Figure 1.5.

Checkpoint controls of developmental timing of metamorphosis. The figure shows a proposed model for checkpoint control of ecdysone release and timing of pupariation. Accumulation of nutrients corresponding to the critical weight presumably results in the insulin dependent production of the critical weight ecdysone peak 8 h after L3 ecdysis. Maturation and patterning of the imaginal disks and the photoperiod are also verified by the endocrine system before development can proceed. These checkpoints may potentially translate into to the other low-level ecdysone peaks 20 and 28 h after L3 ecdysis. When all checkpoints are cleared, developmental transition to the metamorphic stage can take place.