More clues have been found in the case of the disappearing honey bees.
Powdery waste blown off from seed planters was found to contain up to 700,000 times the bee's lethal dosage of neonicotinoid insecticides in a Purdue University study. The study also found the insecticides clothianidin and thiamethoxam in dead bees laying in and around hives in Indiana.
"We know that these insecticides are highly toxic to bees; we found them in each sample of dead and dying bees," said Christian Krupke, associate professor of entomology at Purdue and a co-author of the study published in PloS One, in a press release.
The waste dust is mostly harmless talc, which is used to help coat corn, soy and cotton seeds with insecticides. Without the talc, the polymers used to bind the chemicals to the seeds clog up the seed coating machine and in the planters.
But the excess talc brings some of the pesticide with it when it gets blown off into the air when mechanical planters put the seed in the ground. The talc, along with the pesticides, then settles on nearby vegetation.
"Given the rates of corn planting and talc usage, we are blowing large amounts of contaminated talc into the environment. The dust is quite light and appears to be quite mobile," Krupke said.
"Whatever was on the seed was being exhausted into the environment," Krupke said. "This material is so concentrated that even small amounts landing on flowering plants around a field can kill foragers or be transported to the hive in contaminated pollen. This might be why we found these insecticides in pollen that the bees had collected and brought back to their hives."
The research also consistently found the pesticides at low levels in soil, even up to two years after treated seed was planted. Corn pollen also showed traces of the chemicals.
Greg Hunt, a study co-author, noted that the contaminated talc isn't the only threat to the bees. Parasites, pesticides, and other factors are pummeling the pollinators.
"It's like death by a thousand cuts for these bees," Hunt said.