Topics to be Learn : 

  • Introduction
  • Habit and Habitat
  • Systematic Position
  • External Morphology
  • Body Cavity
  • Digestive System of Cockroach
  • Circulatory System or Blood Vascular System
  • Respiratory System or Tracheal System
  • Excretory System
  • Nervous System
  • Reproductive System
  • Interactions with Mankind
Types of Animals
  • Unicellular and multicellular
  • Prokaryotic and eukaryotic
  • Vertebrates and invertebrates
  • Unisexual and hermaphrodite
  • Aquatic, terrestrial, amphibian, reptilian, aerial, etc.
Habit and Habitat
  • Cockroaches are found worldwide, earning the title "omnivorous" (present everywhere).
  • Prefer damp, moist areas and crevices.
  • Active at night, making them nocturnal.
  • Cursorial insects: adapted for running on land.
  • Common cockroach species in India: Periplaneta americana, Blattella orientalis & Blattella germanica.
  • Cannibalism: Cockroaches may eat their young.
Systematic Position

 

External Morphology of Cockroach

Shape & Size:

  • Elongated, bilaterally symmetrical, dorso-ventrally flattened.
  • Triploblastic, eucoelomate.
  • Haemocoel (body cavity) filled with haemolymph (fluid).

Coloration:

  • Glistening brown or reddish-brown.

Exoskeleton:

  • Tough, waxy, non-living chitinous exoskeleton.
  • Made of chitin, a nitrogenous polysaccharide providing strength, elasticity, and surface area for muscle attachment.
  • Each segment covered by 4 chitinous plates called sclerites: Dorsal tergum, Ventral sternum & Lateral pleurons (two)

Body Division: Divided into three regions: Head, Thorax & Abdomen

Head:

  • Formed by the fusion of 6 segments.
  • Triangular or ovate shape.
  • Highly mobile due to a flexible neck.
  • Contains: Long antennae, Compound eyes, Mouthparts adapted for biting and chewing food.
Cockroach Head

Structures on the Head

1. Antennae (Feelers)

  • Long, filamentous, and segmented.
  • Located in membranous pits (antenna sockets).
  • Can move in all directions.
  • Tactile (touch) and olfactory (smell) organs.
  • Function: Help in locating food material in the surroundings.

2. Fenestrae (Ocellar Spots)

  • Small, white spots located at the base of each antenna.
  • Known as ocellar spots.

3. Compound Eyes

  • Paired, dark, kidney-shaped structures on the dorsolateral sides of the head.
  • Made of around 2000 hexagonal ommatidia (structural units of the eye).
  • Each ommatidium forms an image of a small portion of the visual field.
  • Mosaic vision: produces a combined image from many ommatidia.
  • Provides low resolution but high sensitivity to motion.

4. Mouthparts

  • Pre-oral cavity: Food is received here before being processed.
  • Chewing and biting type mouthparts:
    • Labrum (upper lip)
    • Labium (lower lip)
    • Mandibles (pair of jaws)
    • Maxillae (pair of jaw-like structures)
    • Hypopharynx: Tongue-like structure in the center of the mouth.
  • Salivary duct opens at the base of the hypopharynx.
  • The mouth opens into the foregut.

Thorax

Segments:

  • Prothorax (anterior segment)
  • Mesothorax
  • Metathorax (posterior segment)

Legs:

  • Three pairs of walking legs (one pair per segment).
  • Each leg has five podomeres: Coxa, Trochanter, Femur, Tibia, Tarsus (final segment, made of 5 movable tarsomeres).
  • Tarsus ends with: A pair of claws, Arolium (cushion-like structure) to help cling.

Wings:

  • Forewings: First pair, dark, opaque, leathery wings. Protective function.
  • Hindwings: Second pair, thin, membranous, used for flight.
  • Attachment: Forewings and hindwings are attached to the mesothorax and metathorax.
Abdomen

Segments: Elongated, made up of 10 segments.

  • Each segment has a dorsal tergum and ventral sternum.
  • Tergum is joined to sternum by a soft cuticle called pleura.
  • Posterior segments are telescoped, overlapping 8th and 9th tergum.
  • 10th tergum projects backward and is deeply notched.
  • Bears anal cerci (pair of small, jointed appendages).

Gender Differences:

  • Males: Narrow and tapering abdomen, with a short, unjointed anal style on the 9th sternum.
  • Females: Wider abdomen compared to males.

Spiracles:

  • 10 pairs of spiracles: 2 on the thorax, 8 on the abdomen
  • Spiracles allow air to enter and exit the trachea (respiratory system).
Know This
  • Moulting: Process of forming a new chitinous exoskeleton and shedding the old one. This allows growth in insects.
  • Simple Eyes: Contain one lens and sensory cells. Detect movement, but don’t form complex images.
  • Fenestrae (Ocellar Spots): Undeveloped simple eyes that are sensitive to light but cannot form images.
  • Complex Eyes: Contain multiple ommatidia (each with its own lens). These form a complex image and detect movement.
Body Cavity
  • The haemocoel (body cavity) surrounds the viscera (internal organs).
  • Filled with blood due to open circulation.
  • Contains fat bodies: Appear as a whitish mass of tissue. Made of polygonal cells containing fat, proteins, and occasionally glycogen.

Digestive System of Cockroach

Mouthparts

1. Pre-oral Cavity: Area in front of the mouth where food is received. Bound by chewing and biting mouthparts.

2. Labrum (Upper Lip):

  • Function: Holds food during feeding.

3. Mandibles (Jaws):

  • Structure: Hard, dark, chitinous, serrated jaws on either side of the mouth.
  • Function: Cut and crush food through coordinated side-to-side movements.

4. Maxillae (Accessory Jaws):

  • Structure: Paired, behind mandibles, with parts like cardo, stipes, galea, lacinia, and maxillary palps.
  • Function: Hold food, assist mandibles in chewing, clean antennae and front legs. Maxillary palps act as tactile organs.

5. Labium (Lower Lip):

  • Structure: Covers the pre-oral cavity from below. Attached to the posterior part of the head. Contains three jointed labial palps (sensory).
  • Function: Pushes chewed food into the pre-oral cavity and prevents food loss during chewing.

6. Hypopharynx (Tongue):

  • Structure: Cylindrical structure between the first maxillae.
  • Function: Helps mix saliva with food during feeding. Contains salivary duct.
Alimentary Canal
  • Length: 6–7 cm long, with two openings (mouth and anus).
  • Divisions: The alimentary canal is divided into three parts: Foregut, Midgut, and Hindgut.
(i) Foregut (Stomodaeum)
  • Pharynx: Short, narrow, muscular tube, contains taste sensillae. Function: Moves food into the oesophagus.
  • Oesophagus: Slightly long, narrow tube connecting pharynx to crop.
  • Crop: Large, sac-like organ. Function: Temporarily stores food before it moves to the gizzard.
  • Gizzard (Proventriculus): Small, spherical organ with six chitinous teeth and bristles. Function: Crushes food with teeth and filters food with bristles.
(ii) Midgut (Mesenteron)
  • Ventriculus (Stomach): Short, narrow tube lined with glandular epithelium. Function: Digestion and absorption of nutrients.
  • Hepatic Caeca: Thin, transparent, hollow tubules. Function: Secrete digestive enzymes.
(iii) Hindgut (Proctodaeum)
  • Ileum: Short, narrow part of hindgut. Function: Directs nitrogenous wastes and undigested food to the colon.
  • Colon: Long, wide part of hindgut. Function: Reabsorbs water from waste and directs material to the rectum.
  • Rectum: Oval or spindle-shaped terminal part. Function: Absorbs water from waste using rectal pads and stores undigested food.
  • Anus: Located at the ventral side of the 10th segment. It is the opening where undigested food is expelled.
Salivary Glands

Pair of Salivary Glands: Secrete saliva to aid in digestion.

  • Structure: Each gland has two lobes and a receptacle (reservoir).
  • Function: Secretion of saliva; saliva is transported through ducts.
  • Salivary Ducts: Both ducts unite to form a common efferent salivary duct, which opens at the base of the hypopharynx (tongue).
Circulatory System of Cockroach

Type: Open circulatory system.

Blood: The blood in cockroaches is colourless (haemolymph), containing plasma and seven types of blood cells/haemocytes. Plasma is rich in nutrients and nitrogenous wastes like uric acid.

Haemocoel: The body cavity, known as haemocoel, is divided into three sinuses by two diaphragms.

  • Dorsal diaphragm: Contains 12 pairs of alary muscles (fan-like muscles), which help in blood circulation. These muscles are attached to the terga (dorsal side) and extend between the heart and diaphragm.
  • Ventral diaphragm: A flat diaphragm located above the ventral nerve cord.
Sinuses: The coelom (body cavity) is divided into three sinuses:
  • Pericardial sinus: Small, contains the dorsal vessel.
  • Perivisceral sinus: Largest, contains fat bodies and major organs like the alimentary canal and reproductive system.
  • Perineural sinus: Small, contains the ventral nerve cord and extends to the legs. The sinuses communicate via pores between the diaphragms.
Dorsal Blood Vessel
  • Structure: The dorsal blood vessel is located in the pericardial sinus, just beneath the tergum.
  • Heart: A narrow, muscular, 13-chambered tube, open anteriorly and closed posteriorly.
  • Location: Starts from the 9th abdominal segment and extends to the 1st thoracic segment.
  • Chambers: The heart has 13 chambers; 10 in the abdominal region and 3 in the thoracic region. Each chamber has a pair of ostia (vertical incurrent apertures) that allow blood to flow from the sinuses into the heart.
  • Anterior Aorta: A short, thin-walled vessel continuing from the heart that opens into the haemocoel in the head region.
Mechanism of Blood Circulation

1. Heart Contraction (Systole):

  • Starts at the posterior end, with the contraction wave passing anteriorly, pushing blood towards the dorsal aorta.
  • During systole, ostia close, preventing backflow.
  • Blood is pushed into the head region and then into the perineural sinus and perivisceral sinus.

2. Heart Relaxation (Diastole):

  • During diastole, the heart expands.
  • Alary muscles contract, making the dorsal diaphragm flat.
  • Blood flows from the perivisceral sinus to the pericardial sinus through the fenestrae and into the heart through the ostia.

3. Diastasis: The heart remains expanded and blood flow is maintained.

4. Systolic Contraction of Alary Muscles: The dorsal diaphragm becomes convex, reducing the volume of the pericardial sinus, pushing blood into the perivisceral sinus.

Key Points
  • Open Circulatory System: Blood is not confined to vessels; instead, it flows freely in the haemocoel and directly bathes tissues.
  • Poorly Developed Blood Vessels: Blood vessels are not well-developed and are open into the body cavity.
  • Heart Structure: The heart lies along the mid-dorsal line of the thorax and abdomen and has 13 chambers.
  • Blood Flow: The blood is pumped anteriorly from the heart to the sinuses, which directly bathe the organs.
Cockroach: Respiratory, Excretory, and Nervous System Notes

Respiratory System or Tracheal System

Tracheal System: A network of air tubes that bring air directly into the body, allowing gas exchange between air and tissues without using blood.

Spiracles:

  • Paired respiratory openings located on the ventro-lateral side of the body.
  • Found on the thoracic and eight abdominal segments.
  • Open into air sacs, from which tracheal tubes arise.

Trachea:

  • Branching tubes that are about 1mm thick.
  • Have spiral or annular thickening of chitin to prevent collapse.
  • Branch further into tracheoles.

Tracheoles:

  • Fine intracellular tubes that penetrate deeply into tissues.
  • They are not lined with chitin.
  • End blindly in cells, filled with a watery fluid for gas exchange.
  • During high activity, fluid is drawn into tissues for more oxygen intake.

Air Renewal:

  • Rhythmic movements of thoracic and abdominal muscles help renew air in the tracheal system.
  • Sphincters control the opening of spiracles.
Excretory System

Malpighian Tubules:

  • Main excretory organs, 150 in number.
  • Thin, yellow-colored, ectodermal structures in the haemocoel.
  • Attached to the midgut and hindgut.

Malpighian Tubules Structure:

  • Lined with a single layer of glandular epithelial cells.
  • The distal portion is secretory, while the proximal part is absorptive.

Excretion Process:

  • Extracts water and nitrogenous wastes from the haemocoel.
  • Converts them into uric acid and passes it to the ileum.
  • Uricotelic: Cockroaches excrete uric acid.

Additional Excretory Structures:

  • Fat bodies, nephrocytes (urate cells), and uricose glands (in males) help in excretion.
  • Nephrocytes store nitrogenous wastes along with fat bodies or near the heart.
  • Excretory products are removed in the haemocoel, with some waste eliminated during moulting.
Nervous System

Ventral, Solid, and Ganglionated: The nervous system consists of:

  1. Central Nervous System (CNS)
  2. Peripheral Nervous System (PNS)
  3. Autonomous Nervous System (ANS)

Nervous System Distribution:

  • Spread throughout the body.
  • The head contains part of the nervous system, while the rest runs along the ventral part of the body.

Central Nervous System (CNS)

1. Nerve Ring: Composed of:

Supra-oesophageal Ganglia:

  • Also known as the brain.
  • Located above the oesophagus and between the antennae.
  • Formed by the fusion of three small ganglia: Protocerebrum, Deutocerebrum & Tritocerebrum

Circum-oesophageal Connectives:

  • Pair of lateral nerves connecting the supra-oesophageal ganglia to the sub-oesophageal ganglia.

Sub-oesophageal Ganglia:

  • Bilobed, located below the oesophagus in the head.
  • Formed by the fusion of three pairs of ganglia.

2. Ventral Nerve Cord:

  • Originates from the sub-oesophageal ganglion.
  • Located along the mid-ventral position in the perineural sinus.
Double nerve cord with nine segmental paired ganglia:
  • Thoracic Ganglia: First three pairs of segmental ganglia (large).
  • Abdominal Ganglia: Last six pairs, with the 6th abdominal ganglion being the largest, located in the 7th abdominal segment.
  • No ganglion in the 6th segment.
Peripheral Nervous System (PNS)

Composed of nerves arising from CNS ganglia.

  • Supra-oesophageal Ganglia: Six pairs of nerves supply to: Eyes, Antennae & Labrum
  • Sub-oesophageal Ganglion: Nerves supply to: Mandibles, Maxillae & Labium
  • Thoracic Ganglia: Nerves supply to: Wings, Legs & Internal thoracic organs
  • Abdominal Ganglia: Nerves supply to the abdominal organs of respective segments.
Autonomic Nervous System (ANS)
  • Composed of four ganglia and a retro cerebral complex.
Ganglia:
  • Frontal Ganglion: Located above the pharynx and in front of the brain.
  • Hypocerebral Ganglion: Located on the anterior region of the oesophagus.
  • Ingluvial Ganglion: Also called visceral ganglion, located on the crop.
  • Ventricular Ganglion: Located on the gizzard.
Cockroach Reproductive System Notes

Male Reproductive System

1. Primary Sex Organs: Testes

  • Paired organs located in the 4th and 6th abdominal segments.
  • Produce sperms.

2. Vasa Deferentia:

  • Thin, tubular structures that carry sperms from the testes.
  • Open into the ejaculatory duct through seminal vesicle.

3. Ejaculatory Duct:

  • Opens into the male gonopore, located ventral to the anus.

4. Seminal Vesicles:

  • Store sperms as spermatophores (bundles of sperm).
  • Spermatophores are deposited into the female reproductive tract during copulation.

5. Accessory Gland:

  • Mushroom-shaped gland (utricular gland).
  • Located in the 6th-7th abdominal segments.

6. Male Gonapophyses (Phallomere):

  • Form the external genitalia.
  • Three asymmetrical chitinous structures surrounding the male gonophore.
Female Reproductive System

1. Primary Sex Organs: Ovaries

  • Paired ovaries located laterally in 2nd-6th abdominal segments.
  • Each ovary has eight ovarian tubules (ovarioles) containing developing eggs.

2. Ovarioles:

  • All ovarioles of one ovary open into the lateral oviduct.

3. Common Oviduct (Vagina):

  • Both lateral oviducts unite to form the common oviduct.
  • Opens into the Bursa copulatrix (female copulatory organ).
Genital Pouch (in both Male and Female)

1. Male Genital Pouch:

  • Located at the hind end of the abdomen.
  • Bounded dorsally by the 9th and 10th terga, and ventrally by the 9th sternum.
  • Contains: Dorsal anus, Ventral male genital pore & Gonapophysis

2. Female Genital Pouch:

  • Formed by the 7th, 8th, and 9th sternum.
  • Brood or genital pouch contains: Gonopore, Spermathecal pores & Collateral glands
Fertilization and Formation of Ootheca

1. Fertilization:

  • Internal fertilization.
  • Male and female come together by their posterior phallomeres.
  • Spermatophores are transferred to the female genital chamber.
  • Sperms reach the spermatheca.
  • Eggs are released from ovaries into the common oviduct and pass into the genital chamber.
  • Sperms fertilize the eggs in the genital chamber.

2. Ootheca (Egg Case):

  • Secreted by collateral glands, forms a capsule around fertilized eggs.
  • Measures about 8 mm long, ranging from dark reddish to blackish brown.
  • Contains 14-16 fertilized eggs in two rows.
  • Eggs are deposited on suitable surfaces like cracks or crevices, near humidity and food.
  • Female produces about 9 to 10 oothecae during its lifespan.
Stages of Development in Cockroach

Development Type: Paurometabolous

  • Fertilized Egg → Nymph → Adult

Nymph:

  • Looks like an adult but is smaller and sexually immature.

Instar:

  • Nymph undergoes moulting.
  • Stages between two successive moults are called instars.
  • 13 moults before reaching adult stage.

Wings:

  • Nymphs have wing pads but only adults have fully developed wings.

Embryonic Period:

  • Varies with temperature and humidity: At 24°C, duration is about 58 days & At 30°C, duration is about 32 days.
Cockroach Interactions with Mankind and Control Measures

Negative Interactions: Cockroaches as Pests

1. Damage to Household Materials:

  • Cockroaches damage clothes, shoes, paper, and food.
  • They eat and destroy food supplies.

2. Contamination of Food:

  • Cockroaches contaminate food, giving it a typical smell and making it unpalatable.

3. Health Risks:

  • Cockroaches carry harmful pathogens from sewage and gutter holes.
  • They are responsible for spreading diseases such as: Cholera, Diarrhoea, Tuberculosis, Typhoid.

4. Bio-indicators of Unhygienic Conditions:

  • Their presence indicates unhygienic and unsanitary living conditions.
Cockroaches in the Food Chain

1. Prey for Other Animals:

  • Amphibians, birds, lizards, and rodents prey on cockroaches, making them part of the food chain.

2. Human Consumption:

  • In regions like South America, China, and Myanmar, some people eat cockroaches as food.
Uses of Cockroaches

Laboratory and Biological Research:

  • Cockroaches are used as experimental animals in laboratories due to their easy availability.
  • Their use in research helps in understanding biological processes without harming the ecological balance.
Control Measures

1. Good Sanitation:

  • Regularly clean dark, humid areas like kitchens, cupboards, and trolleys.
  • Seal cracks and crevices in the home.
  • Prevent the accumulation of garbage.

2. Maintain Drain Traps:

  • Keep drain traps filled with water to prevent cockroaches from migrating from sewers into homes.

3. Chemical Control:

  • Use chemical control methods with substances like: Organophosphates, Carbamates, Pyrethroids, Boric acid.
  • These chemicals are available in different formulations under various brand names.