What does the evidence say? Scientists issue statement on the science for neonicotinoids and pollinator deaths

By Nathan Gray

- Last updated on GMT

Neonicotinoids and bee deaths: What does the science say?

Related tags Beekeeping

An international team of scientists have called for an 'evidence-driven debate' on the links between neonicotinoids and pollinator bee deaths, as they publish a 'restatement' of the scientific evidence.

The restatement of the scientific evidence on neonicotinoids aims to clarify the scientific evidence available on neonicotinoids, to enable an 'evidence driven debate' and help stakeholders to develop coherent policies and practice recommendations, said the group.

Led by by Professor Charles Godfray and Professor Angela McLean from the Oxford Martin School at Oxford University, the publication of the restatement in Proceedings of the Royal Society B​ sets out the evidence (what it is, and the quality of it) in a series of short statements and summaries that "we hope will really make it comprehensible to people that don't have a technical background, without compromising on the science."

"What we have tried to do ... as far as possible being policy neutral, is to try assemble evidence relating to neonicotinoids on pollinators, and set it out in a series of statements,"​ Godfray told FoodNavigator.

"For each statement we have an assessment of the evidence, whether it is strong experimental, or expert opinion - whether it is indicative, but we need more evidence,"​ he explained - noting that the 46 evidence summaries can be found online in the appendix of the restatement.

In reaction to the study, Professor Ian Boyd, Chief Scientific Advisor at Defra, said: “It is essential that policies on the use of pesticides are built on sound scientific evidence. This paper provides an independent assessment of this subject, which will provide clarity and authority in order to help people make more informed choices." 

"We are trying our best to be honest brokers in this,"​ said Godfray. "The purpose was not to say that the neonicotinoids ban was either good or bad."​ 

"But, insecticides kill insects - that's what they are meant to do. And so it's no surprise that if pollinators are exposed to neonicotinoids ​[at lethal doses], that they die."

Lethal vs sub-lethal doses

The Oxford expert told us that there is a 'fairly strong consensus' that the exposure of pollinators to neonicotinoids in a field will nearly always not lead to lethal doses - and so all the issues and debate revolve around sub-lethal doses.

"What we try and do is to show what the evidence is for sub-lethal doses, and also where the evidence gaps are,"​ he explained - noting that a major issue with current research is that many studies showing an effect of sub-lethal doses may not be representative of field conditions.

"We show that most of the experiments have used doses at the high end or really beyond what is likely in the field,"​ said Godfray. "The information about field relevant doses is not absent, but is much weaker than the totality of the evidence."

"We have very poor information about it. It's very easy in the lab to show that a sub-lethal dose can affect the behaviour or longevity of an individual, but what's much harder to show is what the effects are for the colony or at the population level."

Evidence restatement

The full restatement, found here​, provides 46 statements that tackle key issues and sets out where the scientific evidence stands on many important points in the debate on neonicotinoids and pollinator deaths.

"The statements are based on the evidence in peer-reviewed scientific literature, though the annotated bibliography also notes the existence of information in non-reviewed reports and industry studies,"​ wrote Godfray and his colleagues.

The key findings are as follows:

  • There are several proven pathways through which pollinators may be exposed to neonicotinoid insecticides, however quantitative information about the extent and significance of these different routes is poor.
  • Lab studies have strengths in that they allow carefully controlled experiments on individual insects at a well-defined exposure. They have weaknesses in that these conditions are often 'artificial'. Nevertheless, lab studies provide important information about the range of concentrations where death or sub-lethal effects may be expected.
  • Field monitoring data has found low levels of residues in surveys of honey bees and honey bee products. Data from the field is 'relatively few' and restricted to a limited number of species.
  • Field experiments have issues regarding whether doses received are representative of what they will receive under normal use of neonicotinoids in the field - as it appears most studies have used concentrations 'at the high end of those expected'.
  • To understand consequences of changing the neonicotinoid use, it is important to look at colony-level and population processes, and the likely effect on a pollination ecosystem. The possibility that crop producers change agronomic practices in response to bans must also be taken in to account.

Source: Proceedings of the Royal Society B
Volume 281, Number 1786, Open Access, doi: 10.1098/rspb.2014.0558
"A restatement of the natural science evidence base concerning neonicotinoid insecticides and insect pollinators"
Authors: H. Charles J. Godfray, Tjeerd Blacquière, et al

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