In October 2006 Dave Hackenberg, a professional migratory beekeeper, dropped off 400 colonies of bees from Pennsylvania to spend the winter in the warmth of central Florida. When he returned to his Florida apiary a month later he was surprised to find that many of his bees were missing. The number of bees in hives that were still inhabited had dropped greatly, these hives contained only the queen and some younger bees, though the colonies still had stored nectar, pollen, and many developing bees. The older foraging bees, who specialize on gathering nectar and pollen to feed the hive, had simply disappeared. Stranger yet, the wax- and honey-eating pests that usually infest empty honeycombs, wax moths and small hive beetles, were absent from the collapsed colonies. In the end only 9 of the original 400 colonies survived.
In the months following Hackenberg's somewhat mysterious loss, 23% of commercial beekeepers in the US experienced similar losses, with affected operations losing an average of 45% of their colonies. Beekeeping is not the idyllic endeavor than many envision – bees often suffer from viral, bacterial, and fungal infections in addition to parasitic mites and insecticides – so beekeepers are accustomed to losing bees and colonies. Prior to 2006, according to a survey conducted by the Apiary Inspectors of America, beekeepers lost an average of 17% of their colonies each year due to various causes. But in the winter of 2007 the loss of colonies was more serious and more sudden and the cause of loss more mysterious than anyone had seen before. The term "colony collapse disorder" was coined to describe the sudden disappearance of foraging bees leading to the eventual demise of whole colonies.
Soon beekeepers, beekeeping organizations and university and government researchers began to search for the cause of colony collapse. Many hypotheses of varying likelihood have been floated, some of which garnered attention from the popular media. New honey bee diseases, genetically modified crops, global warming, sunspot activity and cell phones have all been suggested as cause for the bees' sudden disappearance. The most likely explanation is that colony collapse is the product of several different problems that simultaneously affect bee colonies.
Frames taken from colonies suffering from colony collapse disorder have few bees, but large numbers of developing larval and pupal bees. Compare with a frame full of bees taken from a healthy colony. Photos: Keith Delaplane from Oldroyd, 2007 and Reed Johnson
While the cause of colony collapse continues to be mysterious, it is possible that a newly introduced disease is contributing to the bees' demise. Using methods originally developed for the identification of new human diseases, the Israeli Acute Paralysis Virus (IAPV) was identified in the few bees remaining in colonies experiencing colony collapse. IAPV was first discovered in honey bees in Israel, where it causes bees to "shiver" their wings, then become paralyzed and die outside the hive. Despite the fact that most collapsing colonies in this study tested positive for IAPV, the sick bees did not display "shivering" and no dead bees were observed in front of hives.
The connection between IAPV and CCD has recently become less clear. Researchers have found IAPV in healthy colonies as well as frozen bee samples from as far back as 2002.
Varroa mites (Varroa destructor) are parasitic mites that survive by sucking the blood from honey bees. The mites can suck from any bee, but they target the pupal bees that are sealed inside a wax cell as the bees develop from a larva to an adult bee. A pupa that is fed on by mites will either die or develop into a severely weakened adult. Honey bee colonies with large mite infestations will be so weakened that the entire colony will eventually die out. Varroa mites are also capable of transmitting viruses that cause bee diseases and likely play a role in the transmission of the Israeli acute paralysis virus, a possible contributor to colony collapse disorder.
Varroa mites have not always been a problem in the U.S. Originating in southeast Asia, the mites do relatively little harm to honey bees native to the region. Over the last century they have been slowly moving westward into Europe and finally arrived in North America in the 1980's. The damage caused by varroa mites has been devastating to honey bees, decimating wild colonies, and making the business of beekeeping considerably more difficult.
Nosema apis is a single-celled parasite of honey bees that causes a condition sometimes called "bee dysentery". Nosema only affects adult bees, where it interferes with the digestion of pollen. Bees with Nosema apis have diarrhea-like symptons, with sick bees leaving distinctive yellow stripes on the outside of the hive. Bees infected with Nosema apis collect less pollen and nectar for the colony and die at a younger age. If many bees in a colony are infected with Nosema apis the colony will be weakend and will probably die.
Recently an Asian type of nosema, Nosema ceranae, has been discovered in the U.S. Though Nosema ceranae is indistinguishable from the old variety with the naked eye, it has been reported to cause symptoms in bees different from Nosema apis and more similar to colony collapse disorder. However, there is no evidence that this newly introduced Asian nosema contributes significantly to a hive's risk for colony collapse disorder.
A type of nosema, Nosema bombi, also affects bumble bees and may be harming their populations.
Pesticides, particularly a new class of pesticides similar to nicotine, called neonicotinoids, have been suspected as a contributor to colony collapse disorder. These nicotine-like insecticides are particularly problematic because they are "systemic" pesticides that get into all tissues of the plant – including the nectar and pollen that bees collect.
The effect of nicotine on human behavior is well known, but it has also been shown that low doses of nicotine-like pesticides can cause changes in the behavior of bees – particularly learning problems in honey bees. The failure of foraging bees to return to the the hive, the hallmark of colony collapse disorder, could be the result of bees' failure to learn the route home.
So far there has been no clear evidence that any pesticide is causing colony collapse disorder, but it is possible that pesticide exposure, combined with diseases or other factors, is contributing to the collapse of colonies.
Learning about bees and contributing your sightings to the BeeSpotter website are a great first step. While research into the causes of colony collapse disorder continues, there are some simple things you can do to help the bees in your neighborhood.
Plant a bee garden. And avoid mowing flowering weeds. It should come as
no surprise that well-fed bees are generally healthier bees. There
are some indications that colony collapse disorder is triggered by a
lack of good pollen and nectar. By planting a variety of flowers
that bees visit you can provide food to keep your local bees strong.
Flowering weeds provide an important source of nectar for honey bees and bumble bees Putting off mowing until weeds are finished
flowering can provide a needed source of food for
BeeSpotter Topic: Designing a Bee Garden
Minimize the use of pesticides. Most pesticides will kill bees right along with pest insects. It is especially critical to avoid spraying flowers during the day while bees are actively visiting. Even low doses of some pesticides, while they may not kill bees outright, can cause behavioral changes in bees and may contribute to colony collapse disorder.
Buy honey from a local beekeeper. Many beekeepers are struggling from the loss of bees to colony collapse disorder as well as losses from the range of other problems that affect modern beekeeping. By supporting your local beekeeper you're also supporting your local honey bees. Find local honey through the National Honey Board's Honey Locator.
To learn the latest news about colony collapse disorder visit the Mid-Atlantic Apiculture Research and Extension website: http://www.ento.psu.edu/MAAREC/ColonyCollapseDisorder.html.
Cox-Foster D., et al. 2007. A Metagenomic Survey of Microbes in Honey Bee Colony Collapse Disorder. Science 318: 283-287. [abstract]
Engelsdorp D., Underwood R., Caron D. and Hayes J. 2007. An Estimate of Managed Colony Losses in the Winter of 20062007: A Report Commissioned by the Apiary Inspectors of America. American Bee Journal. 147: 599-603. [pdf]
Chen, Y. and Evans, J.D. 2007. Historical Presence of Israeli Acute Paralysis Virus in the United States. American Bee Journal. [pdf]
Oldroyd, B.P. 2007. What's Killing American Honey Bees? PLoS Biology. 5(6): e168. [full paper]
Last updated: January 9, 2008