AgroPages-French bee study finds "missing link"-Agricultural news

French researchers have found that neonicotinoid pesticides harm individual honeybees, but whole colonies are able to recover in the wild.

This accounts for discrepancies between lab and field studies, they report in 'Reconciling laboratory and field assessments of neonicotinoid toxicity to honeybees' published in Royal Society Journal Proceedings B.

A Europe-wide ban on neonicotinoid use on flowering crops is due to be reviewed at the end of the year. It was introduced two years ago.

Lead researcher Dr Mickael Henry of the French National Institute for Agricultural Research, INRA, said: "European governments have banned the use of three common neonicotinoid pesticides due to insufficiently identified risks to bees.

"This policy decision is controversial given the absence of clear consistency between toxicity assessments of those substances in the laboratory and in the field. Although laboratory trials report deleterious effects in honeybees at trace levels, field surveys reveal no decrease in the performance of honeybee colonies in the vicinity of treated fields. Here we provide the missing link, showing that individual honeybees near thiamethoxam-treated fields do indeed disappear at a faster rate, but the impact of this is buffered by the colonies' demographic regulation response.

"Although we could ascertain the exposure pathway of thiamethoxam residues from treated flowers to honeybee dietary nectar, we uncovered an unexpected pervasive co-occurrence of similar concentrations of imidacloprid, another neonicotinoid normally restricted to non-entomophilous crops in the study country. Thus, its origin and transfer pathways through the succession of annual crops need be elucidated to conveniently appraise the risks of combined neonicotinoid exposures.

"This study reconciles the conflicting laboratory and field toxicity assessments of neonicotinoids on honeybees and further highlights the difficulty in actually detecting non-intentional effects on the field through conventional risk assessment methods."