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Cockroach.

Periplaneta americana.

Systematic position

Phylum…..................Arthropoda

Subphylum……………Mandibulata

Class……………………..Insecta

Order……………………Orthoptera

Genus………………….Periplanata

Species………………. americana

Habit and Habitat

Cockroach is found in damp places and generally found in kitchens, bathrooms, sewage, grocer shops, etc., where food is available. It is a nocturnal animal hiding in holes and crevices during the day.It are omnivorous in diet. It is a fast runner i.e., cursorial in habit. It is diocious and oviparous and exhibits parental care.

External Features

Shape, Size and color. Its body is narrow, elongated and compressed dorso-ventrally and bilaterally symmetrical. The adult cockroach measures 2-4 cms in length and 1 cm in width. The color is reddish brown.

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Exoskeleton. The entire body of cockroach is covered by a hard brown colored exoskeleton.The exoskeleton of each segment has four separate sclerites which are joined together by delicate elastic articular membrane.The sclerites of dorsal side are called tergite,of ventral are called sternite and those at the lateral side are called pleurites.The exoskeleton consists of thick and strong chitinous cuticle which provides protection to body,prevents unnecessary water loss and points for the attachment of muscles.

Segmentation. It shows clear cut segmentation in its body except head. The thorax consists of three segments and abdomen ten segments in adults which were eleven in embryo. The head is said to be formed by the fusion of six embryonic segments. However the total body segments in embryo remain twenty but in adult only nineteen as said above.

Division of body. Its body is divisible into three regions i.e., head, thorax and abdomen.

Head.It is ovate and flattened antero-posteriorly and lies at right angle to the longitudinal body axis. It is highly mobile in all directions due to flexible neck. It is formed by fusion of six segments. The tergites of these segments have fused to form a head capsule.The head bears a pair of compound eyes , a pair of antennae and appendages around the mouth. The top of the head capsule is called the vertex. Below the vertex is a frons anteriorly which has a ventral clypeus.The sclerite of the head capsule forming vertex is called occiput and the lower part of the clypeus forms the upper lip or labrum.On the sides of the head capsule is a gena below each compound eye.At the back of the head is a large triangular occipital foramen which connects the cavity of the head with that of the body.

A Pair of kidney shaped sessile compound eyes are situated at the dorso- lateral sides of the head.In the angle between the eyes and the antennae are two small pale colored spots or fenestrae,they are under developed ocelli.A pair of antennae arise from membranous sockets,one on either side below the eyes. Each antenna has three parts, a large basal scape,followed by small pedicel and a long filamentous, many jointed flagellum.Such an antenna is called filiform antenna.The antennae posses small sensory bristles and it can be moved in all directions.The antennae belong to second segment of the head.

Mouth parts.The appendages around the mouth constitute mouth parts which are of chewing or mandibulate or orthopterous type.The mouth parts consists of a labrum, a pair of mandibles, a pair of maxillae, a labium and hypopharynx.

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1. Labrum.It is a membranous flat lobe suspended below the clypeus.It is movable due to the muscles inserted on its base. It lies in front of the mouth as the upper lip. On its ventral surface many sensory setae are situated which are possibly gastroreceptors. Fused to the inner surface of labrum is a membranous plate called epipharynx.

2. Mandibles. These are suspended from the sides of the head capsule, one on either side of the mouth. Each mandible is stout ,heavily sclerotised having teeth-like cutting plates at its inner edge.The mandibles are jaws used for crushing and cutting the food.The mandibles are movable by the contraction and relaxation of adductor and abductor set of muscles.The mandibles belong to fourth segment of the head.

3. Maxillae. These are two one on either side of the head capsule behind the mandibles.These are also attached to the head by muscles.Each maxilla has a basal protopodite having cardo and stipes prodomeres bent at right angles to each other.The cardo joins the maxilla with the head capsule.From the outer surface of stipes arises a five jointed maxillary palp representing exopodite,at the base of

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which is a small scelerite called the palpifer.From the inner side of the stripes arises a double outgrowth consisting of an outer hood like glea and inner lacinia which is flat, tapering lobe ending in two sharp claws-like projections,its inner margin bears stout bristles. The maxillae hold food by the claws of the lacinia and bring to the mandibles for mastication. The maxillae are also used for cleaning the antennae,pals and front legs. The maxillae belong to the fifth segment of the head.

4.Labium.It is the lower lip lying behind the mouth and represents second pair of maxillae which have fused together into one.It has a proximal postmentum divided into a large submentum and a small sceleterised mentum.The distal part of the labium is a paired structure and on each side it has 3-jointed labial palp,at the base of each palp is a small sclerite the palpieger.Between the labial palps are four lobes,two median are smaller glossae and two outer and larger paraglossae.The labial palps are sensory and labium does not take active part in feeding,but glossae and paraglossae together called ligula prevents the loss of food particles from the mandibles.The labium belongs to the sixth segment of the head.The first and third segments have no appendages.

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5. Hypopharynx.Between the maxillae and in front of labium is flat cylindrical structure called the hypopharynx or lingua.The common salivary duct opens at the base of the hypopharynx.

Neck. The neck or cervicum is a slender soft region supported by chitinous cervical plates,two dorsal and two ventral. The neck has muscles which retract and protract the head and turn it up or down or from side to side.The cockroach can also stretch its head like other insects.

Thorax. The thorax consists of three segments ,the prothorax,mesothorax and metathorax.Each segment bears a pair of walking legs and the first pair of wings arise from mesothorax,while the second pair from metathorax.The prothoracic segment is the largest and due to the presence of three pairs of walking legs it is also called as hexapoda.

Walking legs. All the three pairs of legs are similar and help the cockroach in its cursorial(fast running) habit.Each leg consists of five segments-a large basal coxa articulating with the thoracic segment between the pleuron and sternum,coxa is followed by a smaller trochanter which is freely movable on the coxa but is fixed to the next segment,the femur which is long and broad;this is followed by a long uniformly thick tibia which bears stout bristles the tibial spurs ; the last segment is tarsus having five movable joints or podomeres or tarsomeres which have five bristles and their lower sides have soft adhesive pads ,the plantulae.The last tarsomere of tarsus are often referred to as pretarsus and it terminates in two curved claws or ungues. Between the claws is a soft hollow lobe ,the arolium having small bristles.The arolium is an adhesive organ for holding on smoothsurfaces.

Wings. As mentioned earlier ,the first pair arises from mesothorax and second pair from metathorax.The wings are attached to the antero lateral margin of the notum.The first pair of wings are highly sclerotised and are known as elytra or tegmina.These are protective and cover the hind wings in folded stae,the left tegmen partly overlaps the right.The second pair of wings are membranous and larger,they lie folded below the tegmina when at rest.The wings are formed as outgrowths of the integument from between notum and pleuron.Each wing has two membranous layers with tubular and chitinous prologations of haemocoel between them known as veins or nervures which contain blood in early stages.Veins are strongly chitinised and enclose asmall trachea;the larger veins also contain anerve fibre.The cockroach has poorly developed wing muscles yet it can fly fairly well.

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Abdomen. Abdomen consists of ten segments. The exoskeleton of abdomen is formed of hardened sclerites.A typical abdominal segment has a dorsal tergum,ventral sternum and between them a narrow membranous pleuron on each side. Dorsally the abdomen has ten terga,but the 9th tergum of male and 8th and 9th terga of the female are largely covered by the 7th tergum.The 10th tergum is shield shaped with a deep cleft posteriorly .The 10th tergum bears a pair of long,tapering anal cerci which is fifteen jointed.Each circus is traversed by a nerve it bears a sense organ which is receptive to sound.Ventrally there are nine sterna in the male but only seven are visible externally in the female.The ninth sternum of the male has a pair of slender anal styles which are absent in the female in which the 7th sternum is produced backward into a pair of large apical lobes or gynovavular plates which form a keel -like structure.This rounded keel at once distinguishes the female from the male.The 8th and 9th sterna of the female have been invaginated inwards to form a chamber like gynatrium whose posterior part constitutes the oothecal chamber because ootheca or cocoons are formed in it. In the male a group of genital structures may slightly project from the end of the abdomen.The genital apertures of both the sexes are surrounded by sclerites called gonapophyses.In the male ,the gonapophyses belong to the 9th segment and they form the external genital organs or external genitalia.In female the gonapophyses belong to 8th and 9th segments and they form an ovipositor.In the 10th segment just below the tergum is anus supported by four podical plates which are the vestiges of the 11th segment and cerci are actually appendages of this eleventh segment.

The membrane between 5th and 6th abdominal terga forms deep pockets in the male,each pocket has two slit like pouches which are glandular and produce secretion which excites the female for copulation in the breeding season.These are called stink glands.The male genital aperture is situated between 9th and 10th sterna,while the female genital aperture is situated on the 8th sternum.

Spiracles. There are 10 pairs of spiracles ,two on the thrax and eight on the abdomen.The abdominal spiracles are smaller than thoracic ones,These are exits of respiratory system.

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Locomotion.

Cockroach is a swift runner as well as a flier.

The six legs are helpful in walking or running, when the cockroach ithird as at rest,the coxae of the legs lie back against the body and the first legs are directed forward,the hind legs are stretched out posteriorly and the middle legs take whatever position is convenient. During locomotion the first pair of leg is directed forward, they determine the course of the insect during walking or running. In locomotion on land the six legs are used as two tripods .The first and third legs one side and middle leg of the other side form a triangle on which the insect rests,while the three other legs are advanced and placed on the substratum. Then the first leg pulls and the third leg pushes ,the middle leg of the opposite side acts as pivot. The process is repeated by the other three legs and the insect moves in zig-zag fashion.

The wings are used during flight. The fore-wings are are held at right angles to the body axis and they do not beat. In fact, the beating of hind-wings with the help of flight muscles helps the cockroach in flying. The wings beat upward and downward alternately. The wings beat obliquely at every downward beat,the wings push the air downwards and backwards. Due to this, its body is propelled upwards and forwards.Thus by repeating this process in succession the cockroach flies.

Integument or Body wall.

The body wall in insects consists of three layers:

The insect integument consists of 3 basic layers;

1. Cuticle-non cellular. 2. Epidermis-cellular layer 3. Basement membrane-non cellular

1. Cuticle.

The cuticle is extremely important part of the insect body. It serves a number of important functions.

Among these are

1 It acts as a exoskeleton.

2. It prevents the loss of water from the body.

3. It reduces the rate of desiccation

4. It protects the delicate and internal parts of the body.

5. It acts as an anchor for the attachment of muscles.

6. It protects against the mechanical damage to underlying tissue.

7. It gives protection against the invasion of foreign substances.

8. It makes the lining of trachea, fore gut and hind gut.

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2. Epidermis

Epidermis is typically one cell thick. It secretes most of the cuticle. During moulting it secretes moulting

fluid which dissolves the old endocuticle before the insect moults.It absorbs the digestive products of

old cuticle and repairs the wounds.

3. Basement membrane The basement generally is 0.5 µm in thickness, is a continuous amorphous granular layer.

It is secreted by haemocytes. Muscles are attached to the basement membrane.

Sensory organs, tracheoles and nerves run through it.

Diagram of Body wall structure.

Cuticle

The cuticle is a complex non-cellular, outermost layer secreted by epidermis and is the seat of several

metabolic activities. It covers the entire surface of the body .It consists of two main layers .The outer

epicutcle and inner larger layer procuticle.Pro cuticle is further divided into two layers exocuticle (hard)

and endocuticle (soft).

The epicuticle varies in thickness from 0.03 -4.0 µm and is however a complex and important layer of

cuticle.It is a four layered structure

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A. Epicuticle.

1. Outer cement layer. It contains shellac like materials.It serves as a protective barrier for more vulnerable inner layers.

2. Waxy Layer. It consists of monolayer of lipid directly associated with cuticulin and is responsible of the permeability characteristics of the cuticle.

3. Cuticulin layer. Cuticulin is 100 Å thick and is secreted by epidermis during the formation of cuticle as small plaques. It is important in the permeability process and determines the surface appearance, soft or hard.

4. Inner epicuticle or protein epicuticle.It is the innermost layer and is composed of quinine tanned amorphous protein. It limits the expansion of cuticle during moulting.

B. Procuticle.

It is beneath the epicuticle and is about 200 µm thick.It is divided into two layers exocuticle and

endocuticle.

1. Exocuticle. The exocuticle is thin in soft bodied and thick in hard bodied insects.is highly stabilised pigmented layer and is composed of dense matrix hardened through sclerotisation.It is this part which is shed during moulting.

2. Endocuticle. The endocuticle is composed of successive light (deposited during thenight) and dark (deposited during the day) which correspond to daily growth layers. There are pore canals which are tiny tubes of 1 µm diameter twisted vertically extend from the epidermal layer to the external surface of epicuticle.

Chemical composition of cuticle.

The two major components of cuticle are chitin and various structural proteins.Chitin is colourless

polysaccharide.It is absent in epicuticle ,less in exocuticle and more in endocuticle

It is insoluble in water,dilute acid, alkalis and organic solvents but dissolves in concentrated mineral

acids.The important proteins which are present in cuticle are as follows.

1. Arthropodins-soluble proteins present in upper layers of procuticle. 2. Resilins- a rubber like protein, present in movable joints and thorax of flying insects. 3. Sclerotins-stabilised protein responsible for hard horny characters of the cuticle

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Physical properties of the cuticle.

Insect cuticle is rigid, elastic, flexible structure.The insect color is due to various pigments present in the

cuticle.Coloration is produced by complex mixture of pigments such as melanins,caretonoides,pterins

etc.Insects being essentially terrestrial are continuously faced with the problem of losing water,

especially in extreme arid habitats.Epicuticle plays a vital role in integumental permeability. If a portion

of epicuticle is dissolved by means of organic solvents,insecticides etc, increases the rate of transpiration

resulting in death.

Moulting.

There are advantages of by external skeleton however there is one serious disadvantage. The harder

parts of exoskeleton have negligible ability to stretch so that as an insect grows it must shed its skin and

grow a new one in a larger size, a process known as moulting or ecdysis.

This feature is common to all animals with external skeleton i.e., all arthropods, not only insects.

The insects replaces the cuticle a number of times,it is acomplex process involving first separation of the

old cuticle from the hypodermis(apolysis) followed by shedding of the old cuticle (ecdysis).immediately

after ecdysis, tanning of cuticle or sclerotization takes place.

Cuticular Modifications.

A seta and its socket.

1. Clothing hairs that cover the entire body and appendages as found in honey-bees. 2. Glandular setae occurring around the opening of various epidermal glands and can be seen in

lepidopteran larvae. 3. Sensory hairs are those constituting various mechano and chemoreceptors and are occurring on

the antennae, mouth parts, legs and various regions of body in all groups of insects. 4. The wing scales are modified and varyingly pigmented micro plate like structures that invade the

butterflies and moths. 5. Spines can be seen as the cuticular processes in some insects e.g., the aquatic dragonfly

larvae.Some adult beetles are possessing the cuticular horn on the apical region of the head.

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Internal Anatomy of Insects.

The main body systems that exist in the vertebrates also occur in the insects.However the nature of

these systems in the insects is different from higher animals.The main body systems that occur in insects

are .

a. Skeletal system b. Digestive system c. Circulatory system d. Excretory system e. Respiratory system f. Nervous system g. Reproductive system.

(a) Skeletal system.

As the outer body castings of insects(exoskeleton) fulfils the main function of skeleton which provides

the support and protection of soft body parts there is little internal skeleton development. Provisions

are however made for the attachment of muscles and this is achieved by the protrusions of exoskeleton

in thorax to anchor the large muscle which operate the wings and the legs.There is some development

of an internal skeleton in the head which provides extra strength and rigidity to the head capsule.and to

provide attachment to the muscles that operate the jaws of biting insects.

(b) Digestive system.

The alimentary canal of insects consists of a relatively straight tube running from the mouth in the head

to the anus at the tip of the abdomen. The digestive system performs the function of ingestion,

digestion, assimilation and ejection of unused resdues.There may be some side branches and slight

convolutions but there are no coiled portions as in higher animals. The total length of the gut is not

much more than the length of the insect itself. Three regions of the gut are recognised –foregut, midgut

and hindgut.

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Foregut or Stomodeum:

The buccal cavity is the oral part of foregut where food is taken in and pharynx follows it and leads to

crop for temporary storage of food, gizzard which is behind the crop is well developed in orders

Orthoptera and Coleoptera it has internal cuticular teeth like projections, which grinds the food. Gizzard

regulates the passage of food from crop to midgut with the help of a muscular sphincter.

Midgut or Stomach:

This is a fairly straight tubular sac. From it front part, in most insects, several finger like out growth the

gastric caeca arise. These provide additional surface area for the digestion and absorption of food.

Insects produce no mucus to lubricate the passage of food along the gut.To protect the delicate midgut

inner surface, a special membrane called as peritrophic membrane is continuously secreted by a ring

shaped gland which is located at the beginning of midgut region.

This membrane separates the food from epithelial cells. This membrane is permeable to digestive

enzymes and digestive products. This is present in all insects except liquid feeding.

About 1-100 fine tubes connect with the hind part of midgut these are the Malpighian tubules which are

excretory in function.

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Hindgut or Proctodaeum:

The hindgut usually shows two distinct regions a tubular intestinal part and a thick muscular rectum

behind opening in the anus.

Salivary Glands.

The salivary glands are paired glands which secrete saliva into preoral food cavity where it mixes with

food. Their ducts unite to form a common duct opening at the base of hypopharynx.In the larvae of

some Lepidopterous insects these are modified into

silk producing organs.Amalyse and invertase are the common enzymes found in saliva of insects,

however saliva also contains lipase and protease.

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Physiology of Digestion.

In fluid feeders, digestion may begin before the food is ingested through the injection or regurgitation of

of enzymes on the food, or in the foregut but in general digestion takes occurs in the midgut where

most of the enzymes are produced.In insects having biting and chewing type of mouthparts,food is

masticated not only in the buccal cavity but also in the proventriculus.This not only facilitates passage

through the alimentary canal but increases the surface area for enzymatic action.digestion takes place

by a series of enzymatically catalyzed steps, each producing a simpler substance until molecules of

absorbable size or nature are produced.For example, polysaccharides are broken down into small

chains, disaccharides, and finally into simple, absorbable monosaccharides (e.g., glucose): proteins are

broken down into peptones, small polypeptides, dipeptides, and finally into amino acids, which are

absorbable.

There is some correlation between the kinds of food material eaten by and kinds of enzymes present in

a given insect.Thus, cockroach which is omnivorous secretes more enzymes than tsetse fly, that feeds

primarily on blood.In addition different enzymes may be secreted by different parts of the midgut

epithelium.

(c) Respiratory System.

The Tracheal system

The respiratory system or tracheal system is involved in gaseous exchange in the insects with the

environment. In this system there is a system of internal tubes, the tracheae that directly transport the

oxygen to the parts of the body. Therefore it does not use the circulatory system as the vehicle for

gaseous exchange. The trachea open outside through segmental pores called spiracles having a system

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of closing and opening. The spiracles are morphologically, the mouths of ectodermal invaginations

which lead into a network of air tubes the trachea which are lined with thin layer of cuticle .There are

usually several large longitudinal tracheal trunks with cross connections in each body segment. From

these main trunks branches arise which divide and subdivide more finely to feed all parts of the body

very finest branches, the tracheoles are microscopic and are filled with fluid rather than air. It is here

that gaseous exchange with tissues takes place. Respiration for most insects is a passive process of

diffusion but passage of air through the trachea may in some cases be assisted by regular movement of

the body, as for example the telescopic movement of the abdomen as shown by honeybees. They are

normally placed on the pleura of thoracic and abdominal segments. Generally 10 pairs of spiracles are

seen (two pairs in thorax and eight pairs in abdomen).Sometimes the spiracles are closed and wanting

.Respiration in such cases are cutaneous.

A typical functional spiracle includes;

1. The external opening or spiracular opening.

2. The annular scelerite or peritreme surrounding the opening.

3. The atrium-the chamber in which the external opening leads.

4. The closing apparatus.

The basic tracheal system and a spiracle is shown in the figure.

Aquatic Respiratory Organs.

The aquatic insects posses closed respiratory system in which spiracles are closed and gills and hairs

assist the system in obtaining oxygen from surrounding water media.

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(d) Excretory System

The organs of excretion in insects ,which functionally resemble the kidneys in vertebrates, are the

malpighian tubules which are attached to the digestive system at the junction of midgut and hindgut

and open into the ileum at its juncture with stomach.The closed ends of malpighian tubules generally lie

free in the body cavity and they may undergo writhing movements due to the presence of muscle

strands.malpighian tubules filter out water and solvents from the insect blood or haermolymph.The

soluble nitrogenous wastes are converted into insoluble uric acid or urine which is discharged into the

lumen of the tubule. From the lumen of the tubule the urea, uric acid, ammonia .The tubules come in

contact with with blood and withdraw water ,dissolved salts and nitrogenous wastes. These materials

pass down the lumen of the tubules into the hindgut and expelled along the faeces through the anus.

Besides the Malpighian tubules there are other excretory organs such as integument,tracheal system

and alimentary canal.

(e) Circulatory System

The insects have an open circulatory system as the blood bathes the internal organs in the body cavity

called as haemocoel. The mechanism of food distribution in insects is done by blood. The blood of

insects is called haemolymph, it consists of nucleated cells or haemocytes suspended in a fluid plasma. it

does not contain haemoglobin as it does not perform transportation of gases.

The functions of blood are as follows

1. Absorption of digested food material from digestive system and removal of waste products from the tissues to the excretory organs.

2. To protect the body by ingesting foreign matter and bacteria etc.with the help of phagocytes. 3. To help in respiration. 4. To maintain balance of water.

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Circulatory organs.

The Dorsal vessel

It lies beneath the dorsal body wall and extends from posterior end of abdomen through thorax and

terminates in the head. It is continuous tubes usually closed posteriorly and always open at its cephalic

extremity. It is divisible into two regions viz. the heart or pumping organ and the aorta or a conducting

vessel.

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The Heart.

The heart lies in the abdominal region and is marked by distinct symmetrical swellings of the tube. These

dilations are known as chambers of the heart. Typically each chamber has a pair of vertical or oblique

slits the ostia in its lateral walls, one ostium on each side, placed generally behind the middle of the

chamber and sometimes close to the posterior end.

The ostia have got valves which admit the blood into the heart .There are no internal valves between

the heart chambers. The chambered part is usually restricted to the abdominal region and the number

of chambers coincide with the number of abdominal segments,the maximum being nine.

The Aorta.

It is slender anterior part of the dorsal blood vessel which extends through thorax into the head where it

opens into the viscinity of brain.It functions mainly as the main artery of the blood.

The Blood Circulation.

The heart pulsates in the forward direction. The blood in the dorsal sinus is drawn into the heart via

ostia with the expansion of heart chambers and when the systolic waves run forward, it is expelled into

the head from anterior end of the aorta.Here it percolates anteriorly, laterally and posteriorly. In the

thorax the blood collects in the ventral sinus, from where it is circulated to the legs. From the thorax a

large part of blood is drawn into the ventral sinus.Leaving the ventral sinus by the opening along the

sides and posterior end of the ventral diaphragm, the blood goes upward through preivisceral and is

drawn into the dorsal sinus.Here it enters the dorsal vessel through the ostia and is again driven forward

into the head.The two rhythms of blood circulation are called Diastole ( blood entering the heart during

expansion) and Systole ( contraction - expelling the blood).The rate of heart beat is variable in insects in

cockroach it is 49/minute.The increase in temperature increases pulse rate. The pulse rate falls to

minimum during diapause.

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(f) Nervous System

The nervous system of insects is highly developed and serves as a connecting link between sense organs

(which respond to various stimuli) and affecter organs i.e., muscles and glands. Hence the nervous

system perceives and transmits stimuli or impulses from one part of the body to another.

It is made up of neurons or nerve cells. Neurons are made up of specialised ectodermal cells. These

neurons consist of a cell body with a nucleus,a long filament or axon with lateral branches and one or

more branch processes, the dendrons or dendrites arising from the cell. The dendrites transmit impulses

towards the central cell body and axon transmits them away from it.A group of neurons is known as the

ganglia. Depending upon the number of axons, the neurons may be called as unipolar with one axon,

bipolar with two axons, multipolar with many axons.

Kinds of neurons.: Based on the functions neurons are grouped into three kinds.

1. Sensory neuron or afferent neuron: associated with sensory organs and lie near integument (Bipolar).Convey impulse from the sense organs and it ends with terminal arborizations in central ganglia.

2. Motor neurons or efferent neurons: Always lie within the ganglia (unipolar).Their nerves pass to the muscles and convey impulses outwards to the effector organs.

3. Associated neurons: The axon and collateral of an association neuron make a two way connection between neurons of sensory and motor systems.

Ganglion:

An aggregation of neurons.The ganglia also contain collaterals of motor nerves and terminal

arborisation of sensory axon. The ganglion cells are mostly situated on the periphery of ganglion.

The central part of the ganglion is occupied by nerve fibrils which constitute the neuropile.

The Nervous system of an insect can be divided into

a. The central nervous system b. The visceral or sympathetic nervous system c. The peripheral nervous system.

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a. The central nervous system

The main nerve cord is located in the ventral body region beneath the gut and the brain is situated in

the head above the digestive tract. It comprises of i. The brain ii. Sub oesophageal ganglion iii. The

ventral nerve cord.

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(i) The Brain. It lies just above the oesophagus and is situated in the head. It has three paired divisions viz. the protocerebrum (fore brain) the deutrocerebrum (mid brain) and the tritocerebrum

(hind brain). The protocerebrum innervates the compound eyes and ocelli.The deutrocerebrum

innervates the antennae. The tritocerebrum controls the major sympathetic nervous system.

(ii). Sub oesophageal ganglion: It is the ventral ganglionic centre of the head. It is formed by

the fusion of the ganglion of the maxillary,mandibular and labial segments and gives

off paired nerves supplying their respective appendages. A pair of connectives pass

through the neck into thorax from this nerve centre.

(iii). The ventral nerve cord. It consists of a series of ganglia lying in each segment on the floor of the

thorax and abdomen. The ganglia of the adjoining segments are united into a longitudinal chain by a pair

of connectives which issue from the posterior border of the sub oesophageal ganglion. This chain is

known as ventral nerve cord.

The first three are located in the thoracic segment and are called as thoracic ganglia.The remaining five

in the abdominal ganglia are called as abdominal ganglia, innervate the muscles and the reproductive

organs.

b. The visceral or sympathetic nervous system Insects posses a so called visceral or sympathetic nervous system that controls some of the involuntary

motions of the anterior portion of the gut and dorsal blood vessel.It is made up of three separate sub

systems

(i). Stomogastric nervous system consists of small ganglia and associated nerves. It includes frontal

ganglion, which is on dorsal midline of oesophagus and it connects with tritocerebrum by nerves on

either side. The recurrent nerve arises medially from frontal ganglion and extends beneath and posterior

to the brain.The recurrent nerve ends posteriorly in a hypocerebral ganglion, which give rise to one or

two gastric nerves, or ventricular nerves which continue posteriorly and terminate with a ventricular

ganglion.

Two endocrine glands corpora cardiaca and corpora allata are connected are connected with nerves to

the hypocerebral ganglion.The suboesophageal gland is also connected with the hypocerebral ganglion

by a nerve.

The stomatogastric system regulates the the swallowing movements and labral muscles,mandibular

muscles and the salivary glands.

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(ii). Ventral visceral nervous system. is associated with the ventral nerve cord and its ganglia.

From each segmental ganglion a single median nerve arises and divides into two lateral nerves.

These nerves innervate the muscles and regulate the closing and opening of segmental spiracles.

(iii). Caudal visceral nervous system. is associated with posterior segments of the abdomen. The nerves

of this system arise from the caudal ganglion of the ventral chain and supply the posterior portions of

the hindgut and the internal reproductive organs

c. The peripheral nervous system.

The fine nerves of the peripheral nervous system are branches of all the nerves radiating from the

ganglia of central and sympathetic nervous systems. There are many bipolar and multipolar

nerve cells beneath the hypodermal layer of the body wall. The prolongations of these nerve cells form a

network of nerves which form peripheral nervous system. The peripheral nervous system innervates

the sense hairs and continuously informs the insect about its surroundings by receiving stimuli through

sense hairs of the body wall.

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peripheral nervous system

sense organs in the integument

chemoreceptors and tactile hairs

↓

sensory fibres

central nervous system

interneurons

brain,nerve cord & ganglia

Motor fibres

neurohormones

Muscles,wings,legs

and other mobile

structures

Haemolymph to control

movement of

heart,gut,malpighian

tubules and other

functions

sensory fibres

neurohormones

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visceral nervous system

stomogastric Ventral

sympathetic

Caudal

sympathetic

↓ ↓ ↓

Foregut and spiracles and reproductive organs

salivary glands heart and anal appendages

A model of major relationship of insect nervous system.

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(g) Reproductive system

It is an essential physiological process for the propagation of insect species. The reproductive system in insects

consists of internal and external organs. Gonads gonadal ducts and accessory are the internal reproductive

organs and the genetalia that serves copulation and ovipositor are the external organs. Insects are usually

bisexual.

Male Reproductive System consists of

a. Paired testes composed of follicles. b. A pair of vasa deferentia. c. The seminal vesicle. d. Ejaculatory duct e. Accessory glands. f. Penis or aedeagus

a. A pair of testes. Each testis consists of number of small tubules or follicles which are cylindrical in shape.These tubules contain

sex cells in different stages of development.The number of these tubules vary in different insects.

b. A pair of vasa deferentia. The vasa deferentia of two sides lie on the ventral aspect of the testicular mass.Each vas deferens turns

around the alimentary canal and joins the fellow of the other side in the 9th abdominal segments.

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c. The seminal vesicle. Each vasa deferensbefore meeting to each other takes the form of a vesicles known as seminal vesicles.These

form the storage place for the mature sperms.

d. Ejaculatory duct. The common duct formed by the union of vasa deferentia is known as ejaculatory duct.

e. . Accessory glands There are 3 pairs of accessory glands arising from the anterior end of the ejaculatory duct.They secrete a

substance which hardens the spermatozoa to form a capsule known as spermatophore

f. Penis or aedeagus The terminal section of the ejaculatory duct is enclosed in in a finger like evagination of the ventral body wall

which forms the aedigus or penis .It lies on the floor of the 9th abdominal sternum of the grasshopper.

Female Reproductive System consists of

a. A pair of ovaries. b. A pair of oviducts c. Spermatheca d. A pair of accessory glands or collateral glands. e. A copulatory pouch (genital chamber or vagina)

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The Ovaries. They lie in the body cavity of the abdomen on either side of the alimentary canal.

The ovaries are in form of a number of tapering tubules known as ovarioles which open laterally into the

oviducts. The number of ovarioles in ovary varies greatly in different insects, usually

4-8 but in some Hymenoptera and Diptera it is 100-200. In Isoptera it could be 2400 or more.

Each ovariole contains number of eggs in different stages of development. Fully developed eggs lie near

the base and least developed are near the apex. Three zones are recognisable in the ovariole viz (a). the

terminal filament this is thread like apical peritoneum. The filaments of the ovarioles of one ovary

combine to form a common thread which unites with that from the ovary of opposite side to form a

median or terminal ligament. There is a region called as germarium at the apex below the terminal

filament.It consists a mass of cells from which are differentiated the the primordial germ cells.Next to

this is a region called as vitllarium is the region of growth this contains developing eggs and nutritive

cells (nurse cells).

Oviduct. The lateral oviducts are pairedcanals leading from ovaries. The two oviducts join to form a

common oviduct and opens posteriorly into female gonopore which is in the genital chamber or the

vagina.

Spermatheca.It is a pouch or sac for the storage of sperms as in insects insemination of the egg is not

generally accomplished during the act of mating but takes place at a varying length of time later, most

females are provided with this pouch for storage of spermatozoa and ejected upon the eggs when the

eggs are extruded from the oviduct.

Accessory glands. They open into vagina and secrete an adhesive substance for connecting the eggs

each other and to the substratum..In cockroaches the secretion forms ootheca or egg capsule.

Genital chamber or Vagina. The common oviduct opens posteriorly into genital chamber or vagina.

Fertilization. The spermatic fluid of the male is stored in the spermatheca after mating when the egg

comes down from oviduct to the vagina. The egg is fertilized, the egg consists of an opening called as

micropile from where the spermatozoan enters.Only one spermatozoan can fertilize an egg.

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Types of Reproduction.

Most insects are oviparous i.e., they lay eggs which hatch after deposition.Exceptions to these

generalizations are:

a. Viviparity: species in which embryonic development is completed within the body of the female parent, which produces larvae or nymph instead of laying eggs are viviparous. They produce fewer offspring than oviparous insects.

b. Polyembryony: Here there is production of two or more embryos from a single egg. Sometimes an egg instead of giving rise to a single larva may produce two or more.

c. Parthenogenesis: Sometimes eggs develop without being fertilized e.g., aphids d. Paedogenesis: Sometimes larvae are able to reproduce and this is known as paedogenesis.

Copulation.

The active breeding season of cockroach starts from March to September. Copulation occurs at night.

During copulation, the male cockroach finds a suitable mate and the two partners come together by the

posterior ends. The male opens the gynovalvular plates of the female by its titillator and inserts its

phallometers into the genital chamber of the female.The pseudopenis of the male is inserted into the

gonopore of the female and rotated transversely to hold it in position.The anterior gynopophyses of the

ovipositor are held by the right phalomere.The ventral phallomere moves to the right opening the

gonopore of the ejaculatory duct,then,the spermatophore is expelled and deposited directly on the

spermathecal papilla to which it is fixed in about an hour.

The phallic gland now pours its secretion on the spermatophore to form its outer most covering which

hardens in about two hours.Copulation lasts for about an hour and a quarter,after which the two

cockroaches separate.The sperms pass from spermatophore into the spermathece slowly in the course

of the next 20 hours after which empty spermatophore is discarded.

Ootheca formation.

The eggs come alternately from the two ovaries into the common oviduct and pass through the female

gonophores into genital chamber where they are fertilized by the sperms coming from the

spermatecae.The two collateral glands pour their different secretions on fertilized eggs,these secretions

combine to form a scleroprotein which hardens to form a dark brown ootheca around the eggs.The

ootheca is shaped and moulded by ovipositor and the walls of the oothecalchamber.The ootheca is

12mm in length,one side it I has straight crest with serrated margin ,it contains 16 fertilised eggs

standing vertically in rows,the position of the egg can be seen on the outer surface of the ootheca.The

ootheca is completed in about a day and it protrudes from the oothecal chamber,being held in place by

by the 10thtergum and gynovalvular plates. The female cockroach carries ootheca for several days and

finally drops it in some dark,dry place.Every female cockroach produces nearly 15 to 40 ootheca in its

life span of about one to two years.

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Life History.

The eggs of cockroach, like other insects are called as centolecithal because the ooplasm is placed in the

form of a thin film outside thea central mass of yolk.The embryonic development is complete,the

ootheca is ruptures and the young ones hatch out.aThe young ones of cockroach resemble their parents

in every respect except that they are smaller in size and without wings.These are called as nymphs

which undergo metamorphosis.

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Metamorphosis in Insects.

Metamorphosis refers to the way that insects develop, grow, and change form. Metamorphosis

actually means "change". There are two types of metamorphosis--incomplete and complete.

Incomplete Metamorphosis

About 12% of all insects go through incomplete metamorphosis. Incomplete metamorphosis has

3 stages.

Egg - A female insect lays eggs. These eggs are often covered by an egg case which protects the eggs and holds them together.

Nymph - The eggs hatch into nymphs. Nymphs looks like small adults, but usually don't have wings. Insect nymphs eat the same food that the adult insect eats. Nymphs shed or molt their exoskeletons (outer casings made up of a hard substance called chitin) and replace them with larger ones several times as they grow. Most nymphs molt 4-8 times.

Adult - The insects stop molting when they reach their adult size. By this time, they have also grown wings.

Complete Metamorphosis

Complete Metamorphosis

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About 88% of all insects go through complete metamorphosis. Complete metamorphosis has 4

stages:

Egg - A female insects lays eggs. Larva - Larvae hatch from the eggs. They do not look like adult insects. They usually have a

worm-like shape. Caterpillers, maggots, and grubs are all just the larval stages of insects. Larvae molt their skin several times and they grow slightly larger.

Pupa - Larvae make cocoons around themselves. Larvae don't eat while they're inside their cocoons. Their bodies develop into an adult shape with wings, legs, internal organs, etc. This change takes anywhere from 4 days to many months.

Adult - Inside the cocoon, the larvae change into adults. After a period of time, the adult breaks out of the cocoon.

No Metamorphosis. In the case of insects with no apparent metamorphosis (ametabolous insects), adults differ from nymphs only in size and in possession of fully developed reproductive organs. Included in this group are springtails and silverfish.

Gradual Metamorphosis. Insects with gradual metamorphosis (paurometabolous insects),

include many orders with some of pests. Nymphs and adults live in the same habitat and feed on the same foods. Inmature forms are known as nymphs. Included in this group are grasshoppers, crickets, cockroaches, termites, booklice and aphids.

Gradual Metamorphosis.