Neonicotinoid and EBI fungicide in combination hazard the population of red mason bees under field conditions

Mixing several agrochemicals, e.g., insecticides, fungicides, and herbicides, is a common practice by farmers, enhancing the economic and efficacy of a single application. Their effects on non-target organisms are not routinely evaluated during the authorisation of single products. A field study was conducted in Germany to assess the performance and exposure level of red mason bees after application of a combination of products containing the insecticide thiacloprid and the fungicide prochloraz to winter oilseed rape. The number of offspring of exposed bees was significantly reduced by 49.8 % compared to unexposed bees. Lower residues of applied active substances were found in mud walls than in pollen provision. The maximum detected concentrations in pollen provisions were 129.95 µg/kg for thiacloprid and 149.96 µg/kg for prochloraz, whereas 4.70 µg/kg for thiacloprid and 65.83 µg/kg for prochloraz in mud walls. An application restriction during flowering will minimize exposure and mitigate the high risk. • A significant decrease in flight activity of red mason bees in the treated fields compared to control. • Reduction in the number of offspring of exposed red mason bees. • Lower residues of applied active substances in mud walls than in pollen provision. • Exposure to a mixture of thiacloprid-prochloraz is hazardous to red mason bees.