Virus could explain one symptom of colony collapse
Text Size
HEALTHY VS COLLAPSEDENLARGE | Healthy hives (top) have worker bees covering most combs, but in hives with colony collapse disorder (bottom), a lot of bees leave the hive and don’t return.Custom Life Science Images
There’s bad news for diehards still arguing that honeybees are getting abducted by aliens.
Beehives across North America continue to lose their workers for reasons not yet understood, a phenomenon called colony collapse disorder. But new tests suggest how a virus nicknamed IAPV might be to blame for one of the more puzzling aspects of the disorder—the impression that substantial numbers of bees vanish into thin air.
In tests on hives in a greenhouse, bees infected with IAPV (short for Israeli acute paralytic virus) rarely died in the hive. Sick bees expired throughout the greenhouse, including near the greenhouse wall, Diana Cox-Foster of Pennsylvania State University in University Park reported November 18 in Reno, Nev., at the annual meeting of the Entomological Society of America.
Outdoors, the bees could scatter across the landscape where the occasional dead insect wouldn’t be easily noticed before scavengers found it.
Illusory alien abduction is just one of many symptoms that need explaining, though. The prevailing hypothesis is that multiple forces combine to cause colony collapse disorder, such as pesticide exposure, parasites and possibly IAPV, Cox-Foster reported.
Viruses belonging to the group including IAPV linger in pollen. Cox-Foster said that she and her colleagues have for the first time isolated bee viruses from pollen samples from outdoor hives, though IAPV itself was not found. In another study, the same viral strains showed up in wild bees and neighboring domestic hives. “Our conclusion is the strains are circulating freely,” Cox-Foster said.
So though the viruses don’t affect mammals and bee products would not be a threat to people, infected bees might contaminate visited flowers, perhaps spreading the alien-abduction symptoms.
BEE-SEARCHENLARGE | Jay Evans of the USDA’s Bee Research Lab in Beltsville, Md., studies the effects of pathogens on honeybees.USDA-ARS
Bee scientists first noticed weird bee losses in November 2006 when Pennsylvania beekeeper Dave Hackenberg reported substantial numbers of hives failing for unknown reasons. Honeybees have plenty of reasons to die during winter, but an experienced beekeeper could diagnose the usual ones, so researchers paid attention to Hackenberg.
By mid-December 2006 a team of bee specialists had described the new phenomenon, calling it colony collapse disorder. Colonies otherwise just humming along would lose most of their worker bees in a matter of weeks. The honey, the queen and the very young brood would be largely abandoned without enough of a workforce to tend to them. During that winter, a quarter of beekeepers across the country reported similar disappearances, and 37 percent of U.S. beekeeping operations reported collapses during the following winter.
Roughly a third of food production worldwide depends on animal pollinators such as bees. North American farmers start renting honeybees in February to ensure pollination of the almond crop, and continue renting bees for other crops throughout the growing season. Rental prices for bees are rising, in part because of the collapses. Price changes affect the economics of crops from New England blueberries to Washington state apples.
Even small, stationary operations have been struck by the disorder, said Cox-Foster. “We’ve had some organic growers report collapses.”
Analyses of beekeeping practices dashed notions that some food or treatment to keep pests out of the hives was to blame, she reported. Several studies have failed to find links between colony collapse and acute exposure to crops genetically modified to produce the Bt pesticide.
IAPV surfaced as a suspect in September 2007. Researchers at Columbia University and a consortium of other centers and the USDA reported that sequencing DNA from collapsed and healthy hives revealed a high percentage of the once-obscure virus among the sick hives. At the time, researchers cautioned that the virus might be playing a major role or might just be an opportunist, useful as a marker.
In a perfect world, Cox-Foster would have performed the classic experiments based on Koch’s postulates: giving a suspected pathogen to an organism, seeing if the disease symptoms match and then trying to recover the same pathogen from the newly ill. Infecting free-flying bees with a potential cause of the disorder wasn’t an option, though, so the team experimented in greenhouses.
Those greenhouses stress the bees, says Dennis vanEngelsdorp, Pennsylvania’s acting state apiarist. The stress weakens the bees and may contribute to their collapse, he says, agreeing that the virus certainly isn’t the whole answer. He points out that IAPV has turned up in colonies that don’t collapse, as if they’re usually healthy enough to cope with it.
Exposure to conventional pesticides might also affect bee health. Residues of 75 pesticides have turned up in pollen samples, according to ongoing work by Maryann Frazier of Penn State and her colleagues. The pesticide list includes chemicals that are no longer in wide use, such as DDT.
Cox-Foster said in Reno that she was surprised by the range of pesticides found. One sample included residues of the pesticide aldicarb exceeding levels considered toxic for humans, if humans were eating pollen. (Tests of honey show it’s safe, Cox-Foster said.) Effects of such cocktails on bees, however, still need clarification.
Despite the new evidence, the pieces of the puzzle aren’t falling into a tidy pattern. “I’m not happy about the answer I’m giving you,” says vanEngelsdorp. A mix of miseries seems to drive a colony to collapse, but it’s not always the same mix.
“It’s like heart disease in humans,” he says. “Two people can have a heart attack and not share any underlying causes.”
Click on the image
Reprinted from Science News – December 20, 2008
