Residue analysis was conducted to determine whether bees were exposed to the
insecticides used on treated corn seeds. Samples of affected bees, from many incident
locations, were analyzed for pesticide residues by the PMRA Laboratory Services or
Ministère de l’Agriculture, Pêcheries et Alimentation Québec. Clothianidin was detected in
approximately 70% of the samples analyzed in Ontario and clothianidin and
thiamethoxam were detected in the samples analyzed from Quebec. On a bee yard basis,
these residues were detected in approximately 80% of the bee yards where dead bee
samples were collected and analysed. Samples of unaffected bees were also analysed and
clothianidin was only detected in one sample at very low levels. Corn seed in Ontario and
Quebec is treated in approximately equal quantities with either clothianidin or
thiamethoxam. Since thiamethoxam is converted to clothianidin, the detection of
clothiainidin in dead bees could indicate exposure to either clothianidin or thiamethoxam.
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