Exogenous 20-Hydroxyecdysone (20E) rescues chlorantraniliprole-induced developmental impairment in Bombyx mori based on Ca2+ homeostasis.

Chlorantraniliprole (CAP), a widely used diamide insecticide, can exert effects on insect development and metabolic homeostasis through low-concentration environmental residues. However, it remains unclear whether exogenous 20-hydroxyecdysone (20E) can rescue CAP-induced developmental impairment. In this study, we systematically investigated CAP-induced developmental delay and its rescue by exogenous 20E in fifth-instar Bombyx mori larvae. The results showed that CAP exposure (0.01 mg/L) significantly prolonged the duration of the fifth instar and reduced whole-cocoon weight. Supplementation with exogenous 20E (20 mg/L) partially shortened the developmental delay but failed to restore whole-cocoon weight. Transcriptomic analysis revealed that CAP exposure induced only limited transcriptional reprogramming, whereas 20E supplementation under CAP stress broadly activated pathways related to hormone biosynthesis, fatty acid metabolism, and PPAR signaling, indicating that 20E partially restored CAP-suppressed developmental and metabolic programs. Further analyses demonstrated that CAP exposure caused a sustained elevation of cytosolic Ca2+ levels, accompanied by attenuation of the 20E pulse, an abnormal increase of juvenile hormone (JH), and depletion of energy reserves and reducing equivalents, as reflected by reduced ATP, triglyceride, and NADPH levels. Exogenous 20E supplementation restored 20E signaling, promoted JH degradation, and partially alleviated Ca2+ overload; however, it also accelerated energy-store mobilization and further depleted energy reserves. Consequently, although metamorphosis was accelerated, whole-cocoon weight was not restored. In summary, this study proposes a mechanistic framework for CAP-induced developmental impairment: Ca2+ homeostasis disruption → hormonal dysregulation → metabolic exhaustion. Additionally, it clarifies the dual role of 20E-mediated rescue, providing insights for non-target risk assessment and sericulture protection.