Since it was first postulated by Wigglesworth in 1934,juvenile hormone (JH)is considered a status quo hormone in insects because it prevents metamorphosis that is initiated by the molting hormone 20-hydroxyecdysone (20E).During the last decade,significant advances have been made regarding JH signaling.First,the bHLH-PAS transcription factor Met/Gce was identified as the JH intracellular receptor.In the presence of JH,with the assistance of Hsp83,and through physical association with a bHLH-PAS transcriptional co-activator,Met/Gce enters the nucleus and binds to E-box-like motifs in promoter regions of JH primary-response genes for inducing gene expression.Second,the zinc finger transcription factor Kr-h1 was identified as the anti-metamorphic factor which transduces JH signaling.Via Kr-h1 binding sites,Kr-h1 represses expression of 20E primary-response genes (i.e.Br,E93 and E75) to prevent 20E-induced metamorphosis.Third,through the intracellular signaling,JH promotes different aspects of female reproduction.Nevertheless,this action varies greatly from species to species.Last,a hypothetical JH membrane receptor has been predicted to be either a GPCR or a tyrosine kinase receptor.In future,it will be a great challenge to understand how the JH intracellular receptor Met/Gce and the yet unidentified JH membrane receptor coordinate to regulate metamorphosis and reproduction in insects.