Endocrine events during Drosophila metamorphosis. Timeline illustrates changes in ecdysteroid levels during the larval-pupal-adult transformation at 25°C. The late larval (LL) pulse of 20-hydroxyecdysone (20E) triggers pupariation, with subsequent development timed by hours after puparium formation (h-APF). The prepupal (PP) pulse at approximately 12 h-APF triggers pupation; the pupal (P) pulse drives development of the adult fly. Emergence of the adult (eclosion) occurs at approximately 96 h-APF. Open arrow indicates when neuronal cultures were prepared (8 h-APF; see Results). Filled bar shows period when abdominal RP2s undergo PCD (approximately 14 to 20 h-APF; see Results). Adapted from  based on hormone titers from [7, 72].