The largest pollination event in the United States takes place in the almond fields of California, where farmers truck in 85 percent of the hives in America every year. But for the past decade, beekeepers have complained about failing colonies, in which underdeveloped bees were ejected from hives.

According to a podcast from Christopher Intagliata at Scientific American, a pesticide additive called organosilicone surfactants may be to blame. A study out of Penn State came to this conclusion after feeding organosilicone surfactants to bees and then exposing them to common beehive viruses.

“They found that larvae exposed to the chemical and the viruses together appeared to die in greater numbers than did bees exposed to the viruses or the chemical alone, so there’s a possible synergistic effect at play,” says Intagliata.

Hundreds of thousands of pounds of organosilicone surfactants are used in almond orchards each year.

“It’s all over the place,” says Penn State entymologist Julia Fein. “If we can find that it has any effect in an organism it will be relevant.”