November 18, 2015

expert reaction to new study on bumblebees and neonicotinoids

Publishing in the journal Nature, a group of scientists has described their research into neonicotinoid pesticides and bumblebees, reporting that bumblebees exposed to such pesticides visited apple trees less frequently and collected pollen less often.

Prof. Felix Wäckers, Lancaster Environment Centre, Lancaster University and Director of R&D in the Biobest Group, said:

“The paper by Stanley et al. set out to investigate the impact of the neonicotinoid thiamethoxam on pollination service delivery. This was tested by exposing fully developed bumblebee colonies to field realistic concentrations of the commonly used insecticide during two weeks, before introducing them to flowering apple trees.

“The neonicotinoid exposure reduced overall flower visits and pollen collection, in spite of the fact that the average duration of individual foraging trips was prolonged. This indicates a reduced pollination efficacy on a colony basis. Fruit set and seed production data confirmed that pollination was negatively affected in thiamethoxam exposed bees.

“While these results may not be surprising in the light of the previously reported evidence on neonicotinoid impacts on pollinator development and behavior, the study is important in demonstrating for the first time that field realistic levels of neonicotinoid exposure actually compromises crop pollination. This shows that also farmers themselves bear an economic cost when using this group of crop protection products.

“The impact on pollination success of wild plant species can be expected to be even more severe as many of these plants are fully self-incompatible and thus are even more dependent on pollination services.

“The impact of neonicotinoids on pollination as shown in the current study may actually have been an underestimation, as the colonies exposed in this study were already further developed as compared to wild bumblebee colonies at the time of apple blossom. The impact of thiamethoxam exposure can be expected to be more pronounced on these small colonies. Also, in fruit production areas, where various varieties bloom at different times, pollinators can be expected to be exposed to neonicotinoids during more than the two weeks tested here.”

Dr Peter Campbell, Senior Environmental Risk Assessor at Syngenta (which manufactures and sells the neonicotinoid Thiamethoxam), said:

“This very interesting study investigated a wide range of pollination related services provided to apple trees in experimental tunnels by bumble bees pre-exposed to thiamethoxam.

“But how relevant is the exposure regime used in this study to real life exposure of bumble bees to thiamethoxam under field use conditions? The dosing used in this study involved  thiamethoxam spiked syrup being placed directly into brood nest for an average of 13 days before colonies were placed into the tunnels, with feeding solutions being refilled  every 1- 3 days, and with colonies only permitted to forage for 1 hour a day. This is not a field realistic method of exposure.

“There was no replication with only one replicate per treatment group, with eight colonies in each. With such low replication it is not clear whether the results could be reproduced.

“Data provided in supplementary information indicate that for experiments where bumble bees were not exposed to thiamethoxam, 29-56% of apple trees did not bear any fruit at all. This indicates that bumble bees alone do not provide a sufficient pollination services to the apple trees in this experiment, and again show how artificial this experiment is compared to real world situation, where a number of different pollinating insects will be providing such a service but were excluded from this study.

“The authors in the main paper focus all their attention on a number of statistically significant potentially adverse effects e.g. reduced bee visitation rate, reduced number of bees carrying pollen, increased length of foraging time and increased number of aborted fruits, to conclude that thiamethoxam has an adverse effects on pollination services. However, they do not highlight the confounding data from their own experiment, best illustrated in Extended Data Table 1, from the supplementary information, which are not consistent or supportive of this hypotheses i.e. no difference in start number of fruit, no difference in fruit set, no difference in end number of fruit and no difference in proportion of trees producing apples. Arguably these latter endpoints where no effect of thiamethoxam was reported, are an equal or better reflection of the ultimate outcome of the pollination service being investigated. Therefore, at best, the data from this experiment are confounding.

“Therefore, the conclusion reached in this study that thiamethoxam impairs pollination services provided by bumble bees to apple trees, is not conclusive, it is premature and only representative of a single experiment conducted under artificial conditions for the apple trees being pollinated and using unrealistically exposed bumble bees.”

Prof. David Goulson, Professor of Biology at the University of Sussex, said:

“This is an interesting new study which demonstrates that bumblebee colonies exposed to neonicotinoid pesticides deliver less pollination than unexposed colonies. The obvious conclusion is that farmers using these chemicals could potentially experience reduced yields, as could their neighbours who may not be using the chemicals. There may also be knock-on effects for pollination of wildflowers growing on or near farms.

“Exposed colonies collected less pollen, something that has been found in several previous studies of the impacts of neonicotinoids on bumblebees. This may be because of reduced fecundity of the queen, reducing demand for pollen to feed to the brood.”

‘Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees’ by Dara A. Stanley et al. published in Nature on Wednesday 18th November. 

Declared interests

Prof. Wackers: “Within my position at Biobest, I am responsible for research on the production and use of commercial bumblebee colonies used to supplement crop pollination. As a leading company in this field, we are concerned about the health and performance of our bumble bees.  However, I do not think this quantifies as a conflict of interest.”

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