The mysterious disappearance of droves of honeybees in the US may be due to an imported virus, suggests a new study.
Beekeepers have witnessed a dramatic drop in their bee numbers since autumn 2006, though some saw signs as far back as 2004. Now a genetic analysis of more than 50 honeybee colonies suggests that a virus called Israeli acute paralysis virus (IAPV) might be behind this bizarre phenomenon.
Experts say they have “circumstantial evidence” linking the arrival of honeybee imports from Australia with the emergence of IAPV in the States. First identified in Israel in 2004, IAPV causes bees to develop shivering wings and eventually become paralysed, leading to death just outside the hive.
Scientists are quick to add, however, that a great deal of research remains necessary to know whether the virus truly is to blame.
About 50% to 90% of commercial honeybee colonies in the US have suffered from colony collapse disorder (CCD) – a strange phenomenon in which entire bee populations disappear from a colony within a matter of days, sometimes leaving behind only the queen and a few stragglers. The bee die-off has sparked great concern as these insects play an essential role in the pollination of more than 90 fruit and vegetables worldwide. Experts place the value of these crops at $14.6 billion in the US alone.
In recent months entomologists have pointed to a wide range of potential explanations for CCD – blaming everything from heavy pesticide use, to genetically modified crops, and even radiation from mobile phones.
To help unravel the mystery, Jeffery Pettis at the Bee Research Laboratory of the US Department of Agriculture in Beltsville, Maryland and his collaborators collected genetic samples from 51 colonies across the US, 30 of which had been devastated by CCD.
By comparing the gene fragments they found against the recently published honeybee genome sequence, Pettis and his colleagues quickly spotted the presence of foreign DNA belonging to the Israeli acute paralysis virus.
Among all the pathogens they identified, only IAPV was tightly linked to colony collapse – the virus appeared in all of the 30 colonies devastated by CCD, but only one of the apparently healthy colonies.
Because the US started allowing bee imports from Australia in 2004 – around the time that bees started dying in the states – the scientists also tested the genes of apparently healthy bees imported from Australia as well. These tests identified the presence of IAPV in the Australian sample, hinting that the imports might be to blame.
The new insights into IAPV are “a step forward” according to Daniel Weaver, president of the American Beekeeping Federation.
For now, all researchers have is an association between the virus and CCD. Future experiments in the lab will prove whether it can in fact cause healthy bees to develop the bizarre hive-deserting behaviour seen in CCD.
Of the possible IAPV link, entomologist Greg Hunt at Purdue University in West Lafayette, Indiana, US, says, “At this point it’s still circumstantial evidence because their samples were from very sick bees.”
“I think we have new leads,” Pettis says of the bee disappearance. “I still believe multiple factors are involved in CCD.” He points out that the varroa mite, which is prevalent in the US, weakens the immune system of bees, perhaps making them susceptible to IAPV. This could also help explain why bees infected with IAPV in Australia where the mite is absent do not show as dramatic changes in their behaviour, say scientists.
The authors of the paper also note that the IAPV strain in the US might have a slightly different genetic sequence making it more virulent than the IAPV found elsewhere.
Scientists are consulting with the US Animal and Plant Health Inspection Service to determine whether the country should consider blocking honeybee imports from Australia that carry IAPV. And since Pettis and his colleagues found traces of IAPV in Chinese “royal jelly” – a type of honeybee secretion used to feed the insects – they are considering whether US beekeepers should cease using this foreign product too.