The term 'stage of metamorphosis' refers to the different stages that an insect goes through during its life cycle. The PUPA stage is the fourth stage of metamorphosis, in which the insect is in a resting state and undergoes dramatic changes in its body structure. During this stage, the insect's body is encased in a protective cocoon or chrysalis, and its organs and tissues are reorganized. After the PUPA stage, the insect emerges as an adult.