发布时间：2016-08-11 来源：新东方在线 发布人：too
When honey bees began to desert their hives recently, never to return, it threw apiarists into a panic. What appeared to be perfectly healthy adult bees would flee their queen, the young and their foodstores. Instead of ransacking the empty hive, other bees would avoid it like the plague. Yet there was nothing obviously wrong. Researchers have now identified the first tangible clue in the mystery—a relatively new virus.
Colony collapse disorder became widespread in America in the winter of 2006-07, when about a quarter of the nation's beekeepers were affected, each losing between 30% and 90% of their winged workers. Bees are valued not so much for their honey, which is worth some $200m a year in America, but for their work in pollinating crops. This brings the economy some $15 billion a year, as apiarists move their hives to land producing fruit, vegetables and nuts.
Finding exactly why colonies collapse has been taxing the minds of both federal and university scientists. There have been few bodies on which to conduct autopsies. Those adult bees that have been found dead near an abandoned hive have been riddled with almost every bee disease known to man. Now a report by Diana Cox-Foster of Pennsylvania State University and her colleagues, published in the September 6th issue of Science, points the finger at the Israeli acute paralysis virus. The lurgy in question was, the researchers suggest, imported from Australia.
Because many factors could be acting together to cause bee colonies to collapse, Dr Cox-Foster and her colleagues decided to examine everything they could find within the empty hives. They collected samples from infected hives and compared them not only with samples from apparently healthy hives but also with an analysis of royal jelly—a bee secretion fed to the larvae—from China, which has not been affected by the mystery disorder. From their samples, the researchers extracted RNA—a chemical that carries and helps to decode genetic information. Their analysis revealed the presence of various bacteria, fungi and viruses that were lurking in the hives and the royal jelly. They then looked to see whether there was anything in the abandoned hives that was not found elsewhere.
What they found was a virus first identified in 2004 in the Middle East. Bees infected with Israeli acute paralysis virus shiver, their bodies become frozen and they die. But the virus itself cannot be the sole cause of colony collapse disorder. For a start, all the hives infected with it were also infested with a second nasty, the Kashmiri bee virus. Yet this virus was also present in many of the apparently healthy hives. Intriguingly, there was also a virus that the researchers were unable to classify. They suspect it may be a new lineage of the Kashmiri bee virus, but it could be something completely novel. This second virus was also found only in the abandoned hives.
The researchers reckon that the reason why so many honey bees are dying is down to a combination of factors that are found only, so far, in America. The Israeli acute paralysis virus may have had such a devastating effect there because of the presence of a parasite called the varroa mite. This parasite weakens the immune systems of bees, making the consequences of an infection more likely to be fatal. Tellingly, bees in Australia have not been infected by the parasite.