New study from Harvard first to link imidacloprid directly to Colony Collapse Disorder

[Press release Harvard School of Public Health] Imidacloprid, one of the most widely used neonicotinoid pesticides, has been named as the likely culprit in the sharp worldwide decline in honey bee colonies since 2006. Researchers at the Harvard School of Public Health say their new research provides "convincing evidence" of the link between imidacloprid and colony collapse disorder. "It apparently doesn't take much of the pesticide to affect the bees," says Alex Lu, associate professor of environmental exposure biology at Harvard's Department of Environmental Health, "Our experiment included pesticide amounts below what is normally present in the environment."

The Harvard team's research results will appear in the June issue of the Bulletin of Insectology.
Lu and his research team hypothesized that the rise in CCD resulted from the presence of imidacloprid, a neonicotinoid introduced in the early 1990s.
Bees can be exposed in two ways - through nectar and pollen from treated plants or through high-fructose corn syrup which beekeepers use to feed their bees. As most U.S.-grown corn (maize) is treated with Imidacloprid when it is planted, imidacloprid is also found in corn syrup derived from those plants.
In the summer of 2010, the researchers conducted an in situ study in Worcester County, Massachussetts, aimed at replicating how imidacloprid may have caused the CCD outbreak.
Over a 23-week period, they monitored bees in four different bee yards; each yard had four hives treated with different levels of imidacloprid and each yard contained one un-treated 'control' hive.
After 12 weeks of imidacloprid dosing, all the bees were alive. But after 23 weeks, 15 out of 16 of the imidacloprid-treated hives - 94% - had died. Those exposed to the highest levels of the pesticide died first.
Lu says the characteristics of the dead hives were consistent with CCD - the hives were empty except for food stores, some pollen, and young bees, with few dead bees nearby.
When other conditions cause hive collapse-such as disease or pests-many dead bees are typically found inside and outside the affected hives.

Strikingly, said Lu, it took only low levels of imidacloprid to cause hive collapse, less than what is typically used in crops or in areas where bees forage.

Download full study: Lu et al, 2012 In situ replication of honey bee colony collapse disorder Bulletin of Insectology 65 (1): 99-106, 2012

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Weaknesses in the Harvard study

We recommend to read the commentary by Randy Oliver ( on "The Harvard Study on imidacloprid and CCD"

Also of interest is the official reaction by Bayer Cropscience:
Bayer CropScience Says Bee Study is “Seriously Flawed”. Bayer fails hovever to mention that a major fraction of corn in US is treated with other neonicotinoids such as clothianidin or thiamethoxam. See for instance the study by Krupke et al. 2012: Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields.