Focus: Declining Pollinators
A Stinging Issue: Declining Pollinator Populations
By Michele Arduengo, Ph.D.
Promega Corporation
Published in October 2007
A Story“I’ll be with you in apple blossom time “Momma, what’s apple blossom time?” “Well, not too long ago apples grew on trees.” “Apples grew on trees?!?” her daughter’s eyes grew wide. “Yes, there were no synthetic apples then. Farmers grew apple trees in huge areas called orchards, and every spring all of the apple trees would be covered in beautiful white flowers.” “There were flowers on trees?” her eyes grew even wider. “Yes, and you could smell the sweet smell drifting on the breeze and hear the hum of hundreds of bees busily collecting nectar from the blossoms. It was a beautiful sight.” “Why did we stop growing apples on trees?” “We didn’t want to, but all of the bees disappeared.” |
The Declining Honey Bee Population
Approximately one-third of food crops in the United States depend on animal pollination, and 80% of that pollination is the responsibility of commercial honey bees. These crops include apples, blueberries, cranberries, almonds and pears—an estimated 14 billion dollars of agricultural products for the United States alone (2).
When was the last time you saw a honeybee in your garden? Bumblebees and carpenter bees still visit the neighborhood patch, but the wild honeybee has been decimated by overuse of pesticides, loss of habitat and mite infestations. Evidence suggests that the wild honeybee populations in the United States have been virtually eliminated in some areas of the country, and scientists predict that the managed honeybee may disappear by 2035 (3).
Commercial bee operations are at risk too. In the fall of 2006, commercial beekeepers began reporting a mysterious phenomenon called colony collapse disorder (CCD). The beekeepers would open their hives and be greeted by silence—all of the worker bees had disappeared. CCD affected nearly 25% of professional beekeepers in the United States with some beekeepers losing up to 90% of their hives (4). The losses were so dramatic that two bills, the Pollinator Protection Act of 2007 and the Pollinator Habitat Protection Act, were proposed in the Senate (5). CCD is not limited to the United States;l occurrences have been reported in Germany, Switzerland, Sweden, Italy and Greece (6). At first some experts denied that CCD was any different from already noted diseases of bees and other pollinators, and other people blamed CCD on cell phone use, global climate change and genetically engineered plants. To date, nobody really knows what causes CCD, but most researchers agree that CCD probably is a consequence of several different factors. Hives decimated by CCD can be gamma irradiated to sterilize them and then successfully repopulated with new colonies; this result indicates that some kind of infectious agent or agents may be responsible for CCD (7). Since 18 honeybee viruses have been identified so far (8), determining which pathogen or combination of pathogens is involved in CCD is not a trivial task.
A Potential Marker for At-Risk Hives
Early in September 2007, a team of researchers from The Pennsylvania State University, Columbia University, the University of Arizona, 454 Life Sciences and the USDA Agricultural Research Service identified a potential marker of hives that may be destined for CCD. The recent completion of the honeybee genome sequence allowed scientists to use a metagenomic screen to compare hives that had succumbed to CCD and healthy “control” hives (4,5). Specifically, the group compared the genetic information of pathogens (viruses, mites, bacteria) present in the hives.
Both healthy and CCD colonies contained a host of pathogens, but CCD colonies tended to have more pathogens associated with them, and one virus, the Israel Acute Paralysis Virus (IAPV), had a statistically significant association with the CCD colonies. Only one of 26 healthy hives had IAPV, while 25 of the 30 CCD colonies were positive for IAPV. IAPV is particularly prevalent in Australia, where it does not seem to cause disease in honeybees. Researchers suggest that IAPV may be a consequence, rather than a cause, of CCD in US hives or that IAPV does not lead to problems unless it occurs in conjunction with other specific honeybee pathogens such as the varroa mite (4). The varroa mite is a vector for the Kashmir bee virus (KBV) and the sacbrood virus (SBV), and hives suffering from mite infestations may also be weakened to the point that they are more susceptible to SBV and KBV (8). A similar relationship may exist between mite infestation, IAPV and CCD.
Commercial honeybee colonies are transported between the coasts of the United States in order to provide bees for the pollination seasons for specific crops. In fact, the migration of bees into California via tractor trailers for almond pollination season is unofficially described as the largest bee migration in the United States. CCD was found mostly in these commercial migratory colonies. Possibly the long transport and limited food supply during transport predispose these colonies to pathogen attack.
Summary
As devastating as CCD is, it is not the entire story of bee decline. A host of factors including mite infestation and habitat destruction contribute to the demise of bee pollinators. The creation of ultra-large, weed-free farms has destroyed natural habitat. The introduction of invasive species like fire ants and the African hive beetle have damaged populations as well. The bumblebee is affected by pesticides applied to cotton fields when the bees are foraging, and aerial spraying for pests such as mosquitoes, gypsy moths and med-flies results in collateral damage to pollinator populations.
So while the news of a viral marker for CCD provides a useful research tool for discovering the cause of and combating this one issue, more hard work remains if we are to help these buzzing pollinators regain their foothold in ecosystems worldwide.
References
- Fleeson, N. and Von Tilzer, A. (1920) In Apple Blossom Time.
- Presto, G. (2007) Crops—and our wallets—may get stung by bee problems. Market Watch. [ http://www.marketwatch.com/news} ] Accessed 9/11/2007.
- Berenbaum, May R. (2007) Colony collapse disorder and pollinator decline. Testimony to 110th Congress, First Session. March 29, 2007. [http://www7.nationalacademies.org ] Accessed 9/11/2007.
- Stokstad, E. (2007) Puzzling decline of U.S. bees linked to virus from Australia. Science. 317, 1304–5.
- (2007) Senator Clinton co-sponsors bills to address decline of honey bee population. Web site of Senator Hillary Rodham Clinton. [http://www.senate.gov/~clinton/news/statements/record.cfm?id=277839 ] Accessed 9/11/2007.
- Shreeve, J.L. (2007) Bee decline threatens our dinner and countryside. Telegraph.CO.UK [http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/08/03/eabees103.xml] Accessed 9/11/2007.
- Cox-Forster, D.L. et al. (2007) A metagenomic of microbes in honey bee colony collapse disorder (abstract). Science. ePub ahead of print. [http://www.ncbi.nlm.nih.gov/sites/entrez] Accessed 9/11/2007.
- Shen, M. et al. (2005) Intricate transmission routes and interaction between picorna-like viruses (Kashmir bee virus and sacbrood virus) with the honeybee host and parasitic varroa mite. J. Gen. Virol. 86, 2281–9.
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