Interactions between 20-Hydroxyecdysone and Juvenile Hormone I, II, and III during the Developmental Stages of Spodoptera frugiperda

Juvenile hormones (JHs) play a crucial role in the development of the fall armyworm, Spodoptera frugiperda, with varying types and concentrations observed at different stages. However, the interplay between JHs and 20-hydroxyecdysone (20E) in co-ordinating the life cycle of S. frugiperda remains unknown. In this study, by using high-precision UPLC-MS/MS and qRT-PCR, we detected changes in JH and 20E levels and identified important 20E receptor and response genes. Our findings revealed that JH I antagonises JH II, whereas JH II promotes JH III synthesis. High JH I and JH II concentrations in the larval stage strongly affected moulting to the next instar. Furthermore, these hormones inhibit 20E synthesis and reduce its receptor expression, thereby affecting 20E signalling. During pupation, JH II plays a crucial role in stimulating 20E synthesis for larval-pupal transformation. JH I and JH II are essential for eclosion, precisely controlling emergence timing and subsequent reproductive organ maturation. These hormones likely regulate larval development, pupation, and adult reproduction in S. frugiperda. Further studies are warranted to explore the regulatory advantages of JH I and JH II over JH III.