What term describes an immature insect stage between the larva and adult?

The term that describes the immature insect stage between the larva and the adult is "Pupa." This stage is critical in the life cycle of many insects, particularly those that undergo complete metamorphosis, such as butterflies and beetles. During this period, the insect is typically inactive and undergoes significant transformation, reorganizing its body structure to transition from the larval stage to the adult form.

Some insects, like butterflies, transform from a caterpillar (the larval stage) into a pupa, commonly referred to as a chrysalis in the case of butterflies. Other insects may develop into a pupa without the chrysalis stage, but all utilize the pupa phase for development into adults.

The option of "Caterpillar" refers specifically to the larval stage of butterflies and moths, not the transitional pupal stage. "Nymph" describes a stage in insects that undergo incomplete metamorphosis, such as grasshoppers and cockroaches, where the young resemble smaller versions of the adult rather than entering a pupal phase. Therefore, the pupa effectively encompasses the correct definition of this developmental stage in the life cycle of an insect.