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.
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"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.