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10 Possible Causes of Colony Collapse Disorder

Theories Behind the Sudden Disappearance of Honeybee Hives

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In the fall of 2006, beekeepers in North America began reporting the disappearances of entire colonies of bees, seemingly overnight. In the U.S. alone, thousands of bee colonies were lost to Colony Collapse Disorder. Theories about the causes of Colony Collapse Disorder, or CCD, emerged almost as quickly as the bees disappeared. No single cause or definitive answer has yet been identified. Most researchers expect the answer to lie in a combination of contributing factors. Here are ten possible causes of Colony Collapse Disorder.

Published March 11, 2008

1. Malnutrition

Photo: © Whitney Cranshaw, Colorado State University, Bugwood.org
Wild honeybees forage on the diversity of flowers in their habitat, enjoying a variety of pollen and nectar sources. Honeybees used commercially limit their foraging to specific crops, such as almonds, blueberries, or cherries. Colonies kept by hobbyist beekeepers may fare no better, as suburban and urban neighborhoods offer limited plant diversity. Honeybees fed on single crops, or limited varieties of plants, may suffer nutritional deficiencies that stress their immune systems.

2. Pesticides

Photo: © Medioimages/Photodisc/Getty Images
Any disappearance of an insect species would implicate pesticide use as a potential cause, and CCD is no exception. Beekeepers are particularly concerned about a possible connection between Colony Collapse Disorder and neonicotinoids, or nicotine-based pesticides. One such pesticide, imidacloprid, is known to affect insects in ways similar to the symptoms of CCD. Identification of a causative pesticide will likely require studies of pesticide residues in the honey or pollen abandoned by affected colonies.

3. Genetically Modified Crops

Photo: © Doug Wilson, USDA Agricultural Research Service
Another suspect in the case is the pollen of genetically modified crops, specifically corn altered to produce Bt (Bacillus thuringiensis) toxin. Most researchers agree that exposure to Bt pollen alone is not a likely cause of Colony Collapse Disorder. Not all hives foraging on Bt pollen succumbed to CCD, and some CCD-impacted colonies never foraged near genetically modified crops. However, a possible link may exist between Bt and disappearing colonies when those bees had compromised health for other reasons. German researchers note a possible correlation between exposure to Bt pollen and compromised immunity to the fungus Nosema.

4. Migratory Beekeeping

Photo: © Kent Knudson/PhotoLink/Getty Images
Commercial beekeepers rent their hives to farmers, earning more from pollination services than they could ever make from honey production alone. Hives are stacked on the back of tractor trailers, covered, and driven thousands of miles. For honeybees, orientation to their hive is vital to life, and being relocated every few months must be stressful. Additionally, moving hives around the country may spread diseases and pathogens as honeybees intermingle in the fields.

5. Lack of Genetic Biodiversity

Photo: © Carl Dennis, Auburn University, Bugwood.org
Nearly all queen bees in the U.S., and subsequently all honeybees, descend from one of several hundred breeder queens. This limited genetic pool may degrade the quality of queen bees used to start new hives, and result in honeybees that are significantly more susceptible to diseases and pests.

6. Beekeeping Practices

Photo: © Whitney Cranshaw, Colorado State University, Bugwood.org
Studies of how beekeepers manage their bees may determine trends that lead up to the disappearance of colonies. How and what bees are fed would certainly impact their health directly. Splitting or combining hives, applying chemical miticides, or administering antibiotics are all practices worthy of study. Few beekeepers or researchers believe these practices, some of which are centuries old, are the single answer to CCD. These stresses on the bees could be contributing factors, however, and require closer review.

7. Parasites and Pathogens

Photo: © Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Known honeybee pests, such as American foulbrood and tracheal mites, do not lead to Colony Collapse Disorder on their own, but some suspect they may make bees more susceptible to it. Beekeepers fear varroa mites the most, because they transmit viruses in addition to the direct damage they do as a parasite. The chemicals used to control varroa mites further compromise the honeybees' health. The answer to the CCD puzzle might lie in the discovery of a new, unidentified pest or pathogen. For example, researchers discovered a new species of Nosema in 2006; Nosema ceranae was present in the digestive tracts of some colonies with symptoms of CCD.

8. Toxins in the Environment

Photo: © Kim Steele/Getty Images
Honeybee exposure to toxins in the environment warrants research as well, and some suspect chemicals as a cause of Colony Collapse Disorder. Water sources may be treated to control other insects, or contain chemical residues from runoff. Foraging bees might be impacted by household or industrial chemicals, through contact or inhalation. The possibilities for toxic exposure make pinpointing a definitive cause difficult, but this theory requires attention by scientists.

9. Electromagnetic Radiation

Photo: © Arthur S. Aubry/Getty Images
A widely-reported theory that cell phones may be to blame for Colony Collapse Disorder proved to be an inaccurate representation of a research study conducted in Germany. Scientists looked for a link between honeybee behavior and close-range electromagnetic fields. They concluded there is no correlation between the inability of bees to return to their hives and exposure to such radio frequencies. The scientists vehemently disavowed any suggestion that cell phones or cell towers are responsible for CCD.

10. Climate Change

Photo: © Martin Child/Getty Images
Rising global temperatures cause a chain reaction through the ecosystem. Erratic weather patterns lead to unusually warm winters, drought, and floods, all of which affect flowering plants. Plants may blossom early, before honeybees can fly, or may not produce flowers at all, limiting nectar and pollen supplies. Some beekeepers believe global warming is to blame, if only in part, for Colony Collapse Disorder.
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