What term refers to the developmental stage where significant changes occur in insects with complete metamorphosis?

The developmental stage where significant changes occur in insects with complete metamorphosis is called the pupa stage. During this phase, the insect undergoes a transformation from larva to adult. This process, known as metamorphosis, includes substantial internal and external changes, as the larval structures break down and new adult features are formed. The pupa is often a quiescent stage where the insect is not feeding and is usually enclosed in a protective casing, allowing essential processes to take place without external disturbances. This stage is critical for the insect's development as it transitions into its final adult form, which is crucial for reproduction and the continuation of the species.

The egg stage is where the insect begins its life cycle and does not involve significant morphological changes. The larva stage is characterized by growth and feeding, but it is during the pupa stage that the most dramatic changes occur that prepare the insect for its adult life. The adult stage is the final stage of development after the changes in the pupa are complete. Thus, the pupa stage is rightly identified as the phase of significant transformation during complete metamorphosis.