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Corn prices remain quite high, driven up by the summer’s prolonged drought. And since the United States is by far the globe’s largest corn producer, prices will likely stay high until the next bumper crop in the Midwest replenishes global corn reserves. To take advantage of high prices, US farmers will likely plant a whole lot of corn in spring 2013-at least as much as they did in 2012, which marked a 75-year high in corn acreage. And that could be bad news for bees, commercial honey-producing ones and wild bumblebees alike, both of which have experienced severe declines in recent years.

What does the health of bees have to do with the corn crop? A growing weight of evidence links a class of pesticides called neonicotinoids, which are used on nearly the entire US corn crop, to declining bee health. In March, I looked at three studies that had just been released, two of them published in the prestigious journal Science, making the link. Those papers came on the heels of a damning one from Purdue University researchers (which I discussed here). And now comes yet another, this one (abstract; I have the full study but can’t upload it because of copyright issues) published by UK researchers in another prestigious publication, the British journal
Nature.

The researchers treated 40 colonies of bumblebees over four weeks as follows: 10 got exposed to tiny doses of a common neonicotinoid pesticide (10 parts per billion, a level within a range of what bees experience in corn fields); 10 got exposed to small doses of another common pesticide, this one of the pyrethroid class; 10 were exposed to both pesticides; and 10 served as the control group, and were kept free of pesticides. The bees were tracked with radio frequency identification (RFID) tagging technology.

The results: Both groups of neonic-treated bees saw sharp declines in overall worker bee productivity. The bees treated with only pyrethroids fared a little worse than the control, but not much. The ones treated with both pesticides fared worst of all-suggesting a possible cocktail effect, meaning that pesticides combinations may work in ways that mutually amplify the effects of the individual pesticides.