A virus linked to the strange disappearance of honeybees did not arrive in the United States via recently imported Australian hives, according to a new genetic analysis. Instead, the virus has been present here since at least 2001. "On the face of it, it seems to let the Australians off the hook," says entomologist Nicholas Calderone of Cornell University. But he and others stress that much remains to be learned before the role of the virus in colony collapse is clear.
One year ago, beekeepers across the country began to report that worker bees were inexplicably abandoning their hives and leaving the brood to die. Although firm statistics are hard to come by, so-called colony collapse disorder may have afflicted as many as 25% of U.S. beekeepers and perhaps others around the world. Possible culprits included pesticides, parasites, and chronic stress from poor nutrition and the long-distance truck rides that many commercial hives undergo (Science, 18 May, p. 970).
In September, a team of researchers reported that collapsed hives were much more likely than healthy hives to be infected with a virus called Israeli acute paralysis virus (IAPV) (Science, 7 September, p. 1304). What's more, IAPV seemed to have come from Australia. The virus was found in a sample of Aussie honeybees, which have been imported as of 2005, while bees collected in the United States in 2004 didn't seem to have the virus. This discovery worried beekeepers in Australia, who sell the bees, and farmers in the United States, who depend on imports to help pollinate the lucrative California almond crop.
Some experts questioned whether the team had looked at enough honeybees to rule out the possibility that IAPV wasn't already present in the United States before the Australian imports arrived. So virologist Yanping Chen and geneticist Jay Evans, both of the U.S. Department of Agriculture's Bee Research Laboratory in Beltsville, Maryland, headed to their freezers. They pulled out samples from two commercial beekeepers in Maryland, collected between 2001 and 2004, plus others collected in 2003 from California beekeepers. They also analyzed bees from Pennsylvania and Israel.
The virus turned up in samples dating back to 2002. It's probably been here even longer, Evans says, noting the variation in a highly conserved RNA region among West Coast and East Coast bees. The results will appear in the December issue of the American Bee Journal, a trade magazine. Evans says he and colleagues plan to see how IAPV from Australian bees compares to virus in the United States, but they need more samples.
Although it might seem that Australian bees didn't smuggle in a killer for the first time, Evans say IAPV may still play a role in disease. One possibility is that IAPV from Australia might be more virulent than homegrown varieties. But researchers don't yet know whether one variety of IAPV can be more harmful than another. For that matter, no one has yet shown that IAPV can cause colonies to collapse. "Until you have introduced the virus and caused disease, you're just postulating," cautions Bruce Webb, an entomologist at the University of Kentucky in Lexington. "The conclusive data are not in."