Insect Integument and Metamorphosis

 Introduction to integument and its importance

An insect's body wall is known as an Integument or Exoskeleton. It is rigid, flexible, lighter, and stronger, and has been modified in various body parts to suit various modes of life. The unique properties of insects' outermost layer contribute to their success. The cuticle, a chitinous apical extracellular matrix secreted by the epidermis, covers a single layer of ectodermal cells. Epidermal cells are also involved in the formation of the basement membrane, a basal extracellular matrix that effectively separates the integument from the hemocoel. The exoskeleton largely determines an insect's outer shape and serves as an exoskeleton to which the muscles are attached. It serves as a sensory interface with the environment and protects insects from a variety of threats such as mechanical damage, radiation, desiccation, and pathogenic microorganism invasion. The integument covers almost all of the insect body's outer surfaces, including ectodermal invaginations such as the oral cavity, hindgut, lower genital ducts, and many glands.

Structure of Integument

The body wall is made up of three layers: an inner cellular layer (Epidermis or Hypodermis), an outer non-cellular layer (cuticle), and a basement membrane.

Epidermis

It is a unicellular layer composed of polygonal cells that molt into cuboidal or columnar shapes. These cells have a well-developed nucleus as well as other cytoplasmic contents. Certain cytoplasmic processes hold adjacent epidermal cells together. During molting, all epidermal cells are glandular and secrete cuticles, and enzymes are involved in the production and digestion of old cuticles. Based on the function they perform, epidermal cells differentiate into the following types and may modify into

1.      Dermal glands

2.      Trichogen cell

3.      Molting glands

4.      Peristigmatic glands

Cuticle

It is the outermost thick layer of integument secreted by the epidermis. It is divided into two-layer

•       Epicuticle
•       Procuticle

 The epicuticle is the very thin outermost layer. The exocuticle's pore canals aid in the deposition of the epicuticle. This layer is divided into four sections: the cement layer, the wax layer, the polyphenol layer, and the cuticulin layer. Procuticle: After sclerotization, it is divided into Exocuticle and Endocuticle. Exocuticle is sclerotized, hard, and darkly pigmented. It provides rigidity to the cuticle and is made up primarily of chitin and a hard protein known as sclerotin. The endocuticle is soft, white, and unsclerotized. It has more chitins but no sclerotin, a hard protein.

Basement Membrane

It is a non-living amorphous granular layer of the integument that forms the basal part of the body wall from degenerated epidermal cells. It has a thickness of about 0.5 and is made up of fibrous proteins and glycosaminoglycan polymers of disaccharides. The basement membrane forms a continuous sheet beneath the epidermis where muscles are attached and merge with the muscle sarcolemma.

What is Metamorphosis and its Importance

Metamorphosis is defined as the rapid and complete transformation of an immature larval life to a sexually adult form that involves changes in morphology, function, and habitat. Metamorphosis can result in changes to the organism's entire body plan, such as a change in the animal's number of legs, mode of eating, or mode of breathing. One advantage of metamorphosis may be its ability to reduce competition. Pre-metamorphic animals typically consume very different resources than their adult counterparts. Caterpillars eat leaves, while butterflies feed on nectar. Older members of the species are effectively barred from competing with younger members. This could lead to more members of the species reaching sexual maturity without fear of being outcompeted by older members of their species.

Complete Metamorphosis

A larva undergoes a complete metamorphosis when it completely changes its body and prepares to become an adult. The butterfly is the most well-known example, beginning as a worm-like, leaf-eating caterpillar and evolving into a flying, nectar-drinking creature with an exoskeleton. Because the caterpillar's transformation is so rapid and incomplete, it must spin a cocoon and lay dormant for weeks while its body undergoes radical changes. Eggs, larvae, pupae, and adults have completed their metamorphosis. Beetles, flies, moths, ants, and bees are examples of animals that change from a worm-like larval stage to a completely different animal.

Incomplete Metamorphosis

Only a portion of the animal's body changes during incomplete metamorphosis. Hemimetabolous animals are those that only change their bodies partially as they mature. Cockroaches, grasshoppers, and dragonflies, for example, hatch from eggs that resemble their adult counterparts. They do grow wings and reproductive organs, but they do not completely remake their bodies like their completely metamorphosing cousins. It is clear from the egg, nymph, and adult stages of incomplete metamorphosis that insects that have progressed from primitive Lepisma-like forms have begun to explore two types of environments. However, such attempts are only successful in forms that have undergone a complete metamorphosis.