In Manduca sexta, the molting process is initiated when larvae attain a set size, the critical weight. Although the critical weight phenomenon is well documented, the physiological event that initiates the molting process is not known.
Hypothesis: During the intermolt period, the tracheal system is fixed in size, which puts an upper limit on the rate of oxygen supply. Metabolic demand for oxygen increases with body size, so oxygen supply could become inadequate beyond a certain size. Lack of oxygen might therefore trigger the molt, during which the old tracheal system is shed and replaced with a new larger one.
Approach:
1) Create a mathematical model to formalize this hypothesis. Predict the shift of critical weight and the timing of the molt under different oxygen concentrations.
2) Confront the predictions to data of Manduca sexta larvae reared under different oxygen concentrations.