Which stage is NOT part of the gradual metamorphosis process?

In the context of insect development, gradual metamorphosis, also known as hemimetabolous development, consists of a series of stages that do not include a pupal stage. In this process, insects typically progress through three main stages: the egg, nymph, and adult.

The egg is the initial stage where the insect begins its life cycle. Once it hatches, the insect emerges as a nymph, which resembles a smaller version of the adult but lacks fully developed wings. This nymph stage continues to mature, undergoing a series of molts until it reaches the adult stage, where it is fully developed and capable of reproduction.

The pupa stage is characteristic of complete metamorphosis (holometabolous development), where insects undergo a transformation into their adult form, often resulting in significant changes in body structure. Since gradual metamorphosis does not involve a pupa stage, this option stands out as the one that does not fit within this particular developmental process.