Insecticidal activity and mode-of-action of the novel insecticide isofluorpyramide against Plutella xylostella

The diamondback moth (Plutella xylostella) is a globally distributed pest that has developed widespread resistance to multiple classes of insecticides, posing a persistent challenge to cruciferous crop production. Isofluorpyramide is a newly developed isoxazoline insecticide that was created by modifying the structure of fluxametamide. This study aimed to evaluate its insecticidal activity against P. xylostella and to explore its underlying mode-of-action (MoA).

Leaf-dip bioassays revealed that isofluorpyramide exhibited comparable toxicity to fluxametamide against 2^nd-instar P. xylostella larvae, with a numerically lower lethal concentration 50% (0.036 mg L^-1) but overlapping 95% confidence intervals (CIs), indicating no significant difference. It retained similar potency against both susceptible and I4790K (ryanodine receptor mutant) strains. In glasshouse pot experiments, isofluorpyramide significantly reduced leaf damage (P < 0.05) and provided improved protection over fluxametamide. Field trials confirmed its superior and more persistent control over 14 days. Electrophysiology showed isofluorpyramide inhibited Rdl1 subunit-mediated γ-aminobutyric acid (GABA)-induced currents with a numerically lower half-maximal inhibitory concentrations than fluxametamide (overlapping 95% CI, not significant). Molecular docking suggested that enhanced binding affinity stemmed from strengthened van der Waals interactions within the pocket.

Isofluorpyramide is a promising novel insecticide with similar MoA to those of Insecticide Resistance Action Committee Group 30 isoxazoline insecticides (targeting insect GABA-gated chloride channels), and high insecticidal potency. It shows substantial potential for the sustainable management of P. xylostella and may serve as a crucial tool for managing insecticide resistance in agricultural pest populations. © 2026 Society of Chemical Industry.