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Extension > Yard and Garden News > Use caution when reading new bee and pesticide research

Friday, May 23, 2014

Use caution when reading new bee and pesticide research

Jeffrey Hahn, Extension Entomologist

New research about bees and pesticides from Harvard University was recently published by Lu et al. in the Bulletin of Insectology. This research examined honey bee colonies that were fed high fructose corn syrup (HFCS) contaminated with two common neonicotinoids (imidacloprid or clothianidin) during late summer and then observed in the following spring. Both the control colonies and the insecticide exposed colonies did well going into fall. While both sets of colonies then declined, the control colony numbers rebounded while the insecticide exposed colonies suffered large losses. The authors' conclusions are that insecticides are the leading explanation for colony collapse disorder (CCD).

While this seems like compelling information on the surface, there are a number of concerns and flaws about this research that should cause readers to examine it very cautiously. The biggest concern for many is the concentration of insecticides which was fed to bees at a rate of 135.8 parts per billion (ppb), in a volume of 1.9 liters of sucrose water per colony per week, for 13 consecutive weeks. This is considered an extremely high concentration and does not represent a realistic rate of pesticide exposure to bees.


Jeffrey Hahn, University of Minnesota Extension

Photo 1: There are many factors implicated in the decline of bee health.

Interestingly, Dr Lu's own data in his 2012 research paper, also published in the Journal of Insectology, showed that at field-relevant dosages, neonicotinoids did not appear to harm bees (halfway through his research, he abruptly increased the dosage being fed to bees after it appeared that there was greater numbers of capped brood cells occurring when exposed to lower dosages).

The validity of his 2012 study is further held in question by the assumption that significant levels of residues are present in HFCS as a result of neonicotinoid seed treatment of corn, an assumption that was not tested. Eventually Dr. Lu et al. did look at this issue and in a 2013 published paper that found no neonicotinoid residues in any of the tested samples of HFCS and a maximum of 2.2 ppb of imidacloprid present in pollen. This would seem to contradict the premise used in pursuing any of this research.

Other red flags that have been raised include concern for the small sample size which did not allow for sufficient replication and does not allow for such broad conclusions that considers all geographic regions; the failure to fully explain the actual cause for the loss of one of the control colonies; and failing to thoroughly evaluate other commonly accepted stresses in CCD.

It is widely accepted that there are a variety of factors that influence bee health including parasites, diseases, loss of habitat (lack of flowers=poor nutrition), decreased genetic diversity, stresses due to beekeeper and grower practices, in hive pesticides, as well environmental pesticides. More research is needed to better determine which of these factors poses the most important threats to bee health.

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