Insect Anatomy: Body Plan & Exoskeleton

Insect Body Plan

•Insects consist of  cylindrical body containing visceral organs and series of ventro-lateral limbs

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•Segmentation is a key characteristic of all insects

Segmentation

•Insects evolved from segmented ‘worm like’ ancestors

•All arthropods are defined by segmented bodies, joints and limbs

•Segments reduced and fused over evolutionary time

•Adapted to specific functions

Insect Body Plan

•Tagma (plural tagmata) are groupings of segments which have a shared function

•Insects: the head, thorax, and abdomen

•Internal organs are not segmented

The Insect Head

•Feeding appendages and most important sense organs

•Detects changes in odor, color, moisture, sounds and touch

•Contains brain

The Thorax

•Second body segment is thorax

•Modified for locomotion

•Includes wings and legs: for insects that fly long distances a lot of nutrient reserves dedicates to these muscles

Legs

•Each pair of legs has same general structure but are modified for different functions

Modification: Bee

•Legs of certain bees are used to collect pollen

•Have a pollen basket or long setae (plumose hairs) on hind legs

The Abdomen

•Last body division containing visceral organs

•Includes

•Most of the alimentary canal

•Dorsal circulatory vessel

•Excretion organs

•Reproductive organs

• •Segments contain spiracles: openings to the environment for gas exchange

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  •May have modified organs for reproduction: genital segments

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  •Primitive groups may have cerci

Cerci

•Paired appendages at end of abdomen

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•Some are sensory and others used in copulation or defense

Ovipositor: Females

•Females may have modification of ovipositor: used to deposit eggs

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•Many groups have adaptation for stinger

The Exoskeleton

•Hardened, jointed cuticle that covers the body

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•Functions:

•Support of muscles

•Barrier for water loss & disease elements

•Predators are mechanically prevented and avoided through coloration

•Determines the form and size of insect

Chitin

•Characteristic polysaccharide that is the major constituent of insect procuticle

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•Becomes hard and rigid (sclerotized) to form the exocuticle

The Exoskeleton

•Integument provides basis for exterior skeleton that distinguishes arthropods

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•Three basic components:

1. Tough outer non-cellular cuticle

2. A single layer of cells: epidermis

3. Inner sheet of connective tissue: basement membrane

Procuticle: Exo & Endocuticle

•Proteins differ between body places and life stage

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•One protein associated with rigid cuticle, another with flexibility, another with elasticity

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•Rubber-like protein is called resilin may occur in special places; elasticity used in wing articulations

The Epidermis

•Epidermal cells organized in a single layer with microvilli surface for cuticle secretion

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•At base, cells border noncellular basement membrane, which acts as barrier between epidermis and hemolymph

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•Pore canals transport secretions
to the procuticle during molting

Production of Color

•Most colors are produced in cuticle

•Both cuticle and deeper tissues may contribute to production of color patterns

•White light composed of various wavelengths, when insect absorbs all but red, we see red

•Due to physical structure of object

•Chemical compound absorption

Phasmatodea

•Change color between day and night

•Color change related to movement of pigment granules in epidermis

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When clustered they give a pale color between day and night

Pigmentary Colors

•Range of chemical compounds that serve as pigment

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•Excretory products no longer used in biochemical pathways

•Pigments may be absorbed by the food

Structural Colors

•Physical shape and thickness of cuticle can produce colors

•Interference

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•Iridescence caused by differential refraction of light waves

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•Changes as the angle of view changes

Blue Morpho Butterfly

•Blue of Morpho Butterfly arises from a series of vertical vanes on each scale

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•No blue pigments: structural coloration

Helicoidal arrangement

•cuticle produces iridescent metallic coloration in beetles and flies

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•Changing angles from previous layer makes colors appear