July 9, 2014

expert reaction to new study associating use of a neonicotinoid with decline in population of some birds

Nature published a study reporting a correlation between declines in farmland bird populations in the Netherlands and use of the neonicotinoid pesticide imidacloprid. A before the headlines analysis accompanied these comments.

Dr Dave Moore, Senior Scientist at CABI, said:

“The paper once again demonstrates that effective alternatives to chemical pesticides are urgently needed. If a fraction of the money spent on chemical insecticide research was spent on developing biological pesticides, we could have environmentally safe methods of delivering control that would have many benefits over the chemicals. Not least of the benefits would be increased control of pests by the biodiversity killed as collateral damage by chemicals. Biological pesticides can be incredibly cheap to develop and can deliver control that is as effective, though with different characteristics, as chemicals.”

Dr Raimund Grau, Senior Ecotoxicologist at Bayer CropScience, said:

“The hypothesis of the authors and their conclusions primarily build on data sets which were already published by van Dijk et al. (2013). This referenced publication used the same imidacloprid surface water data set to claim declines in Dutch surface water invertebrates and was recently rebutted in another publication by Vijver and van der Brink (2014).  The published rebuttal criticised both the method used and the conclusions reached in this analysis. In particular, the measurement of imidacloprid residues and macro-invertebrate monitoring were not even taken from the same locations, nor at the same time.  The study of Van Dijk et al. (2013) has also been evaluated by the authorisation board in The Netherlands, Ctgb. Ctgb concluded that this study cannot be used to show a causal relationship between the concentration of imidacloprid and the number of observed species.  Therefore, if this conclusion that imidacloprid causes declines in Dutch surface water invertebrates is not reliable, then drawing the additional conclusion that the same imidacloprid water residues are responsible for bird population declines that feed on these aquatic invertebrates, is even less plausible.

“The basis for the correlation of “concentration in water” leading to “decline in food resource, as the investigated species live on emerging insects” is not substantiated. Most of the birds on the list are not foraging to a large extent on insects emerging from water bodies. Some of the species showing significant negative correlations have a diet that would be dominated by invertebrates other than those with aquatic life stages e.g. skylarks predominantly feed on ground dwelling Coleoptera, spiders etc., Mistle thrush on earthworms, snails etc., Starling on leatherjackets and other soil invertebrates.

“No attempt is made to account for other possible sources of the reported “decline” like change of habitat. Two of the authors (van Turnhout and Foppen)[1] in 2010 concluded “that trophic mismatches (consequent on climate change) may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.” This conclusion was for forests but agricultural areas are even more seasonal. Therefore this known aspect should have been considered in an unprejudiced research project, especially when in this study too all the exclusively insectivorous species with a significantly negative trend are long-distant migrants.

“Overall, this is a correlational study of potential indirect effects of imidacloprid on birds and does not test causality. The strong bias of the publication is evident e.g. by a sentence like this “However, as our results are correlative, we cannot exclude other trophic or direct ways in which imidacloprid may have an effect on the bird population trends. Food resource depletion may not be the only or even the most important cause of decline. Other possible causes of decline include trophic accumulation of this neonicotinoid …”. Other potential causes of a bird population decline are not even mentioned.”

[1]Both,C. et al., Avian population consequences of climate change are most severe for long-distance migrants in seasonal habitats Proc. R. Soc. B. 2010 277 1685 1259-1266doi:10.1098/rspb.2009.1525  

Prof Charles Godfray FRS, Oxford Martin School, Oxford University said:

“The strength of this work is that it brings together for the first time datasets on bird populations and neonicotinoid concentrations in the environment to ask very important questions.  But as the authors acknowledge it is a correlative study and there will be debate about the detailed statistical methodologies used (for example whether all confounding variables have been accounted for and whether spatial covariance in the data has been adequately dealt with).  What I take from this paper and other work on the effects of neonicotinoids on insect pollinators is the enormous importance of setting up large, replicated field experiments in real agricultural landscapes to get much harder data on the effects of this class of insecticide on all elements of biodiversity.”

Declared interests

Prof Godfray is Chair of Defra’s Pollinator Expert Advisory Group

Dr Grau’s, employer, Bayer CropScience, manufactures neonicotinoids including Imidacloprid

‘Declines in insectivorous birds are associated with high neonicotinoid concentrations’ by Caspar Hallmann et al published in Nature on Wednesday 9 July.