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Thread: Are mobile phones wiping out our bees?

  1. #11
    There is no agreement on the causes. Wise.

    What's Killing American Honey Bees?

    Benjamin P. Oldroyd

    Funding. The author received no specific funding for this study.

    Competing interests. The author has declared that no competing interests exist.

    Citation: Oldroyd BP (2007) What's Killing American Honey Bees? PLoS Biol 5(6): e168 doi:10.1371/journal.pbio.0050168

    Published: June 12, 2007

    Copyright: © 2007 Benjamin P. Oldroyd. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

    Abbreviations: CCD, colony collapse disorder; GM, genetically modified

    Dr. Benjamin P. Oldroyd is with the Behaviour and Genetics of Social Insects Laboratory, School of Biological Sciences, University of Sydney, New South Wales, Australia. E-mail:

    On February 22, 2007, many Americans woke up to media reports that something was awry with their honey bees. A significant proportion of American beekeepers were complaining of unusually high rates of colony loss as their bees broke from their overwintering clusters. Loss of some colonies (say 10%) in early spring is normal and occurs every year. In 2007, however, losses were particularly heavy and widespread—beekeepers in 22 states (including Hawaii) reported the problem. Some beekeepers lost nearly all of their colonies. And the problem is not just in the United States. Many European beekeepers complain of the same problem. Moreover, beekeepers and researchers do not understand the specific causes of the losses.
    Is There a Real Problem?

    Were the losses in 2007 within the normal range, or is there something new afoot in the bee industry? If there is something new, what is it? Is it indicative of a general toxic overload of agricultural ecosystems, or a problem confined to the bee industry? Should beekeepers be worried? Should we be worried? The US House Agriculture Committee is sufficiently worried to be holding hearings into the matter, as well they might. Honey bees are essential pollinators: in 2000, the value of American crops pollinated by bees was estimated to be $14.6 billion [1].

    The syndrome is mysterious in that the main symptom is simply a low number of adult bees in the hive. . . There are no bodies, and although there are often many disease organisms present, no outward signs of disease, pests, or parasites exist.

    Here, I try to get to the bottom of the unsolved mystery of colony collapse disorder (CCD)—the official description of a syndrome in which many bee colonies died in the winter and spring of 2006–2007.
    What is CCD?

    The syndrome is mysterious in that the main symptom is simply a low number of adult bees in the hive. (This is a bit like going to a previously well-populated hen house and finding hardly any hens.) There are no bodies, and although there are often many disease organisms present, no outward signs of disease, pests, or parasites exist. Often there is still food in the hive, and immature bees (brood) are present. The cause of the loss of bees seems to be the sudden early death, in the field, of large numbers of adult workers [2]. Curiously, the dead colonies tend to be left alone by the two cleptoparasites that normally infest dead honey bee colonies: the wax moth Gallaria mellonella and the small hive beetle Aethina tumida. Could this be due to some toxic residue in the dead colonies? Perhaps this was a contributing factor, but more likely the time of year meant that there were few cleptoparasites about—their abundance is seasonal.
    Figure 1. A Colony of Honey Bees Affected by CCD

    Note the small number of adult workers relative to the large amount of brood.

    (Photo: Keith Delaplane)
    Were the Losses Unusual?

    Some winter losses are normal, and because the proportion of colonies dying varies enormously from year to year, it is difficult to say when a crisis is occurring and when losses are part of the normal continuum. What is clear is that about one year in ten, apiarists suffer unusually heavy colony losses. This has been going on for a long time. In Ireland, there was a “great mortality of bees” in 950, and again in 992 and 1443 [3]. One of the most famous events was in the spring of 1906, when most beekeepers on the Isle of Wight (United Kingdom) lost all of their colonies [4]. American beekeepers also suffer heavy losses periodically. In 1903, in the Cache valley of Utah, 2000 colonies were lost to a mysterious “disappearing disease” following a “hard winter and cold spring” [5]. More recently, there was an incident in 1995 in which Pennsylvania beekeepers lost 53% of colonies [6].

    Often terms such as “disappearing disease” or “spring dwindling” are used to describe the syndrome in which large numbers of colonies die in spring due to a lack of adult bees [7,8,9]. However in 2007, some beekeepers experienced 80–100% losses. This is certainly the extreme end of a continuum, so perhaps there is indeed some new factor in play.
    What Are the Possible Causes?
    Diseases and parasites

    Honey bees are affected by a large number of parasites and pathogens. Mostly these have a set of well-defined symptoms that do not relate to CCD. For example, there are two major bacterial diseases that affect the brood: European Foul Brood (caused by Mellisococcus pluton [10]), and American Foul Brood (caused by Paenibacillus larvae [11]). There is also a fungal disease of the brood Ascosphaera apis [12]. These organisms have no effect on adult bees but have distinctive symptoms in larvae and pupae.

    The parasitic mite Varroa destructor infests brood cells and lives phoretically on adult bees [13]. But heavy mite infections are obvious to professional beekeepers, especially by the stage where colonies are dying of the infestation. So in itself, Varroa infestation is unlikely to cause CCD.

    A Tarsonemid mite Acarapis woodi can infest the trachea of adult bees [14] and is now widespread in North America. Acarapis infections were once thought to be the cause of the famous Isle of Wight disease, with symptoms like CCD. However, eminent honey bee pathologist L. Bailey is extremely sceptical that Isle of Wight disease has anything to do with an infectious agent [15]. This is not to say that the Isle of Wight disease is the same as CCD, nor does it exclude the possibility that Acarapis may contribute to CCD.

    A protozoan, Nosema apis, infests the guts of adult bees, and when present in high numbers, causes dysentery and early senescence of adult workers [16]. This is also unlikely to be the direct cause of CCD, because the dysentery is obvious and because just about all honey bee colonies are chronically infected with the parasite every spring, even when there are no colony losses. In an interesting twist, however, a new Nosema species, N. cerana, has been recently identified from the Asian hive bee Apis cerana [17] and has now been found on A. mellifera in Europe [18–20]. This “new” pathogen has spread to the US and some researchers speculate that it has contributed to CCD.

    More likely to play a role in CCD are a variety of viruses that affect adult bees (Table 1). Most adult honey bees carry symptomless viral infections [21,22]. However, under conditions of stress caused by poor nutrition, inclement weather, or parasitism by V. destructor [23] or N. apis [24], viral populations can increase and cause symptoms in adult bees. The paralysis viruses cause adult bees to tremble and shake, crawling away from the nest unable to fly. Paralysis can certainly reduce the life expectancy of workers dramatically [25], and cause spring dwindling. But in the 2007 outbreak of CCD, there was no evidence of trembling distressed workers. Therefore, the paralysis viruses are not strong candidates for the causative agent of CCD.

  2. #12

    The Earth's Magnetic Field?

    I read somewhere that the cause of CCD might be a rapid change in the earth's magnetic field. From

    The Earth's magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate -- 10km per year at the beginning of the 20th century, up to 40km per year in 2003. It is also unknown if this drift will continue to accelerate.
    Whether or not this is the cause of CCD, there's no doubt that magnetic field fluctuations can affect animals that use the field for navigation. And unlike global warming, this is a problem we can't blame on ourselves!

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