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Colony collapse disorder

Colony collapse disorder

Idea

Colony collapse disorder (CCD), also known as honey bee depopulation syndrome (HBDS), refers to a recent dramatic increase in the occurrences of almost all the worker bees disappearing from a bee colony, causing it to collapse.

Although such disappearances have been recorded throughout history, there appears to have been a huge increase in occurrences in North America and Northern Europe over the last two decades. As bees are the dominant pollinators for many natural plants and farmed crops, this issue may have wide import.

Details

The first scientific accounts of large scale colony collapse disorder date from the start of the 1990s, but the topic has been of high interest and impact to bee-keepers and environmental scientists from the 2005 onwards. This phenomenon is significant both because of the role of honey bees pollinating crops and the lack of understanding of its precise causes.

By 2001, 3 of 19 British species of bees had become extinct, and 9 more were critically endangered:

In 2002, Italian beekepers reported a 50% drop in honey production from previous years:

By 2006, bee populations in the US had dropped by half as compared to a half century ago:

  • Jeffrey Kluger and Kristina Dell, The buzz on bees, Time Magazine, October 29, 2006.

The same trends are happening elsewhere as well.

Roles of honey bees in pollination

The honey bee is the dominant means of pollination for many food crops and other plants in northern Europe, as well as being used to pollinate some “export crops” grown in other parts of the world.

Honey bees are not native to America, so in America it is crops of European extraction that require bee pollination. In 2000, the total U.S. crop value that was wholly dependent on honey bee pollination was estimated to exceed $15 billion. They are currently responsible for pollination of approximately one third of the United States’ crop species, including such species as almonds, peaches, soybeans, apples, pears, cherries, raspberries, blackberries, cranberries, watermelons, cantaloupes, cucumbers and strawberries.

There are claims that in the absence of bees, their role would be fully taken over by other pollinating insects. However, the feasibility of this is uncertain on the scale of large commercial farming.

The potential importance of CCD is highlighted by this quote from a Times article

Already, says Goulson, crop yields are beginning to suffer. Bald spots are appearing at the centres of bean fields where bumblebees are failing to penetrate. As in so many other aspects of global life, it is China that lights the way ahead. In Sichuan province, the most important crop is pears, which depend on pollination by bees. But there are no bees. A blunderbuss approach to pesticides has all but wiped them out. Result: thousands of villagers have to turn out with paintbrushes to pollinate the trees by hand. “It’s just about possible in a country where labour is cheap,” says Goulson, “but it wouldn’t work in Europe.”

Possible causes of CCD

There appears to be no conclusive single cause for CCD. Some of the suspected causes are:

  • Malnutrition This is hypothesised to be due to some aspect of diet, eg, farming monoculture, deliberate feeding with high-fructose corn syrup, micronutrient defeiciency, genetically modified crops.

  • Pathogens There are various suspect pathogens, eg, Varroa mites.

  • Pesticides There are various types of pesticides hypothesised to affect bee health.

  • Antibiotics and miticides Beekeepers, particularly commercial beekeepers, use various chemicals in an attempt to optimise the health and productivity of their bees, but some researchers suspect unintended results from these treatments.

  • Bee rentals and migratory beekeeping In America, there are virtually no feral bees and travelling bee hives cross the country, stopping temporarily when paid so that the bees will pollinate local crops. There is concern that this mobility leads to both stress on the bees and leads to much wider spread of infections and parasites amongst bee populations.

  • Climate change Environmental changes and stresses due to climate change may be a contributor.

  • Electromagnetic radiation It has been hypothesised that bees’ memory, navigation or general health can be affected by electromagnetic radiation, primarily from mobile phones and the cell towers. The primary evidence appears to be the correlation between mobile phone spread and CCD reports, with direct experiments appearing not to demonstrate significant effects on bees.

Some recent work suggests which of these causes are most important. For example, Bromenshenk et al. (see references below) found the combination of Nosema fungus and invertebrate iridescent virus to be dominant, although some concerns have been raised about this study. In general, scientific reports about CCD do not seem to agree over the globe, and there may be issues regarding methodology or conflicts interests, since of the researchers also work for pesticide companies.

Reaction: helping bees

People have reacted upon hearing the news of colony collapse disorder by taking measures to help bee populations. Beekeeping is becoming more popular, even in urban areas. It was recently made legal in New York City. People are also planting ‘bee-friendly’ gardens, with plants that attract bees, especially native species:

Questions

  1. What are the factors causing of CCD, and how do they interact to cause a full collapse? Are there important emergent phenomena causing this (that may have wider applicability)?

  2. Are there effective changes in human bee management that would improve the robustness of bee colonies? How much effect is the new popularity of beekeeping having, or the interest in bee-friendly gardening?

References

As always, it’s good to start with Wikipedia:

Also see:

This paper suggests an explanation of colony collapse disorder:

  • Jerry J. Bromenshenk, Colin B. Henderson, Charles H. Wick, Michael F. Stanford, Alan W. Zulich, Rabih E. Jabbour, Samir V. Deshpande, Patrick E. McCubbin, Robert A. Seccomb, Phillip M. Welch, Trevor Williams, David R. Firth, Evan Skowronsk, Margaret M. Lehmann, Shan L. Bilimoria, Joanna Gress, Kevin W. Wanner and Robert A. Cramer Jr, Iridovirus and Microsporidian Linked to Honey Bee Colony Decline, DOI: 10.1371/journal.pone.0013181, PLoS One, 2010.

Bromshenk et al. appear to suggest that while “traces” of pesticide are widespread, these don’t have any significant effect, saying: “A survey of bee samples from across the USA revealed traces of pesticides in many bee samples, but none were shown to correlate with CCD.” The survey they cite in support of this didn’t actually look for any correlation. Rather it suggested synergistic effects are a major factor, e.g.: “the potential for multiple pesticide interactions affecting bee health seems likely.”

  • Christopher A. Mullin, Maryann Frazier, James L. Frazier, Sara Ashcraft, Roger Simonds, Dennis vanEngelsdorp, Jeffery S. Pettis, High Levels of Miticides and Agrochemicals in North American Apiaries: Implications for Honey Bee Health, PLoS One 2010.

category: ecology