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expert reaction to FERA study / Defra analysis of neonicotinoids and bumble bee colony decline

A report by the published by the Food and Environment Research Agency (FERA), and an accompanying analysis by Defra, concluded there was no link between bee health and exposure to neonicotinoid pesticides.

 

Dr Lynn Dicks, Research Associate at the University of Cambridge and NERC Knowledge Exchange Fellow, said:

“The study finds fairly consistent exposure to neonicotinoids in free-living bumblebee colonies.  One or more of the chemicals were found in at least some colonies at all three test sites, including the control site, which was next to a 6.5 ha field of oilseed rape not treated with neonicotinoid.

“The actual neonicotinoids found in pollen and nectar collected by the colonies were not the same as the chemicals used on the treated fields the colonies were next to.  Thiamethoxam was found at the highest levels, although it was not used on the treated fields included in the experiment. Use of thiamethoxam has rapidly increased in the UK in the last three years – 250,000 ha were treated with it in 2010.

“This finding is important because it shows very clearly that this design of field trial, with bumblebee colonies placed at the edge of treated or untreated fields (fields were 6.5 to 12 ha in size) is not sufficient to compare the effects of neonicotinoid exposure against control ‘untreated’ colonies.  I am not at all surprised by this.  It is well known that bumblebees forage over several kilometres.

“Levels in bumblebee-collected nectar and pollen in the field ranged from detectable but too low to measure quantities up to an average of 2.4 μg/Kg (equivalent to parts per billion) of thiamethoxam in nectar for colonies at one site.  Average levels of 0.7 μg/Kg of thiamethoxam were found in pollen at two of the three sites.  This is lower than the 6 ppb used in pollen by the Whitehorn et al experiment, where they measured an 85% drop in queen production (Whitehorn et al. 2012), although Whitehorn used imidacloprid, which was only found below the levels of quantification at one of the sites in this study.  The different neonicotinoids do not necessarily have the same toxic or sublethal effects.

“There are not consistent and strong statistical correlations between the degree of exposure to different neonicotinoids via different routes, and colony mass or queen production, at these levels of exposure.  The study uses two statistical approaches.  Some significant effects are found, but there seem to be no cases for which a strong statistical signal is found using both approaches.  For example, one approach (potentially powerful but with strong assumptions) finds an effect of clothianidin in nectar on colony mass at end of study.  The other approach (cruder but with fewer assumptions) finds effects of all measures of neonicotinoid exposure on colony mass after 3-4 weeks, but not at the end of the study.  On queen production, little overall effect is found by either approach.

“If the effect was strong and clear, a range of different statistical approaches would detect it.  The effect here isn’t massive, or overwhelming like the effect on queen production found by Whitehorn et al.  Even at the site with the least productive colonies, they produced an average of 16 queens/ colony, which is comparable to buff-tailed bumblebee colonies measured in other situations (control colonies in Whitehorn et al.’s study produced 13 queens on average, for example).

“However looking at the data in the report (Figure 7, page 26) it seems there could be some subtle impacts on bumblebee colony performance at these exposure levels. I would like access to the raw data.

“The reporting of statistical results in this study is difficult to interpret.  The main results table (Table 7) does not explain what the different rows mean.  Results are reported as the percentage of models from 1000 partially simulated datasets that found ‘a significant effect’.  Some linear model results are given in the Appendix (p 51 onwards), but they are not well explained.  It is not clear to me how these relate to the results presented in Table 7.  We can’t easily see the strength of interactions between different response variables in these different test runs.  Does the effect of clothianidin in nectar change according to the exposure to thiamethoxam in pollen, for example?  What happens if you don’t include the simulated data for the colonies exposed at levels below the quantifiable threshold?

“The study monitored 60 buff-tailed bumblebee colonies Bombus terrestris, with 20 colonies at each of three sites in Lincolnshire or Yorkshire.  It shows, as expected, that buff-tailed bumblebees are not feeding exclusively on oilseed rape even in intensive arable landscapes in the early summer.  Only 13-26% of the pollen collected by the bumblebees was from oilseed rape.  This may also be true for nectar.

“Overall, the consistency and levels of exposure to neonicotinoids in free-living bumblebee colonies revealed by this study are not surprising, given the use of these chemicals in the landscape.  As a society, the results should make us think carefully about the impact of our agricultural practices on wild bees and other insects.  The bee species used, the buff-tailed bumblebee, is common, widespread and not known to be declining.  The findings should prompt urgent and very careful consideration of the effects of such consistent exposure on other, more vulnerable species.”

 

Prof Francis Ratnieks, Professor of Apiculture at the University of Sussex, said:

“The results of this study are a contribution to our knowledge on the effects of neonicotinoid insecticides on bees.  The bumble bee, Bombus terrestris, colonies studied foraged heavily on oil seed rape (OSR), which provided over 1/3 of the pollen collected.  Most oil seed rape in the UK is treated with neonicotinoid insecticides, and as oil seed rape is a crop that has flowers that produce pollen and nectar it is an obvious and presumably major route by which bees may pick up these chemicals from the environment. 

“The colonies were set up in 3 places, one adjacent to fields of OSR untreated with neonicotinoids, and one each adjacent to fields treated with two different neonicotinoids, clothianidin and imidacloprid.  There was no difference in the proportion of young queens reared by colonies at the three locations. 

“This is interesting in the light of a lab study published in 2012 by researchers from Stirling University that found that imidacloprid reduced the proportion of queens reared by colonies of B. terrestris.  It is a pity that one group of colonies was not set up in an area without oil seed rape, or ideally with only an untreated field.  The field without oil seed rape was 1km from other fields of oil seed rape that may have been treated, and samples of pollen and nectar from colonies at this location did have thiamethoxam (in all 19 nectar samples) and in 9 of the pollen samples.  Clothianidin was also detected, but not imidacloprid. 

“Bumble bees are known to forage at distances of over 1km and it seems likely, therefore, that the colonies had found other oil seed rape fields to forage in.  Overall, the results of this study are inconclusive.  As the authors state: ‘“The absence of these effects [on colony success and on proportion of young queens reared] is reassuring but not definitive’.  More studies on colony performance under field conditions are needed, including studies on honey bees as well as bumble bees.”

 

Defra Chief Scientist Ian Boyd said:

“Decisions on the use of neonicotinoids must be based on sound scientific evidence.  The analysis of laboratory studies published by Defra today demonstrates that while we cannot rule out the possibility of neonicotinoids affecting pollinators we cannot be clear as to the extent of their impact.

“Some of the studies analysed did not replicate the realistic dosage which bees and other pollinators would be exposed in the natural environment.  The results of a study by Fera – also published today – into the foraging habits of bees on crops treated with neonicotinoids seems to support this assessment, as the Fera study suggests bumble bee forage over large distances.

“I therefore support the conclusions of the analysis that further data based on more realistic field trials is required.”  

 

Defra analysis: http://www.defra.gov.uk/environment/quality/chemicals/pesticides/insecticides-bees/

Original FERA study:
http://www.fera.defra.gov.uk/scienceResearch/scienceCapabilities/chemicalsEnvironment/documents/reportPS2371Mar13.pdf

 

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