Exposure to Clothianidin Seed-Treated Canola Has No Long-Term Impact on Honey Bees
We conducted a long-term investigation to ascertain effects on honey bee, Apis mellifera L., colonies during and after exposure to ßowering canola, Brassica napus variety Hyola 420,grown from clothianidin treated seed. Colonies were placed in the middle of 1-ha clothianidin seed-treated or control canola Þelds for 3 wk during bloom, and thereafter they were moved to a fall apiary. There were four treated and four control Þelds, and four colonies per Þeld, giving 32 colonies total. Bee mortality, worker longevity, and brood development were regularly assessed in each colony for 130 d from initial exposure to canola. Samples of honey, beeswax, pollen, and nectar were regularly collected for 130 d, and the samples were analyzed for clothianidin residues by using high-performance liquid chromatography with tandem mass spectrometry detection. Overall, no differences in bee mortality, worker longevity, or brood development occurred between control and treatment groups throughout the study. Weight gains of and honey yields from colonies in treated Þelds were not signiÞcantly different from those in control Þelds. Although clothianidin residues were detected in honey, nectar, and pollen from colonies in clothianidin-treated Þelds, maximum concentrations detected were 8- to 22-fold below the reported no observable adverse effects concentration. Clothianidin residues were not detected in any beeswax sample. Assessment of overwintered colonies in spring found no differences in those originally exposed to treated or control canola. The results show that honey bee colonies will, in the long-term, be unaffected by exposure to clothianidin seed-treated canola.