IIS/TOR network plays an essential role in ovarian development in the pupal stage of the fall armyworm, Spodoptera frugiperda

The ovary plays a crucial role in the female reproductive system of insects and is vital for the perpetuation of insect populations. The insulin/insulin-like growth factor signaling (IIS) and target of rapamycin (TOR) signaling network play a key role in controlling ovarian development and maturation during the adult stage. However, the pupal stage is a critical developmental phase in the reproductive system of holometabolous insects, and the regulatory role of the IIS/TOR network during this stage remains to be elucidated. In this study, we observed that during the pupal stage, the enlargement of ovarian development was accompanied by a corresponding increase in messenger RNA expression levels of genes within the IIS/TOR signaling pathway and insulin levels in the hemolymph. Decapitation experiments, serving as a pivotal approach to assess the regulatory role of the IIS signaling pathway in ovarian development, demonstrated that decapitation markedly inhibited ovarian development at this critical stage. Exogenous insulin administration significantly increased the phosphorylation levels of FOXO, S6K, and 4E-BP, thereby enhancing ovarian development and resulting in significant elongation of the ovarioles. In contrast, the injection of IIS/TOR pathway inhibitors, LY294002 and Rapamycin, reduced the phosphorylation of these proteins, inhibiting ovarian development during the pupal stage and leading to a significant shortening of the ovarioles, negatively impacting the reproductive performance of adult females. The current findings indicate that the IIS/TOR signaling network significantly regulates ovarian development during the pupal stage of Spodoptera frugiperda, providing new molecular insights for the development of pest management strategies.