Causes of Colony Collapse Disorder

Causes of Colony Collapse Disorder

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Colony Collapse Disorder (CCD) refers to a worldwide phenomenon in which bee populations, particularly honey bees, have been drastically reduced. Various instances of dwindling bee populations have been recorded at various times since the mid-1800s, but the current situation, first noted in late 2006, is more severe; some beekeepers report having lost 90 percent of their hives. And although various possible reasons have been pinpointed, there is as yet no general consensus.

One possible cause is malnutrition among bee colonies. In many surveys, beekeepers report a period of �extraordinary stress� in a colony prior to that colony dying off, possibly attributable to poor nutrition. Some blame the exclusive feeding of high-fructose corn syrup produced from genetically modified corn to bee colonies as a supplement to their winter stores of honey and pollen, arguing that genetically modified foods may not provide adequate nutrition. Others point to the practice of providing bees with a monoculture diet, as opposed to a varied diet. Often, bees are fed a single food during the winter (such as corn syrup), and these same bees then pollinate only a single crop during the summer months (such as almonds or cherries). A 2010 study found that bees who pollinated a variety of plant species tended to have healthier immune systems than bees limited to a single plant species. This loss of diversity, affiliated with the large-scale farming operations prevalent today, is harmful to bees� nutritional health.

Various pathogens are also identified as possible causes of CCD. Most often cited is the varroa mite, which infects bees with deformed wing virus, Israel acute paralysis virus, and other deadly viruses. These mites also tend to weaken bees� immune systems, leaving bees susceptible to other diseases. A great many hives that have died off in the past five years have been infested with varroa mites, though not all dying colonies contain these mites, so varroa mites are likely one among several causes of CCD.

Causes of Colony Collapse Disorder
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Because mites, and the viruses they carry, can be transferred from bee to bee and from hive to hive, mite infestations might be considered a sort of �contagious� disease, spreading among bee colonies. Whenever a bee colony dies, for whatever reason, nearby healthy colonies of bees will often enter the dying hive and make use of existing provisions there. If these healthy colonies in turn become sick and begin dying, that would suggest that the healthy colony �caught� the virus from contaminated provisions in the colony that they robbed. However, it has also been observed that CCD can spread among hives without newly infected colonies having robbed infected hives. More research into the relationship between mites, viruses, and the spread of CCD is needed. In any event, beekeepers can safely reuse hives and other equipment from colonies that have died off only if they first treat the empty hive with DNA-destroying radiation.

Another possible culprit is a unicellular parasite called nosema; in its dormant stage, this fungus lives as a spore that is resistant to temperature extremes, dehydration, and even freezing. Nosema has been a known killer of honey bees since well before 2006, when CCD was first identified, so if the fungus plays any role in CCD, it is likely in combination with other stress factors.

Pesticides — specifically, insecticides — are another possible cause of CCD. Several studies have been done and, although there are often no common environmental factors among unrelated outbreaks of CCD, bee colony losses were not being reported at all at organic beekeeping operations. A 2010 survey found nearly 100 different pesticides, in significant amounts, in samples of bee pollen. The survey concluded that the presence of these pesticides in the recorded amounts was sufficient to compromise the physical fitness of the bees, but not enough to kill them. As with the pathogens, further study is needed regarding how pesticides might work together with other stress factors to cause a bee colony to die off.

Some beekeeping practices may be responsible for weakening bee colonies. Many beekeepers make greater profits from migratory beekeeping than they do from harvesting honey and bee byproducts. In this practice, hives are rented out to farmers for short periods of time — sometimes just a few weeks — for crop pollination. Bee rental has become a critical part of agriculture in California and elsewhere in the United States; with the large-scale farming done in these areas, native pollinators are not sufficient to get the job done. However, the spread of mites, viruses, and other pathogens is facilitated when migratory bees mingle with bees who have been rented from other beekeepers, or with native bees. Additionally, the constant movement and resettlement can bring trauma upon a colony, disrupting hive routines and possibly rendering the hive less resistant to infections and other disorders.

Electromagnetic radiation is yet another possible cause of CCN that is often mentioned in online discussions and in the media. It has been established that honey bees are capable of detecting weak static and low-frequency magnetic fields, in fact using such clues in navigation. However, there is as yet no evidence that bees are affected when they fly through microwaves associated with ground-based microwave receiving stations. Some have implicated the exponential increase in cell phone usage as a factor in CCD, although again, no actual research has suggested a connection. In an April 2011 study, a researcher placed cell phones directly inside several hives and noted increased instances of worker bees �piping� — announcing a swarming or signaling a disturbance to the colony. However, such piping is normal when bees sense a potential threat to the hive and is not in itself damaging to the colony, any more than a routine fire drill would be to a busy office building.

Colony collapse disorder is a very real phenomenon, with as yet unknown long-term consequences. Likewise, the causes have not been identified with any precision. It is likely that a variety of stress factors working in tandem have combined to cause these drastic falloffs in bee populations.