November 18, 2015

expert reaction to new study on neonicotinoid toxicity to honeybees

A paper published in the journal Proceedings of the Royal Society B has examined the effect of neonicotinoid pesticides on honeybees and report that they are harmful to individual honeybees, but that the population as a whole can respond and recover.

All our previous output on pesticides and bees and neonicotinoids is available.

Dr Peter Campbell, Senior Environmental Risk Assessor, Syngenta, said:

“This is a very interesting landscape field study by Henry investigating effects of thiamethoxam treated oil seed rape on honeybee foraging activity and colony performance.

“In order to investigate the effect of exposure the authors calculate an exposure gradient for thiamethoxam in nectar. This is best demonstrated within the Supplementary Information in Figure S2 A. However, what this Figure shows is that measured residues of Thiamethoxam are in fact very low (0.1 – 0.8 ppb). The authors do not give any details regarding the analytical methods used for thiamethoxam in nectar. For example what was the limit of detection and limit of quantification of the methods used?  This is required to better understand the reliability of the residues measured, particularly when they are as low as measured in this study.

“The core figures presented in the main paper (i.e. Figures 2 and 3) are interesting as they show an effect of time on the parameters being reported. However, it would have been more useful to see how  either of these parameters  i.e. excess mortality (Figure 2) or mean proportion of undetected individuals (Figure 3), related to the exposure gradient that the authors have carefully derived.  This would help more clearly test and demonstrate if there was a dose response relationship.  From looking at Figures 3 a & b, it would appear there was no effect of dose as there is no difference between the ‘high exposure’ and ‘low exposure’ bees in these graphs.

“In summary, whilst effects are reported on individually measured forager parameters, the associated reported residues of thiamethoxam were very low (probably close to limits of detection) and there was no demonstration of a dose response effect across the modelled exposure gradient.

“Due to the confounding effect of finding imidicloprid residues, this study presents further questions, i.e. if the reported effects on parameters are real, are they driven by either thiamethoxam or imidicloprid alone or in combination?  What was the source of the imidicloprid in this experiment?  Whilst the authors speculate as to the source of the imidicloprid contamination no investigation was carried out or data presented to conclude on this point.

“Reassuringly, however, even with these unanswered questions, there were still no effects reported at the colony level in this study. This consistent with a number of other published field studies i.e. Pilling et al 2013, Cutler et al 2014, Rundlof et al 2015, which all report no effects of neonicotinoid seed treated oil seed rape on honeybee colonies under field conditions.”

Dr Alan Dewar, Director, Dewar Crop Protection Ltd said:

“I have read the soon-to-be-released paper and found it to be a highly technical, rigorous investigation into the private lives of bees, which was obviously conducted by people who understand how bee colonies work. They have delved into the complexities of the issues with much more care than other recently published studies, and for that reason, my perception is that the conclusions have much more power than some of the brasher headlines.

“The conclusions from this work, which are very simple in contrast to the study itself, show that bees, or at least honey bees, can compensate for adverse effects of pesticides in their environment. It does in fact explain the contradictory results between laboratory and field observations that have been published in the past.”

Dr Christopher Connolly, Reader in the Medical Research Institute, University of Dundee, said:

“This paper makes an important new contribution to our understanding on the potential impacts of neonicotinoids on bees. The authors provide further evidence on the negative impact of neonicotinoids by demonstrating an increased mortality rate on worker honeybees. It is particularly interesting that mortality increases with time, which is consistent with an increasing preference for neonicotinoid-contaminated food (Kessler 2015) and an increased sensitivity following chronic exposure (Moffat 2015). Therefore, a higher dose and increased vulnerability may quicken the impact of neonicotinoids over time. Given the apparently ubiquitous nature of neonicotinoids in our arable habitat, such an escalation may have been occurring for many years.

“Although honeybee colonies may be able to maintain colony strength by switching their production from male (non-working) bees to female foragers, this may have serious implications to honeybee reproduction. Indeed, many beekeepers in the UK are reporting problems with the mating of new queens.

“In summary, this study identifies three new and important consequences of neonicotinoid exposure to honeybees; increased mortality of female foragers, an increasing vulnerability to the effects of neonicotinoids and a consequential reduction in the number of male bees that are required for mating of new queens and the long-term survival of honeybee colonies. It is important to remember that all other insect pollinators do not possess the enormous buffering capacity of honeybees and are therefore more acutely at risk to the impact of pesticides.”

Dr Scott Hayward, Lecturer in Molecular Ecophysiology, University of Birmingham, said:

“This paper provides an important link between lab and field studies investigating the effects of neonicotinoid pesticides on honey bees. There have been multiple reports outlining the detrimental effects of neonics under lab exposures, but negative impacts from field investigations have been less clear cut. This research identifies a clear relationship between neonic exposure in the field and bee mortality. However, the findings are complicated somewhat by an unintended exposure to two different pesticides. Indeed this issue raises a number of new concerns, including the need to better understand the fate of neonic residues already in the environment. The work re-ignites arguments to ban neonics, and certainly comparable studies are now need on other pollinator species given that honey bees are by no means the contributor to crop pollination.”

‘Reconciling laboratory and field assessments of neonicotinoid toxicity to honeybees’ by Mickaël Henry et al. published in Proceedings of the Royal Society B on Wednesday 18th November 2015. 

Declared interests

Dr Peter Campbell: “My employer, Syngenta, manufactures and sells the neonicotinoid Thiamethoxam.”

Dr Alan Dewar: “My business carries out contract field trials for the ag-chem industry and I was also involved in independent assessments of the first and subsequent neonic seed treatments in the sugar beet crop when employed at Broom’s Barn. These were then the first usage of neonics in the UK.” http://www.dewarcropprotection.com/whoAreWe.html

Dr Christopher Connolly: “I have no conflicts of interest.”

Dr Scott Hayward: “no link with these authors and there are no conflict of interest issues.”