SEEKING SYMPTOMS USDA researchers rate honeybee colonies for signs of disease.
The Western honeybee has been receiving a raft of publicity in recent years. The health plight of Apis melliferahas been the subject of news articles, television profiles, and movies with titles like “The Vanishing of the Bees” and “The Last Beekeeper.”
The attention is deserved; bees in the U.S. and Europe are facing a crisis, and many are dying. According to the U.S. Department of Agriculture, symptoms that have been grouped together into what is called colony collapse disorder, or CCD, caused beekeepers to lose 34% of their bee populations in 2010—and that came after three years of similar annual losses.
The losses are worrisome because honeybees are important to the national economy. They pollinate 130 crops, adding a total value of $15 billion to the agriculture industry, USDA says. Pollinating California’s almond crop alone requires the labor of more than 1 million bee colonies each year, either raised locally or hired from out of state, the California Almond Board points out.
Despite the attention, comprehensive solutions to the bee problem have yet to emerge. Rather than a new, exotic disease, researchers now think the bees have been weakened by a combination of long-existing known factors, including parasites, viral diseases, and exposure to pesticides.
One thing the publicity has done is spur renewed interest in finding new treatments for pests and diseases that have been around for decades. Small firms focused on animal or honeybee health are joining larger agricultural chemical companies such as BASF and Bayer CropScience to introduce new products. The need is acute because the chemical treatments beekeepers counted on in the past no longer work reliably. The new treatments, coupled with improved pest management practices, may help beekeepers ward off CCD.
“We realize more and more the number of stresses, such as high virus loads, high loads of other pests, and pesticide presence, that are impacting bees these days,” says James D. (Jamie) Ellis Jr., assistant professor of entomology at the University of Florida. “The compelling data that keep coming out say bees can handle one or two stressors, but when you get three or more you see a real decline. The cause of CCD is more likely multiple stressors than one.”
The most prominent member of the likely group of villains is the aptly named parasitic mite Varroa destructor. Research has not singled out varroa as a cause of CCD—it is present in both CCD and non-CCD colonies—but bee experts stress that varroa is the most common killer of honeybees overall. For that reason, most treatments focus on ridding bee colonies of the crablike mite.
Varroa was discovered in bee colonies in the U.S. in 1987; it had been seen in some areas of Western Europe a few years earlier. Globalization had carried the mite from Asia, where it evolved as a parasite of Apis cerana, an Asian honeybee. The parasite reproduces in the honeybee brood cell, where bee larvae grow. Adult female varroa mites then latch onto adult bees, sucking out hemolymph—bee blood—and spreading diseases such as the virus that causes so-called deformed wing disease.
VAMPIRE MITE An adult worker honeybee with two varroa mites on its thorax.
The first products to control varroa in bee colonies were Apistan, a pyrethroid based on the active ingredient τ-fluvalinate, and CheckMite Plus, made with coumaphos, an organophosphate. Both were effective, killing 95% of the mites in each colony. But the rapid 10-day reproduction cycle of the varroa mite meant that resistance to the treatments had to be carefully managed.
Beekeepers figured out that fluvalinate is also the active ingredient of other pesticides, and that’s when things really started to go wrong, according to Mark Newberg, director of corporate affairs at Central Health Sciences, the maker of Apistan. “In an attempt to stretch a dollar, beekeepers have been known to soak a rag or wood chips in the active ingredient to use in the hive.” Using products not intended for honeybees can cause overdoses or underdoses that can lead to resistance. Apistan can still work to control mites, Newberg says, if used according to directions and rotated with other treatments.
Until recently, beekeepers had few other treatments to rotate with the old standbys. Then last March, BASF teamed with the tiny Canadian firm NOD Apiary Products to bring Mite Away Quick Strips to European beekeepers. The strips contain formic acid, starch, and sugar in a BASF-made biodegradable plastic dosing package. Formic acid is a natural component of bee sting venom and has been proven as a miticide, according to BASF.
“The formic acid works under the capped brood in the beehive, where the mites reproduce,” explains Renate Wapenhensch, BASF project leader. “It is effective within the time span when fertilization takes place by working on the male mite, which comes out first and has a very soft shell, before the female mite hatches.”
In November, Bayer CropScience announced that it had acquired a varroa mite control product from the U.K. firm Exosect. The product combines the active ingredient thymol, a natural biocide derived from thyme oil, with a powdered natural wax. The powder adheres to bees via electrostatic attraction, eventually dropping into the brood cell.
Bayer plans to launch the thymol-based product in the U.S. this year and in Europe starting in 2012. Bayer’s first nonsynthetic product for the beekeeping market, it will join CheckMite Plus and the pyrethroid Bayvarol.
Bayer will face competition from two thymol-based products recently introduced in the U.S. and Europe. Apilife VAR, made by French firm Chemicals Laif, also includes smaller amounts of eucalyptus oil and menthol. Apiguard, which features thymol in a gel matrix, is manufactured by Vita Europe, a small U.K. firm that is focused on the honeybee market.
Thymol kills varroa by disrupting the mites’ cell walls, says Max Watkins, director of R&D at Vita Europe. “There are only a few classes of compounds used to control any diseases on honeybees because bees are so sensitive to chemicals,” he points out. Adding to the development challenge is the small size of the honeybee market. “They are tiny markets, but there are a lot of them, so it adds up and keeps a small company going,” Watkins says.
Bee colonies that are stressed by invasion from varroa or other pests can also fall victim to infection from viruses that are normally present in the colony but are otherwise often harmless.
Beeologics, a small firm with a research base in Israel, says new treatments based on RNA interference can help protect bees from viral infections, including the newly discovered Israeli acute paralysis virus. When a virus enters a bee’s cells, the RNAi prevents it from producing proteins and replicating. “Where for humans, big companies are struggling with RNAi delivery, in insects the delivery is much easier—it works with the insect’s immune system instead of against it,” explains Chief Executive Officer Eyal Ben-Chanoch.
“People told me that breeding honeybees resistant to varroa would be like breeding sheep to be resistant to wolves.”
Other risks to honeybees may come from the environment. The specter of CCD has made beekeepers wary about the pesticides that bees contact as they forage for pollen as far as three miles from the hive. “When you actually sample a colony, by far the top two residues are fluvalinate and coumiphos,” University of Florida’s Ellis says. Neonicotinoids, a common class of insecticides that has been suspected of causing health problems in bees, have been found in some colonies, along with other herbicides and insecticides. “But it’s what we put in as the bee industry that comes up in high levels,” he says.
Ellis recommends that beekeepers follow integrated pest management (IPM) to keep their bees healthy and productive. The strategy allows use of natural or synthetic controls when required, but also applies management practices to keep pest and disease levels to an economically viable level. For example, beekeepers can populate hives with bees bred to be resistant to common pests and diseases.
One bee breeder risked his family business to create such a bee. “People told me that breeding honeybees resistant to varroa would be like breeding sheep to be resistant to wolves,” recalls Danny Weaver, owner of honeybee supplier BeeWeaver. Varroa mites decimated his bees in the late 1980s. In 1992 Weaver began breeding the survivors with an eye toward resistance to the mite and, later, to the deformed wing virus. By 2001, he says, “we went cold turkey; we have not treated our colonies with pesticides for 10 years.”
Both Ellis and Weaver report that IPM methods have caught on more strongly with smaller or hobbyist beekeepers than with the larger operations such as those that pollinate California’s almond trees. Beekeeping “is the last agriculture industry to embrace IPM, because the pests have only been with us for the past 20 to 30 years,” Ellis says.
Vita Europe’s Watkins says CCD and the surrounding publicity have had a silver lining for the honeybee industry. “The industry is starting to grow, if anything. We’ve lost a lot of bees through health problems over the last few years, and because of that it’s in the news. There have been a lot of new beekeepers who have come in, and it’s really starting to help now.”
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © 2011 American Chemical Society
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