LOS ANGELES - Scientists have identified a new suspect in the mysterious die-off of bees in recent years - pesticides that appear to be lethal in indirect ways.
The chemicals, known as neonicotinoids, are designed to target a variety of sucking and chewing insects, including aphids and beetles.
Bees are known to ingest the poison when they eat the pollen and nectar of treated plants, though in doses so tiny that it was not seen as a threat.
But two reports published online Thursday by the journal Science indicate that the pesticides are not so benign.
One study found that bumblebee colonies exposed to amounts of the insecticide similar to what they'd encounter in the wild gained less total weight than colonies that weren't exposed.
Another study used miniature radio frequency chips to track honeybees and found that the pesticide impaired their ability to navigate back to the hive after a feeding expedition.
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"If it's blundering around and can't return to the hive … the bee might as well be dead," said Christian Krupke, an entomologist at Purdue University in West Lafayette, Ind., who was not involved in either study.
Beekeepers became alarmed that honeybees were vanishing from their nests across the U.S. in the fall of 2006 - victims of a perplexing and pervasive malady now known as colony collapse disorder that wiped out as many as 90 percent of bees, in some cases.
Scientists don't know exactly why the ailment strikes, but they believe it results from a combination of habitat degradation, infection by pathogens and parasites and pesticide use. Researchers have also documented sharp declines in bumblebees, which are important crop pollinators but are not domesticated.
The fate of bees is important because they pollinate so many plants, said David Goulson, a biologist at the University of Stirling in Scotland, who led the study involving bumblebees. Losing too many of the world's bees could endanger wildflowers, which in turn would affect birds and butterflies, he said.
Bees also help pollinate scores of fruit and vegetable crops, a service that's estimated to be worth $15 billion to the agricultural industry.
In California alone, growers rely on honeybees to pollinate 90 crops, including avocado, almond, cherry and plum trees as well as vegetables grown from seeds. In the absence of plentiful bees, California growers could be forced to spend about $250 million renting bees to fertilize their crops.
Neonicotinoid pesticides were developed to eradicate insects without threatening mammals. The chemicals, which are incorporated into the tissues, leaves and flowers of plants, target the central nervous system, leading to paralysis and death. Farmers began using them in the early 1990s.
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