Comparative assays revealed distinct toxicity characterizations between pymetrozine and flonicamid

Flonicamid is an insecticide with a unique mode of action, primarily inhibiting the feeding behavior of sap-sucking insects. However, its molecular target remains controversial. Reports indicate that both flonicamid and pymetrozine affect insect behavior and mobility. To investigate further, we compared the susceptibility of three insect species (Myzus persicae, Nilaparvata lugens, and Drosophila melanogaster) to flonicamid and pymetrozine under two different feeding postures. Results showed that feeding posture did not affect the survival curves or mean lifespans of the three insects. However, insect lifespans were significantly reduced under exposure to either insecticide compared to untreated controls. The effects of the two insecticides on susceptibility and lifespan under different feeding postures were markedly different: feeding posture significantly influenced the sensitivity of aphids, planthoppers, and fruit flies to pymetrozine but had minimal effects on the sensitivity of aphids and planthoppers to flonicamid. Flonicamid had only a minor impact on fruit flies' sensitivity. Survival curve analysis also revealed significant differences under pymetrozine stress, while no such differences were observed under flonicamid stress. These findings indicate that flonicamid exerts different toxicological effects on target insects (aphids and planthoppers) versus non-target insects (fruit flies), depending on feeding posture. This suggests that the toxicological mechanisms of flonicamid differ substantially between target and non-target organisms, with implications that findings in non-target insects may not directly apply to target pests. Our study provides valuable insights and directions for further research into flonicamid's mode of action, aiding in elucidating its underlying mechanisms.