The case of the disappearing bees: scientists investigate the cause of millions of disappearing bees.
Scientists were alarmed. Bees pollinate many flowering plants, enabling them to produce fruits, nuts, and vegetables. Although wind pollinates crops such as wheat and other grains, one third of the human diet comes from crops that rely on insects to transfer pollen. Honeybees do the bulk of this work. Since CCD could put human food supplies at risk, scientists were called in to investigate the bees' disappearance. But the scientists were stumped. They had never seen so many bees vanish without a trace.
What do scientists do when faced with a mystery such as this? They turn into detectives.
BUZZED TO THE SCENE
A Florida beekeeper first blew the whistle on CCD last November. He was preparing to transport his bee colonies to California to pollinate almond trees. Beehives are normally buzzing with activity (see Nuts & Bolts, right). But when he inspected his hives, he was shocked to find that his formerly strong colonies had turned into bee versions of ghost towns. He had lost nearly two thirds of his 2,900 colonies.
University of Montana entomologist Jerry Bromenshenk was one of the experts on insects called in to investigate. He'd seen honeybee colonies wiped out before by culprits such as chemical pesticides, tiny arachnids called mites, and viruses (particles that invade cells and then multiply). These offenders leave tell-tale evidence, such as piles of dead bees or diseased brood--beekeeper lingo for developing bees. But in this case, the adult bees had vanished, leaving behind only the queen, young bees, and healthy-looking brood. The current disappearance didn't fit the profile of any known cause.
Observers spotted another strange phenomenon. Normally when bees abandon a hive full of honey, looters such as other bees and animals grab their fill. "Bees generally take every opportunity to steal honey from their neighbors," Bromenshenk says. But other creatures steered clear of the hives affected by CCD.
Strange reports of missing bees poured in from other states. Members of Bromenshenk's team traveled around the country to inspect collapsed hives. "We were seeing the identical problem in multiple states," Bromenshenk says.
To crack this mystery, the team's strategy was first to collect samples the way forensics experts do at a crime scene. But since the bees had vanished, Bromenshenk compares the challenge to trying to solve a crime where "you don't have the bodies." If the culprit was a disease, the missing bees might have carried away the evidence. But the team hoped for the best, gathering samples of the remaining bees, honey, wax, and brood for possible clues.
Back in the lab, researchers dissected some samples to look for visible clues such as mites. They didn't find enough of the tiny parasites to believe that they could be the main problem. Other clues, such as microscopic viruses, are trickier to detect. For help, the team turned to a military lab that studies human diseases using a device called an Integrated Virus Detection System (IVDS).
The IVDS can be used to size and count intact viruses. Researchers had never used IVDS on bees, so they weren't sure how to prepare the tiny samples for testing. But they developed a way: "They grind up the bees in a coffee grinder and make 'bee smoothies,'" Bromenshenk says. Then, the IVDS spins the slushy concoction in a centrifuge, which separates larger, denser particles from smaller ones. That enables the device to hunt for the presence of tiny viruses and fungi.
Once IVDS detects viruses, investigators ship the microscopic suspects to a different lab for identification. So far, this method has turned up several viruses, plus a fungus called Nosema ceranae that's been a problem for bees in the past. Additional labs are testing other bee samples for pesticides or other chemicals that may have driven the insects away.
The investigation team also surveyed beekeepers to identify or eliminate possible suspects. The survey revealed that many bee colonies experienced a stressful event--such as confronting unusually dry weather or being trucked across the country to pollinate crops--right before the bees disappeared. This suggested that a combination of factors could be involved, with a stressful event weakening colonies before a disease or chemical moved in.
As Science World goes to press, no one culprit has been singled out for causing CCD. But Bromenshenk vows that scientists will continue to monitor the situation. He says: "Scientific sleuthing takes a long time; it requires hard work and patience. Unlike the forensics studies on TV, we don't solve mysteries in an hour."
nuts & bolts
ANATOMY OF A BEEHIVE
When scientists began investigating the disappearance of honeybees across the United States, one of the first things they did was check out individual hives. What they found was disturbing: Hives that would normally be abuzz were all but devoid of adult bees. Left behind were the queen, young bees, and healthy-looking developing bees. How does that compare with a thriving hive? The diagram below shows the activity that takes place in a healthy beehive.
(1) Each honeybee hive serves as a home, food factory, and bee nursery. The hive is made from beeswax, a substance that honeybees produce with their bodies.
(2) There is usually only one queen in a honeybee colony. Soon after she is born, she goes on a "wedding flight" and mates with drone bees. She spends the rest of her life laying eggs inside the hive.
(3) Infants are raised in "brood cells." The queen lays an egg In each one. There, the egg hatches into a larva. The larva develops into a pupa, and emerges as a fully formed adult.
(4) Most bees in a colony are worker bees. Worker bees are females, but they will never lay eggs. They tend to the queen and infants, make wax, gather nectar, and make honey.
(5) Drones are male bees. Their only job is to mate with the queen. Then, they hang around the hive until the workers force them out at the end of summer. Outside, they die of cold and starvation.
Want to learn more about honeybees? Visit the National Honey Board: www.honey.com/consumers/kids/beefacts.asp
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|Title Annotation:||LIFE: INSECTS|
|Date:||Sep 3, 2007|
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