A European honey bee (Apis mellifera) with a Varroa mite on its back

Many fruit, nut and berry crops depend on honey bees for pollination,but more and more bee colonies are dying each year. Parasitic mites,viruses, and pesticides may all play a role, but as Véronique LaCaprareports, researchers are still looking for a way to stop the die-off.

Honeybees are the most valuable pollinators of agricultural crops worldwide.In the United States, approximately 130 crops depend on honey bees forpollination. Their work is worth about $15 billion a year.  

DennisVanEnglesdorp is Pennsylvania's acting state apiarist. He's responsiblefor tracking the health of the state's commercial honey bee colonies,and he estimates that one in every three bites of food we eat aredirectly or indirectly pollinated by honeybees. "Honeybees are themoveable pollination force in modern agriculture."
   
Almonds,blueberries, and apples; carrots, onions, and squash - all of thesefruits and vegetables grow in different parts of the country and bloomat different times of the year. So, to meet the pollination demand,commercial beekeepers truck their hives around the country. A singlebeekeeper may move tens of millions of bees, covering thousands ofkilometers in a single trip.

"So all your fruits and vegetables,all your flowering plants require insect pollination," saysVanEnglesdorp, "and honey bees do a majority of that pollination."

Parasitic Varroa mites are a major cause of U.S. bee colony declines

Inthe 1940s and '50s, there were approximately five million managed beecolonies in the United States. Today, that number has dropped to lessthan half that. Severe declines began in the 1980s, with the accidentalintroduction of a new parasite called the varroa mite.

"It'sactually an amazingly large parasite," describes VanEnglesdorp. "If wewere a bee, it would be like a dinner plate feeding on us." The mitehas very sharp mouthparts, which it uses to pierce the skin - orexoskeleton - of the bee. Van Englesdorp says that varroa actuallyspits inside the bee, "and in that spit we believe that there's aprotein which acts a lot like AIDS virus does in the fact that itbreaks down the insect's immune system."

The mite can alsotransmit viruses and other pathogens from bee to bee, and wipe outentire colonies. According to VanEnglesdorp, varroa is the biggestchallenge facing commercial beekeepers: "it still kills most of thecolonies in the country."

Jeff Pettis, lead researcher at the U.S. Department of Agriculture's Bee Research Laboratory, holds a frame of honeybees

Jeff Pettis is the lead scientist atthe U.S. Department of Agriculture's Bee Research Lab, just outside ofWashington, D.C. Pettis and his team have been studying a more recentand mysterious threat to honey bee colonies. Honeybee colonies usuallysuffer a loss of about 15 to 20 percent each year. "Our last two yearswe've been over 30 percent losses," says Pettis, "and so this is whatwe're calling this phenomenon of CCD, colony collapse disorder."

CCDlooks very different from other causes of bee death, and it happensmuch more quickly: within just a few weeks, most of the adult workerbees disappear from the hive, leaving the queen and all the young beesbehind.

Since CCD was first reported, researchers have beenscrambling to find a cause. They've looked at parasites, viruses,pesticides, and even colony management problems like poor nutrition andtransportation-related stresses.

Experimental beehives at the USDA Bee Research Laboratory. A single commercial beehive can house as many as 50,000 honey bees

Pettis says that researchershave already done enough testing that if one new pathogen or otherproblem were causing the bee deaths, they would already have identifiedit. "We think it's a complex, maybe even a syndrome - things that arecoming together to cause the losses of bees."

The lack of clearanswers worries Dennis VanEnglesdorp. "What's really frightening aboutthis new condition is we don't know what causes it, so we don't knowhow to stop it." He says that the mobile, commercial honeybeeoperations that we rely on to pollinate different crops across thecountry are in real danger. In a single year, "they can lose 30 to 50,sometimes 80 percent of their colonies." Van Englesdorp says beekeeperscan absorb that kind of loss for a year or two, "but they can't do itthree years in a row and stay in business."

And bee declines arenot limited to the United States. "We're hearing reports from Europe,from Canada, and from South America, even some from Asia - wherehoneybee populations are collapsing and decreasing."

There arestill enough bees in the U.S. to meet demand, but VanEnglesdorp warnsthat continued colony losses could threaten the production of somecrops, and drive more and more beekeepers out of business.