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Over the last year, beekeepers in the U.S. lost nearly half their honeybee hives. And there are a lot of suspected culprits for this so-called beepocalypse—from parasitic¹ mites², to viruses, to simple land use changes. But a study out earlier this year pointed³ to another possibility: poor sperm⁴ quality among the drone bees, leading to colony crashes. And now another group of researchers may have found a reason for the subpar sperm: neonicotinoid pesticides⁵. These substances contain chemicals similar to nicotine⁶ and affect insect nervous systems. 

"So for the drones that were exposed to pesticides during development, it appears there were more dead sperm in their reproductive tracts⁷." Geoff Williams, an entomologist at the University of Bern in Switzerland and Agroscope, a Swiss federal research facility.

Williams and his colleagues studied the effects of two neonicotinoid pesticides on honeybee drones, genetically⁸ assigned to mate with queens. "They've got really big eyes so they can identify these queens flying through the air. They eat and have sex. Or try to have sex at least." 

But in 20 honeybee hives Williams and his collaborators found that those drones exposed to standard environmental levels of the pesticides were shorter-lived, thus having fewer opportunities to mate. And even if the drones did survive, they had nearly 40 percent fewer living sperm than did control bees—meaning the pesticides were acting⁹ like honeybee contraceptives. The study appears in the Proceedings¹⁰ of the Royal Society B. [Lars Straub et al., Neonicotinoid insecticides serve as inadvertent insect contraceptives]

Williams says pesticides are just one of many factors assaulting bees. But it looks like the way farmers treat some crops could adversely¹¹ affect the pollinators those crops also rely on. 

—Christopher Intagliata