COCKROACH

Periplaneta americana

· Cockroaches belong to the class Insecta of the phylum Arthropoda.
· Two species of cockroaches commonly found in India are Periplaneta americana and Blatta orientalis.
· The generic name Periplaneta was given by Burmeister (1838 AD).
· Periplanela americana is the largest and the most common species.
· Cockroaches are cursorial (running) and nocturnal.
· The adult P. americana measures 28‑44 mm in length and is dark brown in colour.

MORPHOLOGY

· Body is covered with the chitinous exoskeleton of sclerites.
· Body is divided into head, thorax, and abdomen.
· Head is derived by the fusion of six embryonic segments.
· The sclerite of the head is fused to form a head capsule.
· The part of the head between and behind the eyes is epicranium (vertex).

(A) Male Cockroach (B)Female Cockroach

· The front of the head capsule is made up of three unpaired flattened sclerites called frons, clypeus, and labrum.

· Head bears a pair of long antennae, a pair of ocelli or fenestrae, and a pair of compound eyes.

· The thorax consists of three segments: the prothorax, mesothorax, and metathorax.
· Thorax bears three pairs of jointed appendages and two pairs of wings on mesothorax and metathorax.

· Abdomen is the largest and broadest part consisting of ten segments (11 segments in embryo) without appendages.

. The 11th somite of the embryo is represented in adults by podical plates.

MALE

· Exoskeleton of each segment consists of four chitinous plates called sclerites.
· The dorsal sclerite is called tergum or tergite, ventral sclerite is sternum or sternite and two lateral sclerites are called pleura or pleurites.
· The dorsal plate of the thorax is called notum.
· The antenna is made of many segments, podomeres.
· The first segment of the antenna is the scape (largest), the second pedicel, and the rest of many jointed flagella.
· Antenna is a thigmo receptor sensitive to touch.

MOUTHPARTS

Mouthparts of Cockroach

· Mouthparts of cockroaches are the mandibulate type or cutting and chewing type. Mouthparts consist of the labrum (upper lip), labium (lower lip), maxillae (segmented and resemble a leg), mandibles, and hypopharynx (tongue).
· The main structures of mastication (chewing) are mandibles which are short with teeth.
· Maxilla consists of the cardo, stipes, galea, lacinia, and 5‑segmented maxillary palp.
· Labium (second maxilla) consists of a submentum. mentum, prementum, palpiger, paraglossa, glossa, and three jointed labial palp.
· Glossa and paraglossa are collectively called lingula. A common salivary duct opens at the base of the hypopharynx.

· The study of mouthparts in insects is done under homology and adaptation.

WINGS

· Cockroach has two pairs of wings.
· The first pair (mesothoracic) is thick, hard, and leathery, protective in a function called tegmina (elytra).
· Second pair (metathoracic) is thin, soft, and membranous.
· Cockroach does not fly, it is a cursorial insect, but the wings help in escaping from danger.
· Both mesothoracic and metathoracic wings have venation.

APPENDAGES

Leg of Cockroach

· Leg of cockroach is five segmented, segments from the base are coxa, trochanter, femur, tibia, and tarsus.
· Tarsus is subdivided into five tarsomeres. The last tarsomere is called pretarsus forming the claws and bearing an adhesive arolium or pulvillus.
· Similar but smaller adhesive pads called plantula are located at each joint of the tarsus.
· The most swollen segment in the leg of the cockroach is coxa.
· The longest segment in the leg of the cockroach is the tibia.
· Abdominal segments are without lateral appendages.
· Anal cerci, a pair of many jointed structures are present on the tergite of 10th segment in both sexes.
· Each anal cercus is made of 15 segments.
· Anal styles; a pair of small, spine‑like unjointed structures are present on sternite of 9th segment in males only.
· Anal cerci bear minute sensory hairs which are sensitive to sound and other vibrations.

BODY WALL

· Body wall of the cockroach is made up of two layers, the outer cuticle, and the inner hypodermis.
· Cuticle is invaginated forming endoskeletal elements like tentorium in head and apodemes in the thorax providing sites for attachment of muscles.
· The cuticle has three distinct layers: outer primary cuticle or epicuticle, middle thick exocuticle, and inner thick endocuticle.
· Exo and endocuticle together constitute the so-called procuticle'.
· The epicuticle is formed of tanned protein; it has no chitin.
· Exo and endocuticle contain chitin, a structural poly saccharide, the basic unit being N‑acetyl glucosamine.
· Melanin pigment is found only in exocuticle.
· Hypodermis is a single-layered epithelium. Some of its cells are modified into large oval trichogen cells concerned with the secretion of movable bristles on the body of a cockroach.
· Large irregular cells called 'oenocytes secrete wax which covers the cuticle of cockroach.

BODY CAVITY

· The body cavity of the cockroach is a hemocoel filled with blood.

DIGESTIVE SYSTEM

· The alimentary canal is long and somewhat coiled, divisible into three main parts namely fore-gut, mid-gut, and hind-gut.
· Foregut (stomodaeum) is differentiated into five parts: buccal chamber, pharynx, oesophagus, crop, and gizzard.
· Gizzard is muscular and internally provided with six cuticular teeth which crush the food.
· A stomodaeal valve is present between gizzard and mesenteron.
· Midgut (mesenteron or ventriculus) is short, tubular, lined with glandular endoderm.
· At the anterior end of the mesenteron, there are eight blind glandular hepatic caeca that secrete digestive enzymes.
· Internally mesenteron is not lined by the cuticle but it is covered by a very thin and transparent peritrophic membrane formed of chitin and proteins.
· Peritrophic membrane is secreted by gizzard. It serves to protect the wall of the midgut from abrasion due to friction of food particles.
· Peritrophic membrane is permeable to digested food and enzymes in the mesenteron.
· Hindgut (proctodaeum) comprises the ileum, colon, and rectum.
· The wall of the rectum is provided with six rectal papillae, which help in the absorption of water and salts.
· Cockroach is omnivorous; it feeds on all sorts of organic debris.
· The digestive enzymes of saliva are mainly zymase and amylase.
· Most of the nutrients of food are digested in the crop.
· Absorption of digested food takes place in mesenteron.

CIRCULATORY SYSTEM

· Circulatory system of cockroach is open or lacunar type.
· The blood of the cockroach flows through the hemocoel system.
· Haemocoel is divided into a dorsal pericardial sinus, a middle perivisceral sinus, and a ventral perineural sinus by two perforated diaphragms.

A-C. Circulatory System of Cockroach

· The heart is longitudinally beaded with 13 chambers perforated by Ostia having valves.
· The heart is situated in the pericardial sinus over the dorsal diaphragm.
· The blood circulation is maintained by 13 pairs of wing-shaped involuntary alary muscles.
· Heart of cockroach is neurogenic (myogenic in frog, rabbit, and man).
· Blood of cockroach is colourless, consists of colourless plasma and corpuscles called 'hemocytes'.
· There is no respiratory pigment in hemolymph; the blood of the cockroach does not function as an oxygen carrier.
· In cockroaches oxygen is carried to individual cells without the participation of blood.
· All body tissues receive oxygen directly.

RESPIRATORY SYSTEM

· Respiratory system of the cockroach consists of the tracheal system.
· The tracheal system opens outside by ten pairs of spiracles (two pairs thoracic and eight pairs of abdominal). The spiracles are with valves.
· The first thoracic and first abdominal spiracles remain open all the time.
· The trachea is lined with spiral thickening of cuticle called intima which prevents the tracheal tubes from collapsing (The trachea of rabbit is also non-collapsible).
· Ventilation of the tracheal system is by alternate contraction and relaxation of the abdomen.

EXCRETORY SYSTEM

· Excretory organs of cockroach are Malpighian tubules open at the junction of midgut and hindgut (ileum).
· Malpighian tubules absorb excretory substances from hemolymph and fat bodies and pass into the proctodaeum.
· Malpighian tubules are concerned with homeostasis, osmoregulation, and excretion,
· Excretory products of cockroaches are uric acid and urates of sodium and potassium, so they are uricotelic.
· Fat body of cockroach contains mainly four types of cells, viz., trophocytes, mycetocytes, oenocytes, and urate cells.
· The trophocytes are most numerous containing reserve food in the form of fats, glycogen, and proteins.
· Mycetocytes contain symbiotic bacteria which help in the synthesis of some amino acids, vitamins, and glycogen from glucose.
· Oenocytes are supposed to help intermediary metabolism at the time of ecdysis.
· Urate cells absorb nitrogenous waste products from hemolymph and synthesize uric acid from these for storage.
· The fat body of the cockroach is functionally analogous to the liver of vertebrates.

NERVOUS SYSTEM

· Cockroach has a well-developed nervous system with central, peripheral, and sympathetic systems.
· Central nervous system consists of cerebral or supra oesophageal ganglion (brain); suboesophageal ganglion, paired circum-oesophageal connectives, double ventral nerve cord with three thoracic and six abdominal ganglia.
· The total number of ganglia in the ventral nerve cord of the cockroach is nine.
· Nerves given off to all parts of the body constitute the peripheral nervous system. For example, tegmina are supplied by a mesothoracic ganglion, anal styles, and copulatory appendages from the last abdominal ganglia.
· Sympathetic or stornatogastric nervous system includes five ganglia namely frontal (pharynx) hypocerebral (oesophagus), visceral or ingluvial (crop), and proventricular (gizzard).

ENDOCRINE SYSTEM

· Endocrine system of cockroaches consists of corpora allata, corpora cardiaca, and prothoracic gland.
· Intercerebral glands in the brain secrete the brain hormone.
· Brain hormone stimulates the prothoracic glands to secrete a moulting hormone called ecdysone.
· Corpora allata are neurosecretory and secrete juvenile hormone or neotinin.

SENSE ORGANS

· Sense organs in cockroach are, photoreceptors: compound and simple eyes), thigmoreceptors (antennae), chemoreceptors (on maxillary and labial palps, labium and hypopharynx), and auditory receptors on anal cerci.
· Each compound eye of cockroach is composed of about 2000 visual units called ommatidia.
· Each ommatidium is composed of a cuticular lens, two corneagen cells, a crystalline cone surrounded by four cone cells, a rhabdom surrounded by seven reticular ceils, and a basement membrane.
· There are two types of vision in insects, mosaic vision or apposition image during daytime and superposition or dull image in dim light.
· But in cockroaches, the pigment sheath of ommatidia is non-contractile so capable of only mosaic vision even during the night.
· Simple eyes of cockroach (fenestrae) comprise a single lens and is capable of perceiving only the light. Hence it is mainly concerned with light-collecting rather than image forming.

REPRODUCTION AND DEVELOPMENT

· In cockroaches, sexes are separate, so dioecious.
· Male organs consist of testes, vasa differentia, ejaculatory duct, mushroom or utricular gland, phallic or conglobate gland, and male gonapophyses.

Male reproductive system

Female reproductive system

· Testes of cockroach are located in the abdominal segments 4, 5, and 6.
· Mushroom gland consists of two types of tubules, the (i) long slender tubules, the utriculi majores or peripheral tubules, and (ii) short tubules, the utriculi breviores, making up of the major part of the gland.
· Small seminal vesicles are also found associated with mushroom gland.
· All sperms of a seminal vesicle are glued together into a large bundle called a spermatophore.
· Spermatophore has three-layered walls: inner layer secreted by utriculi majores; middle layer secreted by ejaculatory duct and outer layer secreted by the phallic gland.
· There are three asymmetrical chitinous structures called male gonapophyses or phallomeres. Right phallomere, left phallomere (largest), and ventral phallomere.

· Female organs consist of ovaries, oviducts, vagina, genital chamber, spermathecae, collateral glands, and female gonapophyses (ovipositor processes).
· Ovaries of cockroach are located in the abdominal segments 2 to 6.
· Each ovary consists of eight ovarioles.
· Two oviducts from each side open into a common oviduct or vagina which opens into the genital chamber by a female genital pore.
· A pair of spermathecae (left larger pyriform sac) is present near the female genital pore.
· Genital pouch or Genital pouch or gynatrium is divisible into a genital chamber in front and oothecal chamber behind.
· Female genitalia consist of 3 pairs of chitinous processes hanging from the roof of the oothecal chamber into its cavity.
· The egg of the cockroach is centrolecithal type, yolk being in the centre.
· Ootheca of cockroach contains sixteen fertilized eggs.
· Ootheca of cockroach is formed of a protein secreted by collateral glands.
· Nymph of cockroach emerges out from ootheca.
· A nymph resembles the adult in general structure but lacks the wings and mature reproductive organs.
· Metamorphosis in cockroaches is incomplete or paurometabolous type.
· Instar is a stage in the development of insects (larval instar, nymphal instar, etc.).
· Period between two moults in insects is termed stadium.
· Periplaneta americana has 11 nymphal instars in females and 12 nymphal instars in males.
· Blatta orientalis moults six times.
· Metamorphosis is regulated by two hormones, ecdysone secreted by prothoracic glands and juvenile hormone secreted by corpora allata.