Ecdysone induces molting and metamorphosis, as well as regulating the timing of development in insects, whereas the IISTORC1 signaling pathway integrates growth factors, nutrition and energy to control growth rate. Interplay between these two pathways occurs in three ways: (1) IISTORC1 signaling activates ecdysone synthesis in the prothoracic gland; (2) ecdysone inhibits both IISTORC1 signaling and transcription of Myc in fat bodies. In other words, ecdysone inhibits systemic IISTORC1 signaling by inhibiting tissue growth and the endocrine function of fat bodies; (3) activated insulin signaling inhibits ecdysone signaling by inhibiting transcription of DOR, which is regulated by the transcriptional activity of FOXO. Thus, the interplay between ecdysone signaling and IISTORC1 signaling allows the coordination of growth rate and developmental timing, thereby determining final body size.