E35 Growth and molting

Topic

This molt—the insect's final ecdysis—constitutes the process by which the insect replaces its exoskeleton to grow, as the rigid cuticle cannot expand continuously along with the insect's body.

The insect's ecdysone hormone triggers both the separation of the old epicuticle and the synthesis of the new cuticle.

During the expansion following the molt, the new cuticle is soft; consequently, the insect utilizes hemolymph pressure to expand until it reaches its new body size.

Arrhenius's law predicts the time required for sclerotization (hardening) based on the ambient temperature: an insect in a cold climate requires significantly more time to sclerotize its new cuticle—a period during which it remains vulnerable to external predation. Colder climatic conditions result in a longer sclerotization time for the new cuticle (in accordance with Arrhenius's law), thereby prolonging the period of vulnerability to predation.

The glass transition temperature—described by the Fox equation—determines the specific temperature at which the cuticle shifts from elastic behavior to a distinct glassy state. Consequently, this model—based on the replacement of the exoskeleton—allows Huxley’s concept of allometric growth to describe how each distinct part of the insect's body grows at its own unique rate between successive molts; this results in a final change in form that constitutes the fundamental basis of the insect's metamorphosis. The fact that the insect undergoes a greater number of these successive molts means that the cumulative change in form across its various body parts becomes even more pronounced.

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