Neonicotinoid insecticides can pose a severe threat to grassland plant bug communities

Although pesticides have been proposed as one of the main causes of insect decline, there are still few studies assessing their effects on non-target species under field conditions. Here we investigated the effects of the neonicotinoid insecticide Mospilan®SG (active ingredient acetamiprid) on plant bugs (Heteroptera: Miridae), a dominant group of European grassland insect communities. In a controlled field study, the abundance of three focal species was reduced by up to 92% two days after field exposure at concentrations expected at field margins, with mortality varying among species. Follow-up feeding assays with insecticide-treated host plants in the greenhouse and controlled dose-response laboratory assays confirmed the strong negative effects on non-target species. Strikingly, when comparing the lethal dose 50 derived from Mospilan®SG with a value reported for honeybees using another acetamiprid formulation, the insecticide was over 11,000 times more toxic to plant bugs than to honeybees. In addition, males were 20 times more sensitive than females in the two tested species. Thus, continuous exposure to this neonicotinoid may reduce plant bug populations and promote insecticide-tolerant species, altering community composition. We suggest that sex-specific sensitivity be considered in risk assessment and conclude that the true risk to non-target insects is currently greatly underestimated. Neonicotinoid insecticides can reduce nontarget plant bug abundance at field margins by up to 92%, as shown by a controlled field study; greenhouse and lab tests reveal high susceptibility to neonicotinoids, with species and sex-specific differences.