Countrywide field study highlights negative effects of neonicotinoids on bees

A new study published in Nature has just found a correlation between the death of honeybee colonies and the use of neonicotinoid pesticides in the UK. The fact that bees’ chronic exposure to neonicotinoid insecticides reduces their survival is well known. It has been proven by several laboratory trials. The originality of this study is that it was carried out in the field and on a countrywide scale.

The publication highlights the impacts of imidacloprid, which is the active substance of pesticides such as Gaucho ® (cereals) or Confidor ® (fruit trees, ornamental plants,…). The study explains that in England and Wales, oilseed rape area rose from 293 378 hectares in 2000 to 602 270 ha in 2010. In the same period, the use of imidacloprid seed treatment increased from 1% in 2000 to 75% in 2010.

Based on the fact that coated seeds only provide partial pest control and that they leads to pest resistance development, the cost-benefit calculation concludes that the promised seed-coating benefits (i.e. foliar spray reduction and yield increase) are small when compared to their costs (i.e. bee colony losses and smaller yields in practice than in theory). In this way, the study clearly refutes the economic argument that leads farmers to use neonicotinoids.

These substances do not only affect pollinating insects. Indeed, groundwater and rivers are also concerned as stressed by a recent US study. In order to understand neonicotinoid fate, water samples were collected in rivers all around the US.

At least one neonicotinoid was detected in 53% of the samples. Imidacloprid was detected the most (37%), followed by clothianidin (24%), thiamethoxam (21%), dinotefuran (13%), acetamiprid (3%). Thiacloprid was not found. Clothianidin and thiamethoxam were rather found in agricultural areas while imidacloprid was mostly found in urban areas.

Such studies challenge neonicotinoids environmental impact and their agronomic and economic interest. Such publications must change the mind of policy makers who still believe that these harmful molecules can be offset by economic interest.

Authors: A. Fayet, C. Cardoso

See also: Report - an interim impact assessment of the neonicotinoid seed treatment ban on oilseed rape production in England