The third or penultimate stage in the life cycle of a holometabolous insect.
In mosquitoes, the pupal-adult apolysis occurs shortly after the larval-pupal ecdysis. Hence, there is a very short exposed pupal period, perhaps one to four hours, followed by a very long pharate adult phase, perhaps about 44-47 hours of the two days that so many species are conventionally said to be in the "pupal stage". So most of the conventional "pupal stage" is an adult, not a pupa, enclosed by the remains of the pupal cuticle. For this reason, most recent authors have adopted terms for parts of the pupal "skin" that include the words "sheath", "case" or "plate" because the parts cover or enclose the corresponding structure in the developing adult, e.g. scutal plate, which was recommended for use by Knight (1971b), overlies the adult scutum. There are, however, particular objections to using "plate" with terms for cuticular structures which are sclerites since sclerite and plate are so often used interchangeably. And of course, the scutum is a sclerite, so it is ambiguous to say "scutal sclerite" or "scutal plate". Then too, the pupa has a scutum which lies over the area in which the adult scutum will develop, but the adult scutum does not do any developing (being a sclerite and thus part of the cuticle) at all until after the apolysis marking the end of the pupal stage. Of course, when there is no longer a pupa as such, there is still the pupal "pelt" around the adult stage, and then the pupal scutum overlies the developing adult scutum. Would the pupal scutum be called the scutum before apolysis and the "scutal plate" after apolysis? Of course not, and for this reason terms which have included the words sheath, shield, case,
plate, pouch or sac are not recommended for use. If such terms were to be adopted, then logically the conventional pupal abdomen would have had to be dubbed the abdominal case, the genital lobe dubbed the genital case, etc.