Synergistic effects of the insecticide flupyradifurone and the entomopathogenMetarhizium brunneumin ants

Abstract Agricultural pesticides such as commonly used neonicotinoids are major drivers of the global entomofauna declines. Furthermore, synergistic interactions between pesticides and other stressors substantially amplify their environmental effects and could therefore have important implications for policy decisions that aim to improve the health of insects. Due to increasing restrictions for neonicotinoid use in the EU and rising pest resistance, alternatives were introduced, such as flupyradifurone, a novel systemic butenolide insecticide that was initially promoted as safe for non-target insects. However, this is increasingly questioned by the accumulation of evidence for harmful effects on pollinators. Furthermore, studies investing effects in other non-target arthropods are lacking. We therefore investigated how chronic exposure to flupyradifurone affects survival of black garden ants Lasius niger . Furthermore, we studied potential interactive effects of field realistic flupyradifurone doses with exposure to the entomopathogenic fungus Metarhizium brunneum . We found that concentrations exceeding 50 ppm result in increased worker mortality, and that field realistic contamination did not reduce food intake. At low concentrations, flupyradifurone exposure alone did not affect survival, but chronic flupyradifurone exposure at sublethal doses increased pathogen susceptibility in ants, indicating a synergistic effect of the two stressors. This first report of synergistic effects between flupyradifurone and pathogens raises further concerns about the long-term impacts of novel pesticides on the health of beneficial insects.