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Nearly one in three commercial honeybee colonies in the United States died or disappeared last winter, an unsustainable decline that threatens the nation's food supply.
Multiple factors -- pesticides, fungicides, parasites, viruses and malnutrition -- are believed to cause the losses, which were officially announced today by a consortium of academic researchers, beekeepers and Department of Agriculture scientists.
"We're getting closer and closer to the point where we don't have enough bees in this country to meet pollination demands," said entomologist Dennis vanEngelstorp of the University of Maryland, who led the survey documenting the declines.
Beekeepers lost 31 percent of their colonies in late 2012 and early 2013, roughly double what's considered acceptable attrition through natural causes. The losses are in keeping with rates documented since 2006, when beekeeper concerns prompted the first nationwide survey of honeybee health. Hopes raised by drops in rates of loss to 22 percent in 2011-2012 were wiped out by the new numbers.
The honeybee shortage nearly came to a head in March in California, when there were barely enough bees to pollinate the almond crop.
Had the weather not been ideal, the almonds would have gone unpollinated -- a taste, as it were, of a future in which honeybee problems are not solved.
"If we want to grow fruits and nuts and berries, this is important," said vanEngelstorp. "One in every three bites [of food consumed in the US] is directly or indirectly pollinated by bees."
Scientists have raced to explain the losses, which fall into different categories. Some result from what's called colony collapse disorder, a malady first reported in 2006 in which honeybees abandon their hives and vanish. Colony collapse disorder, or CCD, subsequently became a public shorthand for describing bee calamities.
Most losses reported in the latest survey, however, don't actually fit the CCD profile. And though CCD is largely undocumented in western Europe, honeybee losses there have also been dramatic. In fact, CCD seems to be declining, even as total losses mount. The honeybees are simply dying.
"Even if CCD went away, we'd still have tremendous losses," said entomologist Diana Cox-Foster at Pennsylvania State University. "CCD losses are like the straw that breaks the camel's back. The system has many other issues."
Studying these issues isn't easy. In real-world agricultural settings, it's hard to run the rigorous, every-last-variable-controlled experiments on which definitive conclusions are founded. These experiments can be run in labs and small-scale test fields, but whether those accurately reflect real-world complexity is debated.
Amidst the uncertainties, scientific attention has settled on a group of culprits, the most high-profile of which is a class of pesticides known as neonicotinoids. These were developed in the 1990s, rushed to market with minimal studies of potential harms, and subsequently became the world's most-used pesticides.
In the last several years, it's become evident that neonicotinoids are extremely toxic to honeybees and, even in small, sub-lethal doses, make bees more vulnerable to disease. The European Union recently limited neonicotinoid use, and the US Environmental Protection Agency is reviewing their use.
Pesticide companies have fought the restrictions, arguing that neonicotinoids are unfairly blamed. Most non-industry scientists say the question isn't whether neonicotinoids are a problem, but where they fit into a constellation of problems.
"Different studies indicate that this class of pesticide is rather harmful to the bees," said honeybee pathologist Cédric Alaux of the French National Institute for Agricultural Research, who said the EU's restrictions are sensible. "However, we should not be too naive and think that it will solve the bee problem."
Just as important as neonicotinoids, and perhaps more so, are Varroa destructor mites. First detected in the United States in 1987, the mites weaken bees by sucking their hemolyph, the insect analogue of blood, and also transmit viruses and other parasites. A recent USDA report called Varroa "the single most detrimental pest of honey bees."
