A FoxO-Autophagy-Lipid Mobilization Axis Regulates Fat Body Remodeling During Honeybee Metamorphosis

Forkhead box O (FoxO) transcription factors act downstream of insulin signaling and play conserved roles in development and metabolic homeostasis in insects. However, whether FoxO participates in 20-hydroxyecdysone (20E)-mediated pupation and fat body remodeling in honeybee larvae remains unclear. Here, we show that FoxO is highly expressed during the prepupal and pupal stages of honeybee development. RNA interference (RNAi)-mediated silencing of FoxO delayed pupation, inhibited ecdysteroid biosynthesis and 20E signaling, and ultimately led to pupal lethality. Knockdown of FoxO also suppressed the expression of lipolytic genes, reduced lipase activity, and increased triglyceride (TG) accumulation in the fat body. Furthermore, FoxO deficiency impaired autophagy, as evidenced by reduced LysoTracker staining, decreased autophagosome formation, and downregulation of Atg genes. These findings demonstrate that FoxO participates in 20E-induced pupation of honeybee by regulating the expression of key genes involved in 20E biosynthesis and the 20E signaling pathway. FoxO coordinates autophagy and lipid mobilization in the fat body to provide energy for pupal development. Collectively, our results establish FoxO as a central regulator linking endocrine signaling, energy metabolism, and tissue remodeling during honeybee metamorphosis.