Which of the following organisms does not undergo incomplete metamorphosis?

Butterfly does not undergo incomplete metamorphosis. Incomplete metamorphosis is a type of metamorphosis in which an insect hatches from an egg into a nymph, which then goes through a series of molts until it reaches adulthood. The nymphs look similar to adults, but lack wings and reproductive structures. Butterflies, on the other hand, undergo complete metamorphosis, which involves four distinct stages: egg, larva (caterpillar), pupa (chrysalis), and adult. In the larval stage, the caterpillar looks very different from the adult butterfly, and during the pupal stage, it undergoes a dramatic transformation before emerging as an adult butterfly with wings and reproductive structures. Therefore, the correct answer is butterfly as it undergoes complete metamorphosis, unlike locust, grasshopper, and cockroach which undergo incomplete metamorphosis.