a 1991-92 study of the Buckfast bees, which Bram brought into the United States in 1990. The bees are named after the famous Buckfast Abbey, where Brother Adam, a 94-year-old monk, spent about 70 years breeding the bees.

After 6 months in quarantine, the Buckfast bees and several other varieties were evaluated in four states for resistance to tracheal mites, honey production, and other characteristics, according to Robert Danka, an entomologist at the Baton Rouge lab. He said the study's results confirmed earlier reports: Fewer than 10 percent of the Buckfast bees were infested with tracheal mites, compared to up to 80 percent for susceptible bees. Yugoslavian bees also had low infestation levels in the tests.

Danka says that further studies are being done before determining a date for offering breeders stock that incorporates the Buckfast resistance traits. He said the agency's agreement with the abbey prohibits releasing pure Buckfast bees in this country.

Last summer, ARS established a stock release panel that will select specific breeders to increase and maintain supplies of Yugoslavian bees and Buckfast crosses once they're released, says Rinderer. The panel consists of a chairman from ARS and representatives from four industry associations.
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Title Annotation:includes article on mite-resistant bees
Author:Adams, Sean
Publication:Agricultural Research
Date:Mar 1, 1993
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