Unexplained honeybee deaths have recently started showing up in Florida, the same state where the mysterious Colony Collapse Disorder was first discovered a year ago, the Agriculture Department's top bee scientist said Thursday.

Jeffrey Pettis, research leader of the department's Bee Research Laboratory in Beltsville, Md., said it is too early to say if another round of bee die-offs has started.

The insect plague devastated thousands of commercial bee hives in several states last year, posing a threat to crops that depend on bees for pollination.

When it occurs, worker bees fail to return to hives, leaving juvenile bees and some adults to die.

"We have heard recently from Florida beekeepers who have colonies in declining health," said Pettis.

Speaking at a conference on problems that confront honeybees, bumblebees, butterflies, birds and other important pollinators, Pettis said specimens have been brought to his lab for analysis.

Colony Collapse Disorder, known as CCD, was first reported by a Florida beekeeper in November of last year. It quickly started showing up in other states.

Pettis was a member of a team of government and university scientists who last month reported that a recently discovered bee virus had been linked to hives in which CCD had occurred, but not to healthy hives.

The virus, Israeli Acute Paralysis Virus, was first identified in 2004 by entomologists in Israel. In addition to bees from U.S. hives that appeared to have suffered from CCD, it was found in imported bees from Australia and royal jelly from China, the scientists said.

Pettis said the next step will be to attempt to induce the same condition by inoculating bees with the suspect virus.

He said Thursday that these experiments have not been completed, and that he could not predict when he would have results to actually determine whether the virus was the cause of last year's hive collapses.

The experiments will try to combine the inoculations with factors that scientists suspect might be depressing the insects' immune systems and making them more susceptible.

These factors include infestation by parasitic mites and exposure to insecticides, he said.

In a report issued last year before the appearance of CCD, the National Academy of Sciences warned that all pollinators are threatened by a variety of factors, including habitat loss and climate change.

Pollinators of all kinds are critical to more than $15 billion worth of agriculture products a year, the report stated.

The conference here was organized by the North American Pollinator Protection Campaign, a coalition of more than 100 government agencies, conservation organizations and universities in the United States, Mexico and Canada.

On the Web:

The North American Pollinator Protection Campaign: www.pollinators.org.