Pesticides Harm Hive Behavior

Exposure to two common pesticides can interfere with the growth and viability of both honeybee and bumblebee hives, researchers have found. The exposure, they say, may therefore contribute to the devastating loss of bee populations known as colony collapse disorder (CCD). Because of bees’ role as crop pollinators, losses could cause a crisis for agriculture.

Since the CCD phenomenon was recognized in the mid-2000s, scientists have investigated possible causes, including fungal infections, viruses, and pesticides. But no study has been definitive. However, two new reports, one from entomologist Mickaël Henry at the French National Institute for Agricultural Research in Avignon and coworkers, and the other from biological sciences professor Dave Goulson at the University of Stirling, in Scotland, and colleagues, reinforce the pesticide theory.

The reports show that when exposed to pesticides known as neonicotinoids, honeybees have problems returning home after foraging, whereas bumblebee colonies grow poorly and produce fewer queens (Science, DOI:10.1126/science.1215025 and DOI: 10.1126/science.1215039).

The Henry group used radio-frequency ID tags on individual bees to confirm known effects of pesticides on their foraging abilities. They tagged more than 600 free-range bees and then exposed some of them to sublethal doses of the neonicotinoid pesticide thiamethoxam. The exposed bees were twice as likely to die while foraging, implying that the bees’ homing abilities were impaired.

Even more damning for pesticides, says University of Maryland entomologist Dennis vanEngelsdorp, is the Goulson research, in which colonies of bumblebees were exposed to sublethal doses of the neonicotinoid imidacloprid. Six weeks after exposure, colonies were 8 to 12% smaller, and the number of queens produced dropped 85% compared with control hives.

The Goulson work “is likely a game changer,” vanEngelsdorp says. “This reemphasizes a need to develop a different standard by which we evaluate the safety of this class of pesticides,” he says.