USDA Research Links Neonicotinoid Pesticides to Bee Deaths

(Beyond Pesticides, January 25, 2011)

Research by the U.S. Department of Agriculture’s (USDA) Bee Research Laboratory and Penn State University shows that the neonicotinoid insecticide imidacloprid contribute, at extremely low levels‚ to bee deaths and possibly colony collapse disorder (CCD), the widespread disappearance of honey bees that has killed off more than a third of commercial honey bees in the U.S. While the study has not been published yet, the UK’s The Independent newspaper reports that honeybees exposed to imidacloprid are more susceptible to the fungal pathogen Nosema.

This is the first study to show that neonicotinoids impact the survival of bees at levels below the level of detection, meaning that field studies would not have considered the role of the pesticide, because they would not have detected it. USDA researcher Jeffrey Pettis, PhD and Penn State University researcher Dennis Van Engelsdorp, PhD explained their research in the 2010 documentary, The Strange Disappearance of the Honeybees (transcript courtesy of

[Pettis] I’ve done a recent study actually in collaboration with Dennis van Engelsdorp and some other researchers, where we exposed whole colonies to very low levels of neo-nicotinoids in this case, and then challenged’ bees from those colonies, with Nosema, a pathogen, a gut pathogen. And we saw an increase, even if we fed the pesticide at very low levels‚ an increase in Nosema levels, in direct response to the low level feeding of neonicotinoids‚ as compared with the ones which were fed normal protein.

[Van Engelsdorp] You measure that effect (Nosema infection) at levels that you could not detect the pesticides, and so that brings up the question: if it’s having an effect at that low dosage, we would not have discovered it in our study because it was below the limit of detection. The only reason we knew the bees HAD exposure (to nicotinoid pesticides) is because we exposed them; otherwise we would never have known they had been exposed (to neonicotinoids).

[Pettis] The take-home message is that interactions may be the key. Bee Health is very complex and that these interactions are often overlooked and are hard to tease apart. So in this case we were manipulating ONE pesticide (Imidacloprid) and one pathogen (Nosema Ceranae) and we clearly see the interaction.

Dr. Pettis told The Independent his research had now been put forward for publication. “[It] was completed almost two years ago but it has been too long in getting out,” he said. “I have submitted my manuscript to a new journal but cannot give a publication date or share more of this with you at this time.”

Since the publication of The Independent story and leak of the Environmental Protection Agency (EPA) memo in December showing the agency used flawed science to approve another bee-killing neonicotinoid insecticide, clothianidin, lawmakers in the UK have begun calling for a full ban of all neonicotinoids. Member of Parliament Martin Caton, a former agricultural scientist, told The Independent that the evidence was growing that neonicotinoids are a problem, and that the testing required in Britain and European Union was not rigorous enough. “I think they should be suspended on the precautionary principle while we improve it,” Mr. Caton said. The House of Commons is expected to debate the issue this week, although a full ban is unlikely.

Beekeepers and environmentalists called on EPA December 8, to remove a pesticide linked to CCD, citing the leaked EPA memo that discloses a critically flawed scientific support study.

Clothianidin and imidicloprid are members of the neonicotinoid family of systemic pesticides, which are taken up by a plant’s vascular system and expressed through pollen, nectar and gutation droplets from which bees then forage and drink. Neonicotinoids kill sucking and chewing insects by disrupting their nervous systems. Beginning in the late 1990s, these systemic insecticides began to take over the seed treatment market. Clothianidin is Bayer’s successor product to imidacloprid, which recently went off patent. Both are known to be toxic to insect pollinators, and are lead suspects as causal factors in CCD. Together, the two products accounted for over a billion dollars in sales for Bayer Crop Science in 2009. Imidacloprid is the company’s best-selling product and among the most widely used insecticides in the U.S. Starting in about 2004, seed companies in the U.S. began to market seeds treated with a 5-X rate of neonicotinoids (1.25mg/seed, compared with the traditional 0.25 mg/seed).

Colony Collapse Disorder is the name given to the mysterious decline of honeybee populations around the world beginning around 2006. Each winter since, one-third of the U.S. honeybee population has died off or disappeared (more than twice what is normal). While CCD appears to have multiple interacting causes including pathogens, a range of evidence points to sub-lethal pesticide exposures as important contributing factors. Neonicotinoids are a particularly suspect class of insecticides, especially in combination with the dozens of other pesticides found in honeybee hives. Key symptoms of CCD include: 1) inexplicable disappearance of the hive’s worker bees;2) presence of the queen bee and absence of invaders; 3) presence of food stores and a capped brood.