ChEBI's entity of the month: Neonicotinoid insectides

The latest ChEBI 'entity of the month' highlights the possible link between the use of neonicotinoid insecticides and the rapid decline in the bee population, known as colony collapse disorder.

Two separate reports have shown that exposure to sub-lethal amounts of neonicotinoids resulted in much lower production of queens [1] as well as interference with the bees' ability to navigate and communicate [2], which are vital for the survival of colonies. As a result, in 2013 the European Union (EU) introduced a temporary ban on the use of the three neonicotinoids, clothianidin (CLO), imidacloprid (IMD) and thiamethoxam (TMX), on flowering crops while further scientific and technical evidence was gathered.

The EU's restrictions have been disputed by agrichemical companies and national governments, which have questioned the validity of the studies. Now, two new studies provide a further twist in the saga of neonicotinoid pesticides and their disputed effects on bee health.

Can bees detect neonicotinoid-treated plants?

A key argument of those who originally opposed the ban was that bees in their natural environment would simply choose not to feed on the nectar from neonicotinoid-treated plants. To test this assumption, a research team led by Professor Geraldine Wright at Newcastle University, UK, used neuron recording techniques which showed that neither honeybees (Apis mellifera) nor bumblebees (Bombus terrestris) were able to identify neonicotinoids by their bitter taste and were not repelled by them. The bees were then offered a choice of sugar solutions, with some contaminated by neonicotinoids at levels similar to those found in the nectar of treated crop plants.

Surprisingly, both honeybees and bumblebees showed a preference for some of the pesticide-tainted solutions [3]. The effect was more pronounced with bumblebees and was observed with IMO and TMX, but not CLO. This work shows that bees cannot control their exposure to neonicotinoids in food and implies that treating flowering crops with IMD and TMX presents a significant danger to foraging bees.

A separate field study carried out by a research team led by Maj Rundlöf at Lund University in Sweden focussed on how neonicotinoids influence wild bees in real-life agricultural environments [4]. They used Elado, a commercial insecticide that contains CLO, in field tests with rapeseed and found at the treated sites there were reductions in wild bee density, solitary bee nesting activity and bumblebee reproduction. While these effects were observed in wild bees, no significant impact was seen in honeybees, the subject of many previous studies.

The findings indicate that the contribution of pesticides to the global decline of wild bees may have been underestimated. Also, the lack of a significant response in honeybee colonies suggests that reported pesticide effects on honeybees cannot always be extrapolated to wild bees. Hence, EU officials will have plenty of reading material to consider before the current ban expires.

Pictured: A bee in the grounds of Langdon Court near Wembury in south-west England. The image is a Creative-Commons licensed photograph, taken from Wikimedia Commons.

References

1. 1. Stokstad, E. (2012). Field research on bees raises concern about low-dose pesticides. Science, 335, 1155.
   2. Whitehorn, P.R., O'Connor, S., Wackers, F.L. and Goulson D. (2012). Neonicotinoid pesticide reduces bumble bee colony growth and queen production. Science, 336, 351–352.
   3. Kessler, S.C., Tiedeken, E.J., Simcock, K.L., Derveau, S., Mitchell, J., Softley, S., Stout, J.C. and Wright, G.A. (2015). Bees prefer foods containing neonicotinoid pesticides. Nature, doi:10.1038/nature14414, published online 22 April 2015.
   4. Rundlöf, M., Andersson, G.K.S., Bommarco, R., Fries, I., Hederström, V., Herbertsson, L., Jonsson, O., Klatt, B.K., Pedersen, T.R., Yourstone, J. and Smith, H.G. (2015). Seed coating with a neonicotinoid insecticide negatively affects wild bees. Nature, doi:10.1038/nature14420, published online 22 April 2015.