A controversial new study of honeybee deaths has deepened a bitter dispute over whether the developed world’s most popular pesticides are causing an ecological catastrophe.
Researchers led by biologist Chensheng Lu of Harvard University report a direct link between hive health and dietary exposure to imidacloprid, a so-called neonicotinoid pesticide linked to colony collapse disorder, the mysterious and massive die-off of bees across North America and Europe.
The study isn’t without critics, who say doses used in the study may be unrealistically high. But the level of a realistic dose is also a matter of controversy, and even critics say the findings are troubling.
“Our result replicates colony collapse disorder as a result of pesticide exposures,” said Lu, who specializes in environmental exposures to pesticides. “We need to look at our agriculture policy and see if what we’re doing now is sustainable.”
Developed in the 1990s as a relatively less-toxic alternative to pesticides that seriously harmed human health, neonicotinoids soon became the world’s fastest-growing pesticide class and an integral part of industrial agricultural strategy. In the United States alone, neonicotinoid-treated corn now covers a total area slightly smaller than the state of Montana.
Like earlier pesticides, neonicotinoids disrupt insects’ central nervous systems. But unlike earlier pesticides, which affected insects during and immediately after spraying, neonicotinoids spread through the vascular tissues of plants. They’re toxic through entire growing seasons, including flowering times when bees consume their pollen.
The first reports of colony collapse disorder came in the mid-2000s from commercial beekeepers, who depending on region have experienced colony losses ranging from 30 to 90 percent. Commercial pollination costs have since skyrocketed, and as wild bees are also afflicted, even naturally occurring pollination is threatened.
Measuring bee declines, however, proved much easier than explaining them. Among a lineup of potential culprits including fungus, mites, viruses, bacteria and pesticides, studies failed to find an obvious, smoking-gun cause — but, piece by piece, evidence against neonicotinoids has steadily accumulated.