“Globalization clearly has had impacts on emerging and re-emerging infectious diseases of humans,” said Dr. Berenbaum. “Should bees be any different?

Dr. Pettis said that even if the virus is involved, it is likely that more than one factor has to align for a hive to collapse, with another possible influence being poor nutrition. Most of the colonies that had big losses over last winter were in areas that experienced drought a few months beforehand, and thus a lack of nectar in flowers, he said.

Another factor, he said, could be the stress that comes from the increasingly industrial-style beekeeping operations in the United States, in which truckloads of hives crisscross the country to pollinate California almonds or Florida orchards each season.

But the virus stands out as a top suspect. While seven viruses and a host of bacteria and parasites were identified in the genetic screening, only the Israeli bee virus, first identified in 2004, was strongly tied to the samples taken from keepers who reported the collapse disorder.

While it was first identified by scientists in Israel, the virus appears to exist in many parts of the world, said W. Ian Lipkin, one of the authors of the new study and director of the Center for Infection and Immunology of Columbia University. When the group screened some samples of Chinese imports of a bee product called royal jelly, they found evidence of the virus, as well.

In Israel, it also seems to produce bee symptoms not reported in the United States, including shivering and a pattern of finding dead bees near hives.

Dr. Lipkin, whose focus is human disease, became involved because the quest for a cause for the beehive collapses employed new genetic sifting techniques that he said might also prove useful in investigating human disease outbreaks.