Role of pesticides in bee decline: scientists call for evidence-driven debate

Wednesday, May 21, 2014 - 09:00

An international panel of scientists is calling for an evidence-driven debate over whether a widely used type of insecticide is to blame for declines in bees and other insect pollinators.

The Oxford Martin School published on May 21st the second in its "restatement" series. Restatements take an area of current policy concern and controversy and attempt to set out the science evidence base in as policy neutral way as possible. They also provide a commentary on the nature of the evidence base.

The restatement, from a group of nine scientists led by Professor Charles Godfray and Professor Angela McLean from the Oxford Martin School, attempts to clarify the scientific evidence available on neonicotinoids to enable different stakeholders to develop coherent policy and practice recommendations. 

The study is published in the Proceedings of the Royal Society.  It is open access and can be downloaded from the Royal Society website here or you can download a single pdf of the paper with the Annotated Bibliography.

An EU ban on certain neonicotinoid insecticides was introduced in December 2013 because of fears they were harming pollinating insects. Pollination by insects is critical for many crops and for wild plants but at the same time neonicotinoids are one of the most effective insecticides used by farmers. Potential tensions amongst the agricultural and environmental consequences of neonicotinoid use have made this topic one of the most controversial involving science and policy.

Professor Charles Godfray said: “Pollinators are clearly exposed to neonicotinoid insecticides, but seldom to lethal doses, and we need a better understanding of the consequences of realistic sub-lethal doses to the insect individual, bee colony and pollinator population.”

Professor Angela McLean added; “A major question to be addressed is what farmers will do now that they face restrictions on the use of neonicotinoids. Will they switch to crops that need less insecticide treatment or might they apply older but more dangerous chemicals?”

The restatement describes how much insecticide is present in a treated plant and how much is consumed by pollinators. It goes on to summarise how neonicotinoids affect individual bees and other pollinators, and the consequences at the colony and population levels.

In reaction to this 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." 

Paul de Zylva, from Friends of the Earth, commented: “This project is an important step toward much needed public and scientific debate and scrutiny. The Government should support and fund both more open science and safer ways to grow crops as part of its National Pollinator Strategy due in July.”

Any corrections and clarifications will be pasted below.

June 2nd 2014.  We were asked to comment on a paper published too late to include in the Restatement.  Were it to have been included it would have followed paragraph 35.

(35A) Lu et al. 2014.  Honeybee colonies (six per treatment) were fed with syrup containing imidacloprid, clothianidin or with no added insecticide for a 13 week period from July to September (in Massachusetts, USA).  It was estimated that each bee consumed 0.74 ng insecticide per day.  The number of frames within each hive colonised by bees were monitored over the subsequent winter.  Five out of six control colonies and either two (imidacloprid) or four (clothianidin) out of six colonies in the neonicotinoid treatments survived.  From mid-winter control hives were reported to have significantly more occupied frames than insecticide treated hives.

(a) The quoted average consumption of neonicotinoid insecticides is 3-12 times higher than the worse-case nectar ingestion rates calculated in Para. 22e; the assumption of a constant 50,000 bees per colony is high and were it lower the consumption rate would be even greater.  Foraging bees, which consume more food, will also experience higher exposure.

(b) We were not able to understand the statistical analysis from the description in the paper and requested sight of the raw data (May 28th), which has not yet been granted. 

Lu, C, Warchol, K.M. & Callahan, R.A.  (2014).  Sub-lethal exposure to neonicotinoids impaired honey bees winterization before proceeding to colony collapse disorder.  Bulletin of Insectology67, 125-130.

June 5th 2014. Error in Reference 13 corrected.


Photo of Honeybee (Apis mellifera) collecting pollen from catkins of goat willow (Salix caprea); photograph courtesy of Bram Cornelissen.

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