Fast Company: The world honey bee population has plunged in recent years, worrying beekeepers and farmers who know how critical bee pollination is for many crops. A number of theories have popped up as to why the North American honey bee population has declined–electromagnetic radiation, malnutrition, and climate change have all been pinpointed. A EPA document reveals warnings from EPA scientists about the widespread use of a bee-toxic pesticide.
...Clothianidin, a pesticide produced by Bayer that mainly is used to pre-treat corn seeds. The pesticide scooped up $262 million in sales in 2009 by farmers, who also use the substance on canola, soy, sugar beets, sunflowers, and wheat, according to Grist.
The EPA document (PDF) was put out in response to Bayer's request to approve use of the pesticide on cotton and mustard. The document invalidates a prior Bayer study that justified the registration of clothianidin on the basis of its safety to honeybees:
Clothianidin's major risk concern is to nontarget insects (that is, honey bees). Clothianidin is a neonicotinoid insecticide that is both persistent and systemic. Acute toxicity studies to honey bees show that clothianidin is highly toxic on both a contact and an oral basis. Although EFED does not conduct RQ based risk assessments on non-target insects, information from standard tests and field studies, as well as incident reports involving other neonicotinoids insecticides (e.g., imidacloprid) suggest the potential for long-term toxic risk to honey bees and other beneficial insects.
The EPA's Environmental Fate and Effects Division (EFAD) first expressed concern when the pesticide was introduced, in 2003, about the "possibility of toxic exposure to nontarget pollinators [e.g., honeybees] through the translocation of clothianidin residues that result from seed treatment."
The entire 101-page memo is worth a read.