Following a request from the European Commission, EFSA performed a comparison between the doses of several neonicotinoids tested in the studies from Henry et al. (honeybees, thiamethoxam) and Whitehorn et al., (bumblebees, imidacloprid) (Science, 2012) with potential exposure of bees following actual use of neonicotinoids. In these studies, the authors suggested that field-realistic levels of neonicotinoids thiamethoxam and imidacloprid might have a considerable effect on colony stability and survival of honeybees and bumblebees. A third study investigating similar effects on honeybees for clothianidin and imidacloprid was also considered (Schneider et al., 2012).
To compare the actual exposure of bees to residues arising from the EU authorised uses with doses investigated in the published research, EFSA collected data on the products and their uses authorised in the Member States (GAP tables), as well as information on the uses considered representative for the active substance approvals (review reports). The available residue data in pollen and nectar, as provided to the Member States by the applicants, were also collected in order to define the extent of the contamination of these feed items resulting from the authorised uses.
A comparison was made between the EU representative uses, as reported in the review reports of the active substances, the uses authorised in the Member States, and the application rates investigated in the residue studies. Overall, the available residue data in nectar and pollen were limited and available only for seed treatments of maize (only pollen), oilseed rape, Phacelia, alfalfa and sunflower; therefore the extrapolation to crops, other than those mentioned above, was not considered appropriate.
The available highest residue levels of thiamethoxam, clothianidin and imidacloprid in nectar were compared with the actual concentrations tested on honeybees by Henry et al. and Schneider et al. and the results of the comparison indicated that the tested concentrations were higher than the concentrations found in nectar. When the residue intake was estimated using different exposure scenarios, the results indicated that the doses tested by Schneider et al. for imidacloprid were higher than the potential estimated exposure. However, the doses tested for clothianidin by Schneider et al. and for thiamethoxam by Henry et al. were lower than the potential estimated exposure in some scenarios. These results indicate that sub-lethal effects following the use of these active substances could not be fully excluded in worst case situations. However, it should be noted that there are several uncertainties regarding these results, therefore, they should be considered with caution. In particular, in the studies from Henry et al and Schneider et al. bees consumed the total amount of active substance within a relatively short period and not administered over a longer period i.e. a day. Depending on the substance properties and how fast the substance can be metabolised by the bees, this method of exposure could have lead to more severe effects than what may occur when bees are foraging.
The concentrations tested on bumblebees by Whitehorn et al. were in the range of the maximum exposure residues of imidacloprid in pollen and nectar. However, it is uncertain as to what extent the exposure situation in the study is representative to field conditions since bumblebees would need to forage for two weeks exclusively on imidacloprid-treated crops in order to be exposed to the same extent as in the study. Further consideration would be necessary to understand whether this situation may occur in intensive monoculture landscapes.
The results of the published studies were considered unlikely to be of relevance for other neonicotinoids (i.e. acetamiprid and thiacloprid).
Overall, before drawing definite conclusions on the behavioural effects regarding sub-lethal exposure of foragers exposed to actual doses of neonicotinoids it would be necessary to repeat the experiments performed in the studies with other exposure levels or in other situations.