Figure 3.

Environmentally sensitive developmental thresholds in the second and third instar as defined in Drosophila. Toward the end of the second instar, a size-dependent threshold called threshold size for metamorphosis determines whether the following molt will be the final larval molt before metamorphosis. The precise timing for this event has not yet been determined. At the beginning of the third instar, environmentally sensitive thresholds control the transition to metamorphosis. Minimal viable weights for pupariation and eclosion are the minimal sizes above which larvae can survive starvation to metamorphose and to eclose to adults respectively. Critical weight, also referred to as critical size, is the minimal size at which the onset of metamorphosis can no longer be delayed by starvation.