Abstract: 【Aim】This study aims to explore the effects of exogenous juvenile hormone (JH) on the female ovarian development and transcription levels of the reproduction-key genes of Spodoptera frugiperda.【Methods】Polyclonal antibody was prepared after isolation and purification of vitelline protein of female S. frugiperda. The vitelline protein contents in the 7-8-day-old female pupae and 1-10-day-old female adults of S. frugiperda were determined using indirect enzyme-linked immunosorbent assay (ELISA). The 5-day-old female pupae were treated with 25 μg/individual precocene, and the newly emerged female adults were supplemented with 100 μg/individual exogenous JH analogue methoprene. Subsequently, the preoviposition period, oviposition period, number of eggs laid per female and hatching rate were calculated. The 3-day-old female adults were dissected to observe the ovarian development, measure the ovarian length, and take photographs. Finally, the expression levels of genes of vitellogenin (Vg) and vitellogenin receptor (VgR) in the 3-day-old female adults of each treatment were quantified using qPCR.【Results】The vitellin content of S. frugiperda increased first and then decreased as female adult emerged, reaching its peak in the fat bodies at 1-day-old and ovaries at 4-day-old. Precocene treatment resulted in a downregulation of the endogenous JH in S. frugiperda, leading to obvious impediment of ovarian development compared to the normally reared female adults as the blank control group. Additionally, there was a significant reduction in the amount of ovarian eggs. However, exogenous supplementation of methoprene after the precocene treatment effectively restored normal ovarian development. The average ovarian length in the precocene treatment group was 39.89 mm, which was significantly shorter than that in the blank control group of 49.79 mm. The average ovarian length in the methoprene treatment group was 46.67 mm, and significantly longer than that in the precocene treatment group, but had no significant difference from that in the blank control group. The average number of eggs laid per female in precocene treatment group significantly decreased to 576.33 grains, as compared to that in the blank control group (1 128.37 grains), significantly decreased by 48.91%. The average number of eggs laid per female in the methoprene treatment group was 806.93 grains, which was significantly higher than that in the precocene treatment group. The expression levels of SfVg and SfVgR in female adults treated with precocene were significantly downregulated as compared to those in the blank control group, while methoprene significantly promoted the expression levels of SfVg and SfVgR.【Conclusion】The suppression of endogenous JH through precocene treatment significantly impeded female fecundity, hindered normal ovarian development, and reduced the transcription levels of SfVg and SfVgR in female adults of S. frugiperda. Conversely, exogenous JH supplementation effectively restored the female fecundity. This study further validates the crucial regulatory role of JH in the reproductive process of S. frugiperda and provides a theoretical foundation for future research on the regulatory mechanism of JH of female reproduction.

Key words: Spodoptera frugiperda, vitellogenesis, juvenile hormone, ovarian development, female reproduction