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Environmentalists and beekeepers are calling on the government to ban some of the country's most widely used insect-killing chemicals.
The pesticides, called neonicotinoids, became popular among farmers during the 1990s. They're used to coat the seeds of many agricultural crops, including the biggest crop of all: corn. Neonics, as they're called, protect those crops from insect pests.
But they may also be killing bees.
Christian Krupke, a professor of entomology at Purdue University in Indiana, is among the scientists whose research has alarmed beekeepers. Last month, I caught up with Krupke at a DoubleTree Hotel in Bloomington, Ill., where he was giving a talk to several hundred farmers and the agricultural consultants who advise them about seeds, fertilizer and pesticides. The meeting was organized by GrowMark, a farm supply company.
This was a skeptical audience, filled with people who make their livings using or selling pesticides. They listened quietly as Krupke laid out the reasons why neonicotinoids have fallen under suspicion.
These pesticides are typically applied to seeds — mainly of corn, but also other crops — as a sticky coating before planting. When a seed sprouts and grows, the chemicals spread through the whole plant. So insects, such as aphids, that try to eat the plant also get a dose of poison.
But could they be killing more than aphids? Krupke put up a picture of a beehive surrounded by a carpet of dead honeybees. In several places across the Midwest, there have been reports of bees dying in large numbers like this. And tests detected the presence of neonics on them.
It seemed like a mystery. How could bees come into contact with chemicals that are buried in soil with crop seeds?
Krupke put up another slide: a picture of a huge machine that's used for planting corn. This equipment is apparently part of the answer.
These machines use air pressure to move seeds from storage bin to soil. A slippery powder — talc or graphite — keeps everything flowing smoothly. The air, along with some of the powder, then blows out through a vent.
Krupke explained how he tested that planter exhaust and found amazing levels of neonic pesticides: 700,000 times more than what it takes to kill a honeybee.
That toxic dust lands on nearby flowers, such as dandelions. If bees feed on pollen from those flowers, that dust easily can kill them. A tell-tale clue: These bee die-offs all happened during corn-planting season.
The farmers clapped politely when Krupke's talk was over. There weren't many questions.
Krupke has given this talk to several farm groups. Most farmers just listen, he says, but some are moved to action.
Each time, "it's probably at least two or three people who will say, 'I care enough about this problem that I will seek to not use these materials,' " he says.
Some environmentalists believe that this shouldn't be left up to farmers to decide. They say the Environmental Protection Agency needs to step in.
Last week, a coalition of environmental groups and beekeepers sued the EPA, demanding that the courts force the agency to revoke its earlier approval of two of the most prominent neonicotinoids — clothianidin and thiamethoxam.
Towers says that the problem with these pesticides goes well beyond those cases where lots of bees died all at once — maybe because of toxic dust from corn planters.
Neonics also show up in the pollen of corn, canola and sunflowers that grow from treated seed. Bees feed on that pollen. The amount of pesticide they get is so small that it won't kill the bees outright. But Towers says it may have other effects: "Disorientation; reduced ability to gather food; impaired memory and learning; and lack of ability to communicate with other bees."
Towers says this low-level exposure to neonics, from millions of acres of seed-treated crops, may be weakening honeybee hives, killing them slowly.
Bayer CropScience, the biggest seller of these pesticides, insists that most studies show that neonics are quite safe.
David Fischer, the company's director of ecotoxicology, says that in the real world, one cannot observe these chemicals causing any widespread harm to bees. For instance, he says, "in Canada, virtually all the canola is grown from neonicotinoid-treated seed. And the health of bees in that area of Canada, the prairie provinces, is as good as anywhere else in Canada."
Yet Bayer CropScience is reacting to reports of bee kills. The company is working on a new system for planting corn that replaces the powder in planting machinery with a waxy substitute. The company says just making that change can cut the amount of neonics released from corn planters by 50 percent.
For critics of these pesticides, though, cutting releases in half isn't good enough.
Copyright 2013 NPR.