The mysterious disappearance of honeybees in America and other parts of the world could be explained by a virus which is transmitted by a parasitic mite, scientists believe.
The virus has been identified in commercial bee hives which suffered from colony collapse disorder (CCD) – when worker bees suddenly vanish without trace, leaving behind a queen bee and a store of pollen and honey. Although the link with the virus does not prove it causes CCD, experts think it plays a significant role, perhaps together with another, as yet unknown, agent.
The virus is transmitted by the varroa mite – a parasite first detected in 1992 in Britain, where it has caused extensive damage in its own right. It is feared that it could also become an agent for transmitting new viral infections. Honeybees are important throughout the world, not just for their honey but because many commercial fruit and vegetable crops rely on them for pollination. American bee-keepers have been hit hardest by CCD – with about a quarter reporting that between 50 per cent and 90 per cent of their hives are affected.
US scientists genetically analysed biological material found in affected and unaffected hives. They were able to eliminate all but one type of DNA – that belonging to a known bee pathogen called Israeli acute paralysis virus. This was first identified in 2002 at the Hebrew University of Jerusalem, as biologists investigated an outbreak of paralysis and death among Israeli bees. The US team believes the virus may have been introduced to America by bees imported from Australia.
"Our extensive study suggests the Israeli acute paralysis virus may be a potential cause of CCD," said Ian Lipkin, of Columbia University, a senior author of the study, which is published in the journal Science. " Our next step is to ascertain whether this virus, alone or in concert with other factors such as microbes, toxins and stressors, can induce CCD in healthy bees."
The scientists sequenced all the different DNA types found in the affected and unaffected hives. By a process of elimination, they were able to identify Israeli acute paralysis virus as the most likely culprit. It was found in more than 96 per cent of affected colonies but in almost none of the unaffected hives.
The team found bacterial DNA in the hives but these microbes belonged to species known to live harmlessly within a honeybee's gut, and so could be eliminated as a possible cause of CCD. They then turned to viruses. "We knew before we started that we would find a boatload of viruses in the bees, given our preliminary research," said researcher Diane Cox-Foster, a professor of entomology at Penn State University. "Eighteen different types are known from serology and antibody work in England." The experts analysed DNA from 21 healthy colonies and 30 affected by CCD and concluded that the increased risk of the disorder depended on levels of infection with the Israeli virus. The prevalence of the virus and its timing with CCD outbreaks suggested it was a "significant marker", Ms Cox-Foster added.
- Bees are essential for food production. Without them, nearly 100 major crops worldwide would not be pollinated and would not set fruit.
- In the US alone, honeybees pollinate crops worth more than an estimated £7bn.
- Colony collapse disorder was first identified in the US in 2005 but there have also been reports of mysterious disappearances of bees in Brazil and European countries including Britain, where it is known as " the Mary Celeste phenomenon".
- Various causes have been suggested, ranging from pesticide and agro-chemical use to malnutrition and mobile phones, which cause electromagnetic interference with a bee's navigation system.