Toxicological effects of a difenoconazole fungicide on a non-target butterfly

Agricultural intensification, driven by increasing food demand, is one of the main drivers of global biodiversity loss. Pesticides, including fungicides, may increase crop yield but pose substantial threats to the environment. However, our current knowledge on the effects of fungicides on biodiversity suffers from less research interest compared to other pesticides and a neglect of insect herbivores. We here investigate the effects of a commercially available, ready-to-use difenoconazole fungicide on a non-target insect, the butterfly Pieris napi, under controlled laboratory conditions. When being fed with fungicide-treated host plants, butterfly larvae showed a strongly reduced survival (15%) compared to controls (60%). Survival in larvae treated with the fungicide plus an insecticide was only 1%. Sublethal effects of the fungicide included prolonged development and reduced adult size. Our results indicate a surprisingly high toxicity of the tested fungicide formulation on P. napi. Based on the available literature, we speculate that triazole fungicides may be in general toxic to Lepidoptera and potentially other herbivorous insects. This study contributes to the growing evidence that fungicides may well be involved in the loss of insect biodiversity in agricultural landscapes at the global scale.