Gluconeogenic compensation renders glycogen phosphorylase non-essential as an insecticidal target in Plutella xylostella.

Glycogen phosphorylase (GP) catalyzes the rate-limiting step of glycogenolysis and supplies precursors for chitin biosynthesis in insects. Acyl urea compounds structurally related to benzoylphenylurea (BPU) insecticides are potent inhibitors of mammalian GP, raising the question of whether insect GP could serve as an independent insecticidal target. Here, we show that a mammalian GP inhibitor (GPI) potently inhibits recombinant Plutella xylostella GP (PxGP; IC50=2.96 nM), while the BPU insecticide diflubenzuron does not. Molecular docking and MM/GBSA analysis predict that this selectivity reflects differential side-chain engagement. Despite potent in vitro inhibition, GPI exhibits no insecticidal activity, and RNAi-mediated knockdown of PxGP does not impair development or survival. We provide evidence that insects compensate through upregulation of gluconeogenic enzymes (PEPCK, G-6-Pase) and protein catabolism, with enzyme activity measurements confirming ~29% reduction in GP-a activity following RNAi. Fitness assessment reveals transient larval weight loss with complete recovery of pupal weight, adult morphology, and fecundity. These findings demonstrate that GP is functionally non-essential under the tested conditions, likely through gluconeogenic compensation and alternative carbon sources, and highlight the importance of metabolic network redundancy in target-based insecticide design.