Colony collapse disorder (CCD)—the sudden and massive die-off of honeybees—has emerged as one of the most mysterious ecological disasters of the past several years, and one of the most expensive. Around the middle of the last decade, commercial beekeepers began to report that colonies of bees were collapsing without warning, with death rates approaching 30 to 90% of a hive. Even stranger was the behavior of bees in an afflicted colony—worker drones would simply fly away, abandoning their hives and queen to simply die alone in the open. Beekeepers have struggled to adjust, and costs of commerical pollination for crops have soared. About 130 crops in the U.S.—worth some $15 billion a year—depend on honeybee pollination, and if bee populations really did collapse, it would mean an agricultural catastrophe.
That’s why scientists have been working overtime to figure out just what might be causing CCD. Everything from fungi to mites to viruses to bacteria to disruptive new beekeeping techniques have been put against the wall as suspects, with no clear smoking gun. But new research by a Harvard biologist named Chensheng Lu might change that. In a new study to be published in the Bulletin of Insectology, Lu points the finger at the pesticide imidacloprid, a chemical often used on corn plants. Honeybees are now fed with supplements of high-fructose corn syrup—and if Lu is right, we could be killing the bees ourselves. “We’ve actually isolated a single risk factor for CCD,” says Lu. “We really need to be looking at this data.”
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Imidacloprid is a neonicotinoid pesticide, one developed and deployed in the 1990s to replace more toxic chemicals. Neonicotinoids disrupt insects’ central nervous systems—including bees. Of course, commercial hives aren’t exposed to such pesticides directly, but neonicotinoids are unusual in that they can spread through the entire vascular system of plants. The high-fructose corn syrup produced from corn plants that have been dosed with imidacloprid can contain trace amounts of the pesticide.
Since beekeepers harvest the honey produced in a commercial hive, they need to feed their colony something else. Cheap corn syrup has filled that market, and since corn crops began to be dusted with imidacloprid in 2005—around the same time that CCD began to emerge—Lu theorized that bees might be exposed to minute doses of the pesticide through the corn syrup, in addition to the pollen of corn plants. “The other risks factors that have been connected to CCD have been present for years,” says Lu. But the introduction of imidacloprid overlapped with CCD—and that was enough reason for Lu to investigate.
In the spring of 2010, Lu and his colleagues set up four groups of commercial bee colonies, each with five hives. During the summer months they were fed supplements containing zero imidacloprid, a small dose of 20 parts per billion or a very large dose of 400 parts per billion. During the winter months—the period when CCD usually occurs—bees abandoned 15 of the 16 imidacloprid-receiving hives. That was enough to convince Lu. “Nearly all the control hives survived,” says Lu. “This is a study that replicates what’s happening in the natural environment.”
The chemical company Bayer, which manufactures imidacloprid, released a statement denouncing Lu’s study:
- The imidacloprid concentrations selected for testing were NOT based on measured residues in high fructose corn syrup (HFCS), but on a series of implausible and unsubstantiated assumptions.
- The study bees were fed HFCS spiked with different levels of imidacloprid that were far above real-world exposure levels.
- In separate research, analysis from actual field grown corn samples, have shown no detectable imidacloprid residues in HFCS.
- The study lacked replication of test colonies within apiaries and the total number of colonies per treatment group were too few to allow a meaningful statistical analysis of colony survival.
- The authors ignored the scientific consensus that bee health is impaired by multiple factors, including inadequate diet, pests and parasites such as the varroa mite, microbial diseases, mismanaged colonies, and loss of genetic diversity.
But as Brandon Keim notes in Wired, many agricultural scientists believe that bees may indeed be exposed to meaningful levels of imidacloprid—and the chemical could be connected to CCD:
But Jeffery Pettis, a bee biologist at the United States Department of Agriculture, called the results “tantalizing but not conclusive.” With only four colonies used per dose level, the study’s statistical significance is limited, “but I would love to see this study replicated such that the trends … they observed could be actually validated,” wrote Pettis in an email.
Among Bayer’s criticisms is that imidacloprid, a first-generation neonicotinoid, is little-used in the United States. It’s largely been replaced by newer formulations — but these, said pesticide expert Charles Benbrook of The Organic Center, an organic food research consultancy, are chemically similar to imidacloprid.
Even Lu says that he doubts imidacloprid is the only cause of CCD, but he does believe that policymakers need to look more closely at the effects the pesticide could be having on honeybees. And given how important the insect pollinators are to agriculture, that’s good advice to follow.