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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.