Integument

The integument is the external layer of tissue that covers the outer surface of insects and the surfaces

of the foregut and hindgut. It is composed of the epidermis, which is a continuous single-layered

epithelium, and an underlying thin basal lamina plus the extracellular cuticle that lies on top of the

epidermis.

Functions of the integument

1.Protection of internal organs and tissues.

2.Protective barrier against entry of pathogens, parasites, predators and pesticides.

3.Preventive barrier against water loss.

4.Provides for the insect the sensory “windows to the outside world”

5.Lines the tracheae, tracheoles, salivary glands and portions of reproductive tract. At

the molt, all of this is shed and grow it again.

6.Protective barrier for foregut and hindgut.

Major layer of cuticle and epidermal layer

Epicuticle

Exocuticle

Endocuticle

Pore canals

Hypodermis or epidermis

Basement membrane or basement envelope (Basallamina)

Sense organs

Oenocytes

Integument glands

Epicuticle: Complex layer. The outermost layer and probably the most important layer.

Water proofing and general impermeability of cuticle. Produced by

hypodermis/epidermis and dermal glands.

Cement layer-Thin outside layer. Closely associated with wax layer and may serve to

protect it. Not found in all insects.

2. Wax layer-Hydrocarbons constitute 90% of this layer. Important to insects for water

loss, thus waterproofing of cuticle. In some insects (e.g., Fulgoridae and scales), the

insects produce a large bloom of wax on outside. Bees have special glands, wax

glands, on ventral abdominal segments 4-7 that produce wax, which is then formed into

flakes used by the bees to make their cells.

Exocuticle: Region in which cross-linking of proteins occurs to give cuticle hardness.

Region not broken down by proteases at molt and is what usually remains in form of

exuviae. Melanin and other pigments found in this area. Sclerotization mainly occurs

here. Also arthropodin and sclerotin.

Endocuticle: That region directly above the hypodermal cells. Is continually being

synthesized (in a dark/light way-24 hrs) and often is laid down in layers, thus can often

be used to age-grade someinsects. Contains most of the chitin, which is broken-down at

the molt by chitinase. Little cross-linking of proteins, thus most is broken-down at

molting and reabsorbed. In soft-bodied insects and regions of flexibility (eg. Arthrodial

membranes orintersegmental membranes), this layer is well developed and not the

exocuticle.

Pore canals:Narrow pores that extend from the hypodermalcells to the inner most part

of the epicuticle. Believed to beinvolved in transport of lipids from hypodermal cells to

theepicuticle or outer layer

Hypodermis or epidermis: A single layer of cells that underlies the cuticle and is

responsible for its production. It is the only living portion of the integument that is

ectodermal in origin. These cells can be modified to form dermal glands, sensory

receptors and oenocytes.

Basement membrane or basement envelope (Basallamina): Mucopolysaccharide

layer that is secreted by the hemocytes, is penetrated by nerves and tracheae going to

hypodermis, and is a selective barrier between hemolymph and epidermal cells.

Hormones and other nutrients can passthrough this selectively permeable layer to reach

thehypodermal cells. Is important in the recognition of ‘self’;thus, the insect’s blood cells

do not recognize it as ‘foreign.’Molecules in this layer are charged and probably act like

amolecular sieve.

EPIDERMAL CELLS

The epidermal cells are attached to the basal lamina by hemidesmosomes, which anchor the cell

membrane to collagen fibers in the basal lamina. Near their base, the cells are attached to each

other by desmosomes; near their apical end, they are attached to each other by a narrow,

impermeable zone (the adhering zonule), effectively separating the cuticular compartment from

the lateral space between cells. Below the zonule are bands of septate desmo-somes, which may

be adhesive, and gap junctions through which the cells can communicate chemically with each

other by interchange of low-molecular-weight compounds.

The cuticular materials (chitin and proteins) are secreted from the apical surface of the epidermal

cells into the subcuticular space, or deposition zone, where they are assembled into an intact

cuticle. The apical surface is folded into shorter or longer microvilli, depending on the stage of

the molting cycle and the secretory activity of the cells.