Mitarbeitende

Exposure to pesticides is considered a major threat to bees and several neonicotinoid insecticides were recentlybanned in cropland within the European Union in light of evidence of their potential detrimental effects. None-theless, bees remain exposed to many pesticides whose effects are poorly understood. Recent evidence suggeststhat one of the most prominent replacements of the banned neonicotinoids–the insecticide sulfoxaflor - harmsbees and that fungicides may have been overlooked as a driver of bee declines. Realistic-exposure studies are,however, lacking. Here, we assess the impact of the insecticide Closer (active ingredient: sulfoxaflor) and thewidely used fungicide Amistar (a.i.: azoxystrobin) on honeybees in a semi-field study (10flight cages containinga honeybee colony, for each of three treatments: Closer, Amistar, control). The products were applied accordingto label instructionseither before (Closer)orduring(Amistar) the bloom of purple tansy.Wefound no significanteffects of Closer or Amistar on honeybee colony development or foraging activity. Our study suggests that thesepesticides pose no notable risk to honeybees when applied in isolation, following stringent label instructions. Thefindings on Closer indicate that a safety-period of 5–6 days between application and bloom, which is only pre-scribed in a few EU member states, may prevent its impacts on honeybees. However, to conclude whether Closerand Amistar can safely be applied, further realistic-exposure studies should examine their effects in combinationwith other chemical or biological stressors on various pollinator species.