In a spring ritual as old as life itself, Steve Ellis' bees return to their hives day after day loaded with pollen from the dandelions and flowering trees that are in full bloom across central Minnesota.

But for too many of them, a day of foraging ends in convulsions and death.

"You wouldn't think people could get attached to insects," said Ellis, a commercial honey producer from Barrett, Minn. "But it's hard for us to see our bees getting injured like that."

Hard enough that Ellis and other beekeepers from across the country last month asked the federal government for a temporary ban on one the most widely used pesticides until its effect on bees is clear. They fear it is contributing to a worldwide die-off and the inexplicable phenomenon known as "colony collapse disorder" that is devastating honeybee hives.

"We are asking the EPA to do its job," said Jeff Anderson, a commercial beekeeper from Eagle Bend, Minn. "Give us products that are safe."

The beekeepers and several environmental groups argue in an emergency petition filed with the EPA that the agency failed to require some legally mandated field testing before the pesticide was approved in 2003. New research, including two studies published last week in the journal Science, raises serious questions about its effect on pollinators of all kinds, they maintain.

The EPA said it has based its continued approval on hundreds of studies. In 2010, the agency said no data show that bee colonies are harmed by exposure. Nevertheless, it agreed to accelerate its routine review of the pesticide – meaning it will be completed in 2018.

Meanwhile, officials with the manufacturer, Bayer CropScience, say they are confident that the research will continue to prove the product is safe for bees when used appropriately.

"I tend to believe that science will win out over emotion," said Jack Boyne, director of communications for Bayer CropScience.

The beekeepers and others say they filed the emergency petition because they fear that the EPA's review process will deliver a verdict too late for the nation's honeybees and the farmers who rely on them.

"Seventy percent of crops – apples, oranges, zucchini, melons, strawberries – they all need pollinators," said Vera Krischik, an associate professor of entomology at the University of Minnesota who studies the pesticides and bees. "It's a huge issue."

Then there are the unknown numbers of bumblebees, wasps, butterflies and other wild pollinating insects that fill the same role across the natural world.

"We are headed in a very dangerous direction," Ellis said.

Anderson said beekeepers have always been on the front lines of the nation's pesticide wars; that's how he got into business in the first place. His wife's grandfather moved his California beekeeping business to Minnesota in the early 1960s after another pesticide, Sevin, critically damaged his agricultural pollinating business.

Anderson went on to win a landmark case at the Minnesota Supreme Court against the state Department of Natural Resources over pesticide drift that killed his bees.

Like Ellis, he is among the gypsy beekeepers who follow the seasons, pollinating almonds, cherries and other crops in the South and West in winter and returning to Minnesota in the spring to make honey.

The pesticides beekeepers are fighting now are different than those of the past, Anderson said. Those were applied at predictable times, making it easy to keep bees out of harm's way.

The pesticides most widely used now are among a class of nicotine-based chemicals called neonicotinoids that are designed to become an intrinsic part of the plant. They were developed in large part because they are much less toxic to humans and other mammals than previous pesticides. But in high doses, they are a neurotoxin to insects.

Since their introduction in the 1990s, they have exploded in popularity among farmers and in products for home gardeners. Today, 90 percent of seed corn is coated with the pesticides before planting, and the chemicals are the active ingredient in hundreds of backyard products.

The pesticide is sprayed on plants and, when used as a seed coating, it grows into all parts of the plant, including the pollen and the nectar that bees eat.

When used properly, say both Bayer and the EPA, the toxin levels are not high enough to hurt bees. But many scientists and beekeepers say that, as in all pesticide regulation, the field research is questionable because it's done by the manufacturer.

The emergency petition, filed by 30 beekeepers and national environmental groups that includes Beyond Pesticides and the Center for Food Safety, targets just one of the six neonicotinoids, clothianidin, in part because they say the field study for that one was inadequate. Officials from Bayer and the EPA disagree.

The attorney for the environmental groups said he hopes the petition will prompt the agency to open up the issue up for public comment and discussion. EPA did not respond to questions about the petition, but it previously announced plans to hold a scientific meeting in the fall to consider the entire class of pesticides, which will include the latest research.

All pesticides in the group work the same way, and none of the research underlying their approval by the EPA has taken into account "the cumulative effect" in bees, Krischik said.

Beekeepers say it helps explain what they are seeing.

"During corn planting we have a light kill on our bees," Anderson said. "And the inability of the colony to produce a good brood."

He thinks that as farmers plant millions of acres of corn, dust from the pesticide-coated seeds floats out over the countryside. It lands on bees and other flowering plants and builds up over time in the soil.

"My theory is that some of the things that come up, like dandelions, are coming up toxic," he said. "Every year they come up more toxic."

Then, in August and September, when bees forage for pollen in corn tassels, the colonies are weakened just when they need to produce the brood that must be strong enough to survive the winter. Anderson said 15 to 20 percent of his bees used to die in a year. Now, the death rate has doubled, and beekeepers all over the country are seeing the same thing, he said.

Meanwhile, honey prices are up significantly, as are the prices he charges to California growers for pollination, Anderson said.

Neither beekeepers nor scientists think that the pesticides are the sole cause of bee declines and the collapse of colonies. Other studies have also implicated viruses, parasites and loss of habitat.

"Bees have a host of diseases and parasites that are killing them, in addition to being exposed to pesticides from all classes," said Marla Spivak, a bee researcher at the university who last year won a MacArthur genius grant for her work.

But the systemic pesticides could make pollinators vulnerable to other dangers, or, as one the studies in Science last week found, confuse them so much they can't find their way home.

But none of that indicates that the pesticides pose an imminent hazard that would justify a ban, said Iain Kelly, director of the Bayer CropScience bee research team.

Still, the EPA needs to do risk assessments that are based on solid research, scientists said.

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That way, said Ellis, the beekeepers and the farmers can figure out how to take care of the pollinators – just like the bees take care of them.

"It's a symbiotic relationship," he said.