Pesticide-Coated Seeds Are More Dangerous To Helpful Insects Than Was Thought

Neonicotinoid-treated seeds—basically seeds dipped in Roundup—have exploded in popularity since the mid-2000s.

But the precise environmental effects of this kind of seed treatment isn’t particularly well-understood. Evidence is mounting that these treatments can slaughter bee colonies, which has led some, like the state of Minnesota, to call for a ban. Bees, though, aren’t the only unintended target of neonicotinoid-treated seeds.

There has been a long-standing belief among some that the seed-coating treatments do not adversely affect non-targeted insects like the tiger beetle, pictured above. The tiger beetle is a predatory insect, which is a scary name for a bug that farmers should actually love: it feeds on aphids, caterpillars, and slugs, and will even eat the seeds of weeds. Farmers have no reason to want these guys dead, in addition to the fact that killing large numbers of any animal can throw off an entire ecosystem.

A new study from the entomology department at Penn State finds that, in direct contrast to this long-standing belief, neonicotinoid-treated seeds do in fact pose a significant risk to predatory insects like the tiger beetle. The study examined more than 20 different field studies, crunching the numbers in various ways, to find out exactly how these seeds affect predatory insects, and the results are scary: a reduction in predatory insect populations by 10 to 20 percent.

One of the key findings of this study is an indication that the treated seeds and the plants that grow from them are actively toxic to these insects. It has long been assumed that any reduction in predatory insect population comes from a simple reduction in their food sources: pesticides are designed to kill aphids and weeds, major food sources of the predatory insects, and so the predatory insect population would naturally drop.

But the study did not find a similar drop in the population of predatory spiders, which have most of the same food sources as the predatory insects. In other words, there must be some another factor than simply less food to result in such a large decrease in predatory insect numbers—and that factor could well the treated seeds.

It’ll take lots more research before we fully understand the impact that treated seeds have on the environment, but this initial research is a bit scary. The tiger beetle is a farmer’s friend!