Science News reports: A pair of recent papers indicted neonicotinoids, a widely used class of insecticides, for contributing to a catastrophic decline of honeybees, especially since 2006. Hives across North America have been hammered, many by a particularly mysterious syndrome known as colony collapse disorder, or CCD. Now an additional field trial strengthens even more the case arguing that these pollinators have been poisoned by these chemicals.

This latest research also points to a potentially novel source of the chemicals: corn syrup.

CCD tends to occur in winter or early spring, often when bees begin their first foraging trips of the year. In affected colonies, bees leave but fail to come home, despite their hives having adequate food. One suspicion, which is supported by studies released March 29, is that pesticides or some other poison might impair a forager’s memory or behavior.

But Chensheng Lu, an environmental scientist at the Harvard School of Public Health in Boston, was puzzled as to when and where the critical exposures occured. After all, affected bees were disappearing after months without exposure to toxic agents outside the hive. Lu now argues that bees can undergo a chronic poisoning if their hives’ honey was tainted by insecticides that the pollinators encountered months earlier.

During winter, he charges, what looks just like colony collapse disorder largely emptied 15 of his team’s 16 test hives in central Massachusetts. Each had been exposed experimentally for 13 weeks during the summer to low doses of imidacloprid. Growers rely on this and related neonicotinoid insecticides to protect their crops.