Recent advances in the mode of action of juvenile hormones and their analogs

Ecdysteroids (steroid hormones, 20 hydroxyecdysone, 20E, is the most active form) and juvenile hormones (JH, sesquiterpenoids) regulate almost every aspect of the insect's life including growth, development, immune response and reproduction. While 20E initiates and coordinates molting and metamorphosis, JH maintains the juvenile status and when the JH level goes down, it signals the insect to undergo metamorphosis (Riddiford 1994, 1996). Both 20E and JH along with other hormones regulate vitellogenesis, oogenesis, fertilization and choriogenesis during reproductive maturation of insects (Wyatt et al. 1996). In some insects such as the mosquito Aedes aegypti, 20E plays a critical role in the regulation of vitellogenin genes (Raikhel et al. 2002), whereas in others such as Locusta migratoria, JH plays a key role in the regulation of vitellogenin genes (Dhadialla and Wyatt 1983). In Drosophila melanogaster, 20E enhances the expression of some of the antibacterial peptides such as diptericin that are involved in the suppression of bacterial infection and JH suppresses this enhancement (Flatt et al. 2008). In Spodoptera exigua 20E enhances the sensitivity of plasmatocytes to an insect cytokine, plasmatocyte-spreading peptide whereas JH and JHA antagonize this enhancement (Kim et al. 2008). In addition, JH regulates other transformative processes such as diapause, migratory behavior, wing length, color polymorphism and caste determination (Futahashi and Fujiwara 2008; Giray et al. 2005; Hartfelder 2000; Hrdy et al. 2006; Min et al. 2004; Singtripop et al. 2000).