April 28, 2016

expert reaction to the effects of different neonicotinoids on bumblebees

There is growing concern over the impact of the neonicotinoids to insect pollinators and how their loss may limit the ecosystem services that are vital to our food production (globally worth US$215 billion) and the stability of our natural environment. In a new study, published in Scientific Reports, researchers directly relate the effects of three neonicotinoids, at the level of individual brain cells to their impact on whole colonies of bumblebees placed at 5 different sites across Scotland. These comments accompanied a briefing.

Dr Peter Campbell, Senior Environmental Risk Assessment Specialist at Syngenta, which manufactures and sells the neonicotinoid Thiamethoxam, said:

“The paper attempts to link changes at the receptor level following exposure to three neonicotinoid insecticides to short-term acute mortality and on through to the consequences on long-term colony health in bumble bees using continuous exposure to treated syrup. There are a number of inconsistencies, over-interpretation of data, and the use of rather tenuous links (e.g. extrapolating effects of long-term nicotine effects in man to effects of neonicotinoid insecticides on bumble bees) to explain the results found. Inconsistencies include how thiamethoxam, but not clothiandin, has a negative effect at the colony level when clothiandin is a major metabolite of thiamethoxam formed in bumble bees, as shown in this study. The apparent colony effects reported in this study for thiamethoxam also contradict a previous study¹, which reported no adverse effects on bumble bee micro-colonies at similar levels of exposure over an extended period.

“It is important to note that the colony studies were conducted by directly feeding colonies with spiked sucrose, which is not representative of exposure of wild bumble bees under normal field conditions. The colony level results reported from these studies are also inconsistent with other reported colony studies with bumble bees, probably due to the single post-exposure assessment point approach selected. It is well established that the bumble bee colony endpoints monitored in this study are both highly variable over time and between colonies. For example, numbers of queens and drones produced can be highly variable both within colonies over time and between different colonies and years; drones can also exit the colonies as they are the same size as workers. The significant effect reported for thiamethoxam on ratio of males to females, nest size etc. could equally be attributed to the thiamethoxam colonies moving from colony growth mode to reproductive phase earlier than the other colonies. The paper itself highlights differences based on the source of the colonies and even between the untreated colonies on 2 consecutive years.

“To conclude, this study struggles to explain the inconsistent results found across the receptor binding, laboratory and colony experiments, which often contradict each other as well other previous published data. In particular, it used an inadequate single ‘end of experiment measure’ of colony performance in a highly variable system. It also fails to recognize that there is an increasing body of published evidence that report no effect of neonicotinoids on bees under realistic field conditions of use.”

¹ Ian Laycock, Katie C. Cotterell, Thomas A. O’Shea-Wheller, James E. Cresswell  (2014). Effects of the neonicotinoid pesticide thiamethoxam at field-realistic levels on microcolonies of Bombus terrestris worker bumblebees. Ecotoxicology and environmental safety, Vol. 100, 02.2014, p. 153-158.

Prof. Lin Field, Head of Biological Chemistry and Crop Protection at Rothamsted Research, said:

“This paper reports an interesting data set that shows different effects of different neonicotinoids on bumblebees. It is especially interesting to see that at colony level one of the compounds, clothianidin, showed no detrimental effects. It is known that different neonicotinoids show different direct toxicity to bees, as do different members of other chemical classes (pyrethroids and organophosphates) so we should maybe not be surprised at these results.

“The authors are right to conclude that each pesticide/insect combination needs to be considered independently and we shouldn’t extrapolate across a chemical class or across species. The effect of a chemical on an insect will depend on many factors including differences in the chemical’s structure or the target site protein, in addition differential uptake and metabolism will affect toxicity.”

Dr Mike Garratt, an ecologist at the Centre for Agri-Environmental Research at the University of Reading, said:

“This is an important and timely study. As the body of evidence for negative effects of neonicotinoids on non-target species mounts, it is important to consider the differential effects of these chemicals and this new research clearly demonstrates not all are equally harmful.

“This study only considers impacts on one species of bumblebee. Similar variability in toxicity might be expected for other species of bee and non-target organism, and it is important to remember there are more than 200 distinct bee species in the UK alone.

“This work once more highlights the clear evidence gaps regarding the wider effect of this type of insecticide. Much more work needs to be done if these serious policy decisions, with wide-ranging impacts on our food supply and environment, are to be based on the best scientific evidence.”

‘Neonicotinoids target distinct nicotinic acetylcholine receptors and neurons, leading to differential risks to bumblebees’ by Christopher Moffat et al. will be published in Scientific Reports at 2pm UK time on Thursday 28^th April, which is also when the embargo will lift.

Declared interests

Prof. Field: “Some of the work in my department at Rothamsted is supported financially by Agro-Chemical companies, including Bayer and Syngenta, but I personally receive no remuneration from any companies.”

Dr Garratt is an employee of the University of Reading working on research funded by UK research councils, Europe FP7, DEFRA and the UK Insect Pollinators initiative. He is convenor of Royal Entomological Society Pollination Special Interest Group and a member of the British Ecological Society, Royal Entomological Society, Society for Conservation Biology, and has involvement with the WorldBeeProject charity.

Dr Campbell’s employer, Syngenta, manufactures and sells the neonicotinoid Thiamethoxam.