Honeybees could be on their way back, according to a new federal report.
The collapse of bee populations around the country in recent years has led to warnings of a crisis in foods grown with the help of pollination. Over the past eight years, beekeepers have reported losses over the winter of nearly 30 percent of their bees on average.
The new survey, published Thursday, found that the loss of managed honeybee colonies from all causes has dropped to 23.2 percent nationwide over the winter that just ended, down from 30.5 percent the year before. Losses reported by some individual beekeepers were even higher. Colony losses reached a peak of 36 percent in 2007 to 2008.
The survey of thousands of beekeepers was conducted by the Department of Agriculture and the Bee Informed Partnership, an organization that studies apian health and management.
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“It’s better than some of the years we’ve suffered,” said Dennis vanEngelsdorp, a director of the partnership and an entomologist at the University of Maryland. Still, he noted, a 23 percent loss “is not a good number.” He continued, “We’ve gone from horrible to bad.”
He said there was no way to say at this point why the bees did better this year.
Jeff Pettis, the co-author of the survey who heads the federal government’s bee research laboratory in Beltsville, Md., warned that “one year does not make a trend.”
A prominent environmental group found “an urgent need for action” in the new report. Lisa Archer, director the food and technology program for the organization Friends of the Earth, said, “These dire honey bee numbers add to a consistent pattern of unsustainable bee losses in recent years.”
While much attention has been paid to colony collapse disorder, in which masses of bees disappear from hives, that phenomenon has not been encountered in the field in the past three years, vanEngelsdorp said. Instead, what has emerged is a complex set of pressures on managed and wild bee populations that includes disease, a parasite known as the varroa mite, pesticides, extreme weather and poor nutrition tied to a loss of forage plants.
Treating colonies for the varroa mite, an Asian parasite that first reached the United States in 1987, seems to have the most direct effect on stemming losses, vanEngelsdorp said.
“The beekeepers that are treating for varroa mites lose significantly fewer colonies than beekeepers that are not treating colonies for varroa mites,” and those who treat them four or five times a year do better than those who only treat them once or twice, he said.
The new report will not satisfy those who argue that the loss of bees can be traced to a class of pesticides known as neonicotinoids, especially one manufactured by Bayer.
Those views are supported by papers such as one published this month in the journal Bulletin of Insectology that found that 6 of 12 previously healthy colonies exposed to the pesticides died and all exhibited symptoms of colony collapse disorder in the winter.
Bayer attacked that study, saying that the lead author, Chensheng Lu of the Harvard School of Public Health, “greatly misdiagnosed colony collapse disorder” in the colonies he studied, and that he used dosages of the pesticide 10 times greater than what bees might encounter in the wild.
In an interview, Lu said Bayer should reveal what it believes an “environmentally relevant” level of the pesticide should be.
VanEngelsdorp said Lu and his colleagues gave the bees doses far beyond what they would encounter in nature, and over longer periods of time, so the new study only shows that “high doses of ‘neonics’ kill bees — which is not surprising.”
Rather than looking for a single chemical or class of chemicals, Pettis said, it is important to assess the interplay of parasites, illness, food sources and pesticides. “Nobody likes that kind of complicated story, but year to year, all those factors could play into colony health,” he added.
Eric Mussen of the University of California, Davis, said colony collapse disorder and other pressures have made beekeepers focus more intently on maintenance of their colonies than in the past.
“People are being forced now to look more carefully at their bees,” he said. “If you don’t take care of them, you lose them.”