The Environmental Protection Agency found a class of pesticides widely used in agriculture and home gardens throughout Washington state and elsewhere caused significant risk to honeybees when applied to some crops, but had little effect when used on others.

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The Environmental Protection Agency (EPA) found a class of pesticides widely used in agriculture and home gardens throughout Washington state and elsewhere caused significant risk to honeybees when applied to some crops, but had little effect when used on others.

It’s the agency’s first scientific risk assessment of the much-debated class of pesticides called neonicotinoids and how they affect bees on a chronic long-term basis. The assessment neither clears the way for an outright ban nor is a blanket go-ahead for continued use of the pesticide. Both the pesticide maker and anti-pesticide advocates were unhappy with the agency’s report.

Honeybees are crucial to our food supply: About one-third of the human diet comes from insect-pollinated plants, and the honeybee is responsible for 80 percent of that pollination. They’re also in trouble, and bee die-offs are a well-documented problem.

“Honeybees are, by far, the most important pollinator we have,” said Tim Lawrence, an assistant professor and honeybee expert at Washington State University. “If you want fruits and vegetables, bees are absolutely essential.”

According to a report for the Washington state Legislature, about 500,000 colonies of honeybees were needed in 2012 to pollinate Washington crops. Commercial beekeepers often move thousands of beehives up the coast to pollinate almonds in California, berries in Oregon and tree fruits in Washington as seasons change, said Erik Johansen, a policy assistant at the Washington State Department of Agriculture (WSDA) who has studied the impact of pesticides on bees. They face myriad threats.

“The honeybee, specifically, has issues with viruses, mites, with nutrition,” Johansen said. “Pesticides can impact bee health. If they’re used incorrectly, they can have negative impact on bees.”

Some advocacy groups target neonicotinoids — the chemical works on insects’ central nervous systems and often are called “neonics” — and call for bans on the chemicals. Recent scientific studies have pointed to problems and pesticide makers dispute those studies and this one from the EPA.

EPA analysis of detailed tests found a clear level of concentration of the pesticide imidacloprid, the most common neonicotinoid, in which things start to go awry. If nectar brought back to the hive from worker bees had more than 25 parts per billion of the chemical, “there’s a significant effect,” namely fewer bees, less honey and “a less robust hive,” said Jim Jones, EPA’s assistant administrator for chemical safety and pollution prevention.

But if the nectar chemical level was below 25 parts per billion, it was as if there were no imidacloprid at all, with no ill effects, Jones said. It was a clear line of harm or no harm, he said.

Levels depended on the crop, Jones said. While nectar of cotton and citrus fruits were above the harmful concentrations, the levels were not harmful for corn — the nation’s top crop by far — most vegetables, berries and tobacco. Other crops weren’t conclusive and need more testing, including legumes, melons, tree nuts and herbs.

The study looked just at commercial honeybees because they are a good surrogate for all pollinators, Jones said. But Lori Ann Burd, environmental-health director of the advocacy group Center for Biological Diversity, criticized the agency for ignoring wild bees, like bumblebees, which studies show are much more sensitive to the pesticides, calling the report “weak.”

Seattle and other Northwest cities actually banned their use on city-owned property.

Lawrence said those efforts make people feel good, but won’t have a substantial effect on the problem.

As important as bees are, insecticides are necessary, too, Lawrence added.

“If we’re going to have good, cheap food, unfortunately, insecticides are going to be part of the equation,” he said. “Pesticides are a problem. They are toxic to bees. But, if they’re used properly, we can live with it.”

That’s where EPA’s risk assessment could be helpful, Johansen said. The study could help WSDA refine how to properly use neonicotinoids. To minimize impact on bees, farmers may need to adjust when pesticides are applied or how much is used on certain crops, he said.

He said it’s possible the pesticide isn’t suitable for certain crops.

Lawrence said he thought the effect would be limited in Washington. His research suggests 95 percent of bees in Washington are exposed to neonicotinoid levels below those that EPA identified as problematic.

Beekeeper Eric Olson, who runs one of the largest operations in the country out of Yakima, said he’d had pesticide problems in the past, but not with neonicotinoids.

“The huge crisis we face is caused by the varroa mite,” Olson said, referring to a common parasite blamed for bee-colony problems. He said mites took out 45 percent of his hives last winter.

Olson said activists pushing for EPA regulation of neonicotinoids are misguided. “If you ban what the farmers have to use right now, you’re either going to go back to that stuff (other pesticides he believes killed bees in the past) or something new that may not be properly vetted,” he said.