Abstract: Ecdysteroids (Ecd) and juvenile hormones (JH) play critical roles in regulating insect development and (metamorphosis. Though the molecular mechanisms of Ecd action are well understood now, those of JH action, in contrast, are still poorly known mostly because the JH receptor has not been successfully identified yet. In this review, we described three aspects of recent progresses in molecular mechanisms of JH action. 1. JH and Ecd cross-talk with each other at the molecular level. JH modulates or suppresses Ecd signal to regulate insect development and metamorphosis. 2. Met and USP are two potential JH nuclear receptors. 3. JH also transduces signal via membrane receptor and protein kinase C.

Key words: Juvenile hormone, ecdysteroids, juvenile hormone receptor, methoprene-tolerant protein (Met), ultraspiracle (USP), protein kinase C (PKC)