A new study published in the journal Nature has found that honeybees (Apis mellifera) and buff-tailed bumblebees (Bombus terrestris) could not taste imidacloprid, thiamethoxam, and clothianidin – the three most commonly used neonicotinoid pesticides – and so did not avoid them. In fact, the bees showed a preference for food which contained pesticides: when they were given a choice between sugar solution, and sugar solution containing neonicotinoids, they chose the neonicotinoid-laced food. Another study, also from the journal Nature, has investigated how one of these neonicotinoid pesticides, clothianidin, affects both honeybees and wild bees under field conditions in agricultural landscapes.
The honey bee (Apis sp.). Image credit: Zarapp.
Honeybees, bumblebees and other pollinating insects are important for increasing crop yields. When pollinating crops, they can be exposed to pesticides in floral nectar and pollen.
Several controversial studies have shown that neonicotinoids have negative effects on bee foraging and colony fitness. As a result, public concern has grown over the impact of neonicotinoids on bees and other pollinators.
“Bees can’t taste neonicotinoids in their food and therefore do not avoid these pesticides. This is putting them at risk of poisoning when they eat contaminated nectar,” said Prof Geraldine Wright of Newcastle University, UK, the senior author on the first study.
“Even worse, we now have evidence that bees prefer to eat pesticide-contaminated food.”
“Neonicotinoids target the same mechanisms in the bee brain that are affected by nicotine in the human brain. The fact that bees show a preference for food containing neonicotinoids is concerning as it suggests that like nicotine, neonicotinoids may act like a drug to make foods containing these substances more rewarding.”
“If foraging bees prefer to collect nectar containing neonicotinoids, this could have a knock-on negative impact on whole colonies and on bee populations.”
The findings imply that even if alternative food sources are provided for bees in agricultural landscapes where neonicotinoid pesticides are used, the bees may prefer to forage on the neonicotinoid-contaminated crops.
“Since neonicotinoids can also end up in wild plants growing adjacent to crops, they could be much more prevalent in bees’ diets than previously thought,” added co-author Prof Jane Stout of Trinity College Dublin.
The second study shows that honeybees can cope with exposure to the pesticide clothianidin, but that it has a strong negative impact on wild bees.
“We saw a clear negative impact on growth and ability to reproduce in bumblebee colonies near treated rapeseed fields,” said Dr Maj Rundlöf of Lund University, Sweden, who is the lead author on the study.
“As well as problems with growth and reproduction, there were also fewer wild bees on the treated rapeseed fields.”
However, the team found no negative effect on colony growth of honeybees.
“The results show that it is inappropriate to use clothianidin on rapeseed. We need alternative preparations and new cultivation methods if we are to continue growing spring rapeseed in Sweden,” said co-author Dr Thorsten Rahbek Pedersen of the Swedish Board of Agriculture.
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Sébastien C. Kessler et al. Bees prefer foods containing neonicotinoid pesticides. Nature, published online April 22, 2015; doi: 10.1038/nature14414
Maj Rundlöf et al. Seed coating with a neonicotinoid insecticide negatively affects wild bees. Nature, published online April 22, 2015; doi: 10.1038/nature14420
