There have been marked increases in overwintering
mortality of managed honeybee populations in recent decades
(para. 8) [Data]. It has been suggested that insecticides
(particularly neonicotinoids) may be wholly or partly
responsible. The weak evidence base cannot at present
resolve this question although honeybee declines began
before the wide use of neonicotinoids and there is poor
geographical correlation between neonicotinoid use and
honeybee decline [Exp_op]. Two studies using different
structured methodologies have explored this question.
There has been concern that were pollinators to
use guttation fluid as a source of water they would
ingest highly toxic levels of insecticides. The available
evidence does not suggest that pollinators collect guttation
fluid containing neonicotinoids to any great extent,
in part because it chiefly is present at times of the year
when crops are unattractive to pollinators and other
sources of water are present [Exp_op].
http://rspb.royalsocietypublishing.org/content/281/1786/20140558.full.pdf
