Final answer:
The pre-pupa stage is an active larval stage with chewing mouthparts and no wings, while the pupa stage is inactive, often enclosed, and undergoing metamorphosis. The juvenile hormone regulates the transition from pre-pupa to pupa in insects.
Step-by-step explanation:
The visual differences between the pre-pupa and the pupa stages in insects are quite significant. During the pre-pupa stage, the larva may still be active, feeding, and resemble a larger version of its earlier stages, with chewing mouthparts and without wings. In contrast, during the pupa stage, the insect does not eat or move and is often enclosed within a cocoon or chrysalis. This stage is a period of intense transformation where the insect's body is reorganized into its adult form.
In complete metamorphosis, the adult insect that emerges after the pupal stage will look very different from its larval form. It may have different mouthparts, as in the case of butterflies whose larvae have chewing mouthparts and adults have sucking mouthparts. Additionally, adult insects generally have fully developed wings, which are not present in the larval stages. The juvenile hormone (JH) regulates these changes and determines when the larva will undergo metamorphosis into a pupa.