Monitoring the effects of thiamethoxam applied as a seed treatment to winter oilseed rape on the development of bumblebee (Bombus terrestris) colonies

Researchers compared bumble bee colonies located in oilseed rape fields planted with thiamethoxam coated seed to bumble bee colonies located in oilseed rape fields grown with untreated seed. The researchers reported that there were no detectable adverse effects on the bumble bee colonies located in oilseed rape fields planted with seed coated with thiamethoxam.

While the results of this study are not to be dismissed, we question whether the extent of the study is sufficient to fully understand impact to bumble bee colonies.  Notably, in Figure 2 and Figure 3 of the paper there is a notable increase in activity for both control groups at the end of the season, while this increase in activity is largely absent in the treatment group (transition between week 4 and 5). The treatment groups switch from being the most active colonies in week 4 to the least active colonies in week 5. Since the end of the season is essential for producing viable reproductive members, we question if this may have produced a discernable outcome in colony growth had the experiments continued. This difference was not noted in the text.

It is also notable that this study does not consider the effects of exposure to bumble bee colonies during the essential colony foundation period. As queens search for, and establish, nest sites they are highly susceptible to environmental perturbations. Dust from the planting of coated seed could potentially be released during the time when colonies are being established (see Krupke et al. 2012, Tapparo et al. 2012 ). There is little question that exposure to neonicotinoids during this foundation period, and continued exposure after the crop bloom period, could have profound effects on colony development and is in need of further exploration. The potential effects from exposure to dust from planting is not discussed or considered in the text.