Neonicotinoids are the most widely used insecticides in the world, though their detrimental effect on honey bee populations has stirred controversy in the U.S. and sparked lawsuits from two of Ontario’s largest honey producers. Now, researchers have revealed another startling byproduct of this popular insecticide: Toxic slugs.


Neonicotinoids are commonly sprayed on soybean seeds to keep insects from eating them, but slugs are mollusks, which is a different phylum of creature. It turns out that, while neonics can certainly kill insects, the same poison is simply absorbed by the gray garden slug (Deroceras reticulatum). In fact, the poison remains within the slug and can kill the predatory ground beetles that eat them.

In a study published Thursday in the Journal of Applied Ecology, researchers detail how they allowed slugs to eat soya bean seeds treated with the neonicotinoid thiamethoxam coating. They then released the slugs along with predaceous beetles (Chlaenius tricolor) to see how the toxin interfaced between the two species.

By the end of the experiment, about 60 percent of the beetles had been impaired or killed by the toxin-saturated slugs. Meanwhile, the lack of predatory beetles caused the soybean density to drop 19 percent, lowering crop yields by five percent.

“Seed applications of neonicotinoids are often viewed as cheap insurance against pest problems, but our results suggest that they can sometimes worsen pest problems and should be used with care,” says Penn State’s Margaret Douglas, the lead author on the study.

“In our research with the slugs, it’s quite clear that these [neonicotinoid] seed treatments aren’t doing [growers] any favors,” co-author and entomologist John Tooker told Motherboard.

To eliminate the problem of toxic slugs, Tooker suggested eliminating pesticides and allowing diversity in the crop foodweb to naturally take care of itself.

Though neonics effects on humans are still under debate, the U.S. government is sufficiently worried about their effects on bees to bar the use of the insecticide on federal land. Starting in January 2016, neonicotinoid pesticides will be banned from all federal wildlife refuges, about 150 million acres nationwide.

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