20‐Hydroxyecdysone regulates pupal fatty acid metabolism, maintaining lipid metabolic homeostasis in <i>Chilo suppressalis</i>

Fatty acids are important intermediates in lipid metabolic pathways, and fatty acid metabolism is a complex process. As one of the hormones regulating insect lipid metabolism, the precise regulatory mechanisms of 20-hydroxyecdysone (20E), particularly its relationship with fatty acid metabolism, remain unclear. Using the rice pest Chilo suppressalis as a model, we investigated the effects of 20E on fatty acid metabolism in the fat body during the pupal stage. Our study found that high levels of 20E disrupts normal fat body development during the pupal stage, resulting in reduced expression of lipid metabolism-related genes. Lipidomic analysis revealed that 20E induces fatty acid accumulation in the fat body. Transcriptomic analysis indicates that differentially expressed genes are enriched in the fatty acid synthesis pathway. These genes are highly expressed during the late pupal stage, which correlates positively with the development of C. suppressalis female pupae. After knocking down C. suppressalis fatty acid synthase (CsFAS) and C. suppressalis fatty acyl-CoA reductase (CsFAR), we observed increased levels of triglyceride and free fatty acids in the fat body, along with evidence that 20E inhibits the expression levels of CsFAS and CsFAR. Our study indicates that 20E regulates lipid metabolism during the pupal stage by suppressing the transcription levels of key metabolic genes, CsFAS and CsFAR, in the fatty acid metabolism pathway. This helps to better understand how hormones regulate lipid metabolism in the insect fat body and suggests that the discovery of FAS and FAR may provide new molecular targets for pest control.