One of every three bites of food we consume depends on pollination by honeybees, but these overlooked contributors to our food system are continuing to die in stubbornly perplexing ways.

Beekeeping groups have held exhaustive conferences. Researchers have organized task forces. The U.S. Department of Agriculture has contributed some of its stretched resources to tracking down the cause of the mysterious deaths, and in a report issued last month, delivered a frustratingly complex answer: Many factors may be responsible, from stress to pesticides.

Now agricultural and chemical heavyweights are getting into the mix. Monsanto Co., which two years ago bought an Israeli bee research company, hosts an industry conference on bee health at its headquarters in Creve Coeur this month. Bayer CropScience is building a 5,500-square-foot “bee health center” in North Carolina, and with fellow chemical giant, Syngenta, has developed a “comprehensive action plan” for bee health.

“The beekeeping industry has always crawled on its hands and knees to USDA and universities, begging for help,” said Jerry Hayes, a bee industry veteran recently hired by Monsanto to run its bee research efforts. “Now we have this very large company involved that knows how important bees are to agriculture.”

And to the bottom line. Bees pollinate up to $20 billion in American agricultural crops, a number that gets the attention of the industry. Monsanto, for one, owns Seminis, the country’s largest fruit and vegetable seed producer — and many of those seeds depend on bees. Beyond that, Monsanto and its rivals have a financial interest in developing a marketable cure that has so far remained elusive.

But as researchers, and now the private sector, puzzle over the issue, some scientists and environmental groups are pointing to a major culprit: The very companies working for solutions, they contend, are a main cause of bee deaths in the first place.

CONFLICTING STUDIES

In 2006, beekeepers started noticing that bees were abandoning their hives, a phenomenon scientists dubbed Colony Collapse Disorder. Since then, the American bee population has dropped by an average of 30 percent every year, sending researchers, beekeepers and farmers into a head-scratching frenzy to figure out the cause.

Specifically and somewhat narrowly, the disorder is being blamed on mites and viruses. More broadly, researchers say, it’s a symptom of an agricultural system that relies too heavily on chemicals and monocultures, including the vast swaths of corn and soybeans in the Midwest.

While bees, historically, have not foraged on these crops for food, the widespread presence of single crops means fewer dining options for the bees — and that could be leading to weakened immune systems.

“We have been systematically eliminating flowers that bees require for nutrition and survival,” explained Marla Spivak, a University of Minnesota entomologist and one of the country’s most prominent bee researchers. “We started using lots of insecticides, necessary because monoculture put out feasts for crop pests. Insecticides are designed to kill insects, which depending on the dose can also kill bees.”

The finger, increasingly, is getting pointed at a particular class of insecticides, called neonicotinoids, that have become widely used over the last decade, largely because they are thought to be less toxic to mammals. These neonicotinoids, manufactured by Bayer and Syngenta, are used as seed coatings on most of the corn and soybeans planted in the U.S. Most corn and soybean crops grown here contain genetically engineered traits developed by Monsanto — although there is no established link between those traits and bee health.

Some recent studies suggest neonicotinoids — by some estimates the most widely used insecticides in the world — are highly toxic to bees.

Published last year, a study by Purdue University found that dead bees that had foraged in and around corn fields contained high levels of neonicotinoid compounds. The study was prompted by massive bee die-offs that happened in the spring, when corn planters were spewing neonicotinoid-containing dust.

“I know, definitively, that there’s a relationship between treated seed and spring die-offs,” said Christian Krupke, the study’s lead author. “It (neonicotinoids) blows out behind the planter and gets in the air, it lands on dandelions. It lands on the bees, even.”

While Krupke says there’s no direct link between neonicotinoids and Colony Collapse Disorder, he said, “anything that’s a stressor to bees is a concern now. We know they’re weaker because of it.”

The industry, however, flatly denies any link between bee health and the neonicotinoids it produces.

“There’s no scientific evidence linking neonics with bee health — period,” said Dave Fischer, director of environmental toxicity and risk assessment at Bayer CropScience.

Bayer, he explained, relies heavily on bees for pollination, particularly in its canola fields in Canada, where it brings in 70,000 hives a year to pollinate fields.

“It would be a poor business model if we were poisoning the bees we depend on,” he noted.

The debate over neonicotinoids is likely to get more heated, particularly in the wake of a two-year European Union ban on the compounds, announced on April 29. The vote on the matter was split — with 15 of the 27 EU members voting for the ban.

“It’s a controversial subject,” said Gene E. Robinson, director of the Bee Research Facility at the University of Illinois. “Not all studies agree with each other. It’s a subject that bears more scrutiny.”

It’s also one that some researchers think is almost unnecessary.

While the industry claims the use of neonicotinoids on seeds boosts yields by 6 to 12 bushels an acre, many question that.

Krupke has done side-by-side field trials to determine whether the seed treatments improve yield. “We have not found any difference in yield or root damage — nothing,” he said. “It doesn’t mean it never works. But it means we certainly don’t need to be putting it on every kernel of corn.”

Environmental groups agree, and have called for an EU-style mindset until links are more solidly studied.

“Any kind of reasonably cautious approach — given the severity of the problem — would dictate that we should act sooner rather than later,” said Doug Gurian-Sherman, of the Union of Concerned Scientists, a Washington-based science advocacy group. “And that would be a moratorium on these insecticides, especially since we know they have such negligible impacts on yield.”

‘BEST PRACTICES’

Neal Bergman remembers a seven-year stretch in the 2000s when crop planes doused cotton fields in the Missouri Bootheel with the insecticide malathion.

“They sprayed 400,000 acres of cotton every week,” he said. “It didn’t matter how the wind was blowing or what time of day it was. They sprayed over people, over animals, over beehives — everything.”

For Bergman, who operates the state’s largest bee operation, it was the dousing of beehives, naturally, that worried him most. He says his bee population plummeted, costing him $1 million and almost putting him out of business.

Since then, he’s been wary — and working hard to keep his bees alive. He uses several medicines and gives his hives protein supplements.

“I don’t think the pollen they get is as good anymore,” Bergman said. “And that’s where they get their protein.”

Bergman, echoing many beekeepers, says more coordination is required among farmers so they don’t spray chemicals when the bees are foraging a particular crop. The labels on the chemicals say that farmers shouldn’t apply them when bees are present — but some don’t pay attention, and enforcement is lax.

Human behavior, he says, can have a major impact.

Indeed, more hobbyist beekeepers in urban and suburban areas have started keeping bees in the hope that they can contribute to a solution.

Robert Sears, president of the Eastern Missouri Beekeepers Association, says he thinks that there’s a greater awareness of the problem, and that beekeepers are learning to maintain healthy hives with a multi-pronged approach, using medicines and good hive management techniques.

“I think the best practices are moving in the direction of using soft chemicals and organic treatments,” he said. “There are also mechanical ways to manipulate hives that don’t involve chemicals.”

But time, many worry, is getting short.

“These are little creatures, working behind the scenes,” Robinson said. “You don’t know about them until they’re gone.”