Peggy K. Powell, Ph.D.
Board Certified Entomologist February, 1995
There are several types of metamorphosis in the insect world, ranging from no apparent metamorphosis, with only a change in size and sexual maturity, to complete metamorphosis, with quite drastic changes in both appearance and feeding habits. Both the type of metamorphosis and the developmental stage of an insect should be considered when designing a pest management program.
Metamorphosis means "change in form". Most insects undergo this change, sometimes along with a change in habits and needs, to a greater or lesser degree, at some point in their lives. The change occurs during molting, when the exoskeleton becomes too small, splits, and is shed.
Insects with simple metamorphosis have three life stages: egg, nymph, and adult. These insects may have wings which, if present, develop externally. Young are known as nymphs and there is no resting stage. Insects with simple metamorphosis can be further broken down into those with no (or no apparent) metamorphosis, those with incomplete metamorphosis, and those with gradual metamorphosis.
In the case of insects with complete metamorphosis (holometabolous insects), the wings, if present, develop internally. The active immature stages are known generally as larvae. In some orders, larvae are referred to by other names, such as maggots (flies), caterpillars (butterflies and moths), or grubs (beetles). These insects also have a resting stage known as a pupa.
Insects with complete metamorphosis include lacewings (Order Neuroptera), beetles (Order Coleoptera), caddisflies (Order Trichoptera), butterflies and moths (Order Lepidoptera), flies (Order Diptera), fleas (Order Siphonaptera), and sawflies, ants, wasps and bees (Order Hymenoptera).
Larvae and adults of insects with complete metamorphosis live in very different habitats and often feed on different types of food. The different life stages of a single pest species may therefore require vastly different management strategies. In many cases, only one stage may be a damaging pest. Larvae of insects with complete metamorphosis usually have chewing mouthparts; many are pests of various crops.
A few insects exhibit intermediate types of metamorphosis, types that don't fit any of the above descriptions. Thrips and whiteflies fall into this intermediate group. Thrips pass through two nymphs stages, in which the nymphs feed on the same food as the adults. Next are prepupal and "pseudopupal" stages, before the insect molts to the adult stage. Whiteflies, even though considered to have gradual metamorphosis, pass through a pupal or resting stages before molting to the adult.
In the case of insects with complete metamorphosis, it is as if one species is represented by two or three completely different animals with different needs and habits. Control of insects with life stages having vastly dissimilar feeding habits require different management techniques. The larvae feed and live in one habitat and may leave that area to molt to the pupal stage. The adult may occupy an entirely different habitat and return to the larval feeding site only t lay eggs.
For example, house fly maggots often can be controlled through manure management, whereas the adult house fly is better managed through the use of exclusion devices or foggers. Similarly, the southern corn rootworm and its adult stage, the spotted cucumber beetle, require different scouting techniques and different management strategies. In the case of many insects with gradual metamorphosis, (e.g., the potato leafhopper) both nymphs and adults occupy the same habitat, feed on the same foods, and therefore generally require the same scouting and management techniques.
Program and activities offered by the West Virginia University Extension Service are available to all persons without regard to race, color, sex, disability, religion, age or national origin. Issued in furtherance of Cooperative Extension Work, actrs of Congress of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Rachel B. Tompkins, Director, Cooperative Extension Service, West Virginia University.