In 2006, when beekeepers began to report that their hives were suffering from a mysterious affliction, a wide variety of theories were offered to explain what was going on. The bees were suffering from a virus, or a fungus, or a mite, or from stress, or, according to one much publicized hypothesis, they were being addled by cell-phone signals. (Supposedly the transmissions interfered with the bees’ navigational abilities.)

The Pennsylvania beekeeper Dave Hackenberg was one of the first to draw attention to the problem of Colony Collapse Disorder, or C.C.D., and, as a result, he became a celebrity, at least in apian circles. I interviewed Hackenberg in the spring of 2007, and he told me he didn’t believe that the culprit was a virus or a fungus or stress. Instead, he blamed a new class of pesticides called neonicotinoids. Now it looks like Hackenberg was onto something.

Over the last few weeks, several new studies have come out linking neonicotinoids to bee decline. As it happens, the studies are appearing just as “Silent Spring,” Rachel Carson’s seminal study of the effect of pesticides on wildlife, is about to turn fifty: the work was first published as a three-part series in The New Yorker, in June, 1962. It’s hard to avoid the sense that we have all been here before, and that lessons were incompletely learned the first time around.

In the first of the new studies, published online in the journal Science, British scientists raised bumblebees on a diet of pollen, some of which had been treated with a widely used neonicotinoid called imidacloprid. Those colonies that had received the treated pollen suffered significantly reduced growth rates and produced dramatically fewer new queens. In the second, also published in Science, French researchers equipped honeybees with tiny radio-frequency tags. They fed some of the bees sucrose treated with thiamethoxan, another commonly used neonicotinoid. Then they let the bees loose to go foraging. The bees that had been exposed to thiamethoxan were much less likely to return to their hives. “We were quite surprised by the magnitude of the effect,” said one of the study’s authors, Mickaël Henry, of the French National Institute for Agricultural Research in Avignon.

In a third study, to be published soon in the Bulletin of Insectology, seemingly healthy honey colonies were fed high-fructose corn syrup that had been treated with imidacloprid. Within six months, fifteen out of the sixteen hives that had been given the treated syrup were dead. In commercial beekeeping operations, bees are routinely fed corn syrup, and corn is routinely treated with neonicotinoids.

“I believe one reason that commercial beekeepers are experiencing the most severe Colony Collapse Disorder is because of the link between high-fructose corn syrup and neonicotinoids,” said the lead author of the study, Chensheng Lu, a professor at Harvard. (Bayer CropScience, one of the world’s largest producers of neonicotinoids, has disputed Lu’s paper, as well as the other two.)

After the results of Lu’s study were reported, I reached Hackenberg on his cell phone. He was in Pennsylvania, where his bees were pollinating apple trees, and he was preparing to take them up to Maine to pollinate blueberries. He told me that because of the freakishly warm weather in the Northeast last month everything was flowering two to three weeks earlier than normal.

“This more or less proves what we thought all along,” Hackenberg said of the three recent studies. He pointed me to a lawsuit that several beekeeping organizations filed in March against the Environmental Protection Agency. It charges that the E.P.A. violated its own rules by allowing clothianidin—yet another neonicotinoid—to be widely used despite the fact that the field studies the agency had ordered on the effects of the pesticide had never been performed. In a leaked memo from 2010, two E.P.A. staff members raised concerns about allowing mustard and cotton seed to be treated with clothianidin, noting that the field tests that had been completed had been deemed to be inadequate.

“I think we’ve got a toxic mess,” Hackenberg told me. “I know we do.”

Neonicotinoids, which were introduced in the nineteen-nineties, are neurotoxins that, as the name suggests, chemically resemble nicotine. They’re what are known as systemic pesticides: seeds are treated with the chemicals, which then are taken up by the vascular systems of the growing plants. According to the Pesticide Action Network, at least a hundred and forty million acres were planted with neonicotinoid-treated seeds in 2010. This is an area larger than California and Florida combined.

In “Silent Spring,” Rachel Carson wrote of systemic pesticides with particularly vivid horror:

The world of systemic insecticides is a weird world, surpassing the imaginings of the brothers Grimm. It is a world where the enchanted forest of the fairy tales has become a poisonous forest. It is a world where a flea bites a dog and dies…where a bee may carry poisonous nectar back to its hive and presently produce poisonous honey.

“The hives were dead silent,” Lu, the author or the corn-syrup study, said of the boxes treated with imidacloprid. “I kind of ask myself: Is this the repeat of Silent Spring? What else do we need to prove that it’s the pesticides causing Colony Collapse Disorder?”

Photograph by Ralph Orlowski/Getty Images.