Hive Scourge? Virus linked to recent honeybee die-off

A little-known virus has been tagged as a suspect, or maybe just an opportunistic marker of disease, in the recent unexplained disappearances of honeybees.

CARRIER? U.S. honeybees have been plagued by the varroa mite (dark, rounded parasite on this bee’s back) which spreads and aggravates diseases, possibly including Israeli acute paralysis. USDA

During the past year, an estimated 23 percent of U.S. beekeeping operations saw worker bees vanish over the course of a few weeks for no obvious reason, a phenomenon dubbed colony-collapse disorder (SN: 7/28/07, p. 56).

Now, a massive genetic analysis of bees and the organisms that live in their bodies suggests a tie to Israeli acute-paralysis virus (IAPV), says Diana Cox-Foster of Pennsylvania State University in University Park. IAPV was detected in 83 percent of samples of bees from faltering colonies but in only 5 percent of samples from colonies without symptoms, she and her colleagues report online and in an upcoming issue of Science.

Researchers in Israel first described the fatal bee virus in 2004, but until now it hadn’t attracted wide attention. The lab analysis that has highlighted it, developed by Ian Lipkin of Columbia University, determines the genetic sequences of all creatures present in samples of both sick and healthy organisms. Then researchers look for DNA unique to the sick samples.

The bee analysis included two fungi that have been suspects in colony collapses. Nosema ceranae and Nosema apis occurred in 90 percent and 100 percent, respectively, of samples of sick colonies, says the Lipkin team, but also in 72 percent and 92 percent, respectively, of symptomfree colonies.

Researchers haven’t yet tested whether IAPV meets the standard requirements, called Koch’s postulates, that would define it as the cause of colony-collapse disorder. This test requires such steps as administering the supposed pathogen to test subjects, seeing whether they get the predicted disease, and recapturing the same pathogen from them.

Cox-Foster says that she and U.S. Department of Agriculture researchers are planning a version of the test, but it’s not going to be easy in this case. For one thing, she suspects that bees become susceptible to the virus only when weakened by some other factor, such as pesticide exposure.

Whether IAPV contributes to colony collapse or just shows up as a consistent indicator, “both would be good news,” says bee geneticist Gene Robinson of the University of Illinois at Urbana-Champaign. Such a marker would improve researchers’ ability to screen colonies for disease.

“This is the first record of the virus in North America,” says Cox-Foster, although she adds that no one has looked for it outside Israel. She and her colleagues have found IAPV in live bees from two suppliers in Australia and in packages of royal jelly, bee food for larvae destined to be queens, exported from China.

The question of the virus’ source could fuel debate over the rules for import and export of bees and bee products. In 2004, the first large-scale bee imports came from Australia. The United States also allows imports from New Zealand and Canada. At the time, the American Beekeeping Federation, based in Jesup, Ga., argued unsuccessfully for a quarantine system, says its executive director, Troy Fore.

He says that if imported IAPV were the only cause of the disease, he would have expected the path of infection across the United States to have been more straightforward. “If they tell us it’s a virus, there will still be more questions than answers,” he says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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