In this article we will discuss about:- 1. Digestive System of Cockroach 2. Respiratory System of Cockroach 3. Circulatory System 4. Excretory System 5. Nervous System 6. Reproductive System.
Digestive System of Cockroach:
Digestive system of cockroach consists of the mouth parts, a long alimentary canal and a pair of salivary glands.
The alimentary canal consists of three parts namely:
Foregut or the stomodaeum is the first part of the alimentary canal. It is ectodermal in origin and lined by a cuticle. It includes the mouth, pharynx, oesophagus, crop and gizzard. Preoral cavity leads to mouth (preoral cavity is the cavity enclosed by mouth parts).
Mouth leads into a tubular pharynx from which arises a narrow, thin-walled, short oesophagus. The oesophagus is continued into a thin-walled sac-like dilatable crop. The crop leads into a small, thick-walled, muscular, pear shaped gizzard or proventriculus. It is highly specialised for grinding the food.
The gizzard contains an anterior armarium, middle pulvillus and posterior stomodeal valve. The inner lining of the armarium is raised into six chitinous powerful teeth, which form an efficient grinding apparatus.
There are backwardly directed bristles behind the teeth in the pulvillus which act as strainers and allow only fine particles to pass through. The stomodeal valve prevents the passage of food from midgut into the gizzard.
Midgut or ventriculus or mesenteron is the second part of the alimentary canal. It is situated between the Malpighian tubules (anterior) and hepatic caeca (posterior). It is endodermal in origin. It is in the form of a short narrow tube which is lined internally by endoderm. It is the main site of digestion and absorption.
Opening into the anterior end of the midgut, there are six to eight hepatic caecae (gastric caecae or enteric caecae or mesenteric caecae). They are short, finger-like, hollow and blind. They secrete digestive enzymes.
Hindgut or the proctodaeum is the last part of the alimentary canal. It is ectodermal in origin and lined by a cuticle.
It is long and divisible into:
(a) An anterior short, narrow ileum
(b) A middle long and wide colon and
(c) A terminal, short, dilated sac-like rectum which opens to the outside by the anus.
The rectum is thick-walled and its inner lining are produced into six prominent longitudinal ridges called rectal papillae. They help in absorbing water. At the junction of the midgut and the hindgut there are 100-150 thin, delicate, yellowish thread-like (or hair like) structures called the Malpighian tubules. They are excretory in function. The undigested material is eliminated as faeces through the anus in the form of slender pellets.
Respiratory System of Cockroach:
The respiratory system of cockroach consists of ectodermal air tubes or tracheae which communicate with the exterior by spiracles or stigmata. The haemocoel of cockroach contains a network of closed, elastic, branched air tubes called tracheae. There are three pairs of large, parallel longitudinal tracheal trunks one dorsal, one ventral and one lateral.
All these longitudinal tracheal trunks are interconnected by transverse commissures which anastomose to form a network. The tracheae have cuticular lining called intima or taenidia which form spiral or ring like thickening around the tracheae. These completely circular cuticular rings keep the tracheae distended and prevent the tracheae from collapsing even if there is no air in them.
Each trachea ends in a large terminal cell called tracheole cell or tracheal end cell from which arise very fine tubes called tracheoles. The tracheoles which are thin and less than 1 micron in diameter end blindly in the tissue cells. The elaborate tracheal system carries oxygen directly to all the body cells. This arrangement very well compensates for the inability of blood to transport oxygen due to the absence of a respiratory pigment.
In cockroach there are altogether ten pairs of segmentally arranged spiracles or stigmata of which two pairs are in the thorax and eight pairs in the abdomen. The thoracic spiracles are situated one pair between prothorax and mesothorax and the other between meso and metathorax. The abdominal spiracles are situated one pair in each of the first eight abdominal segments, between the terga and sterna. Each spiracle is a slit like aperture which is guarded by bristles or hairs to prevent the passage of dirt.
Circulatory System of Cockroach:
The circulatory system is of open type in cockroach. The viscera lie immersed in blood called haemolymph of the haemocoel or body cavity. Blood of cockroach is colourless as it has no haemoglobin pigments. The haemolymph does not help in respiration. There is a heart and aorta but no capillaries or veins.
Haemocoel is divided by a dorsal and ventral diaphragms into three blood filled sinuses-dorsal pericardial, middle perivisceral and ventral perineural. The diaphragms are with pores or fenestrae which permit the flow of blood from one sinus to another sinus. The ventral diaphragm enters the legs so that each leg contains perivisceral and perineural sinuses. In addition to the above three sinuses, there is one more sinus in the head.
Dorsal pericardial sinus encloses heart, aorta and one pair of alary muscles in each segment, one on either side of heart. The apices of these muscles are attached to the terga and their broad bases to the dorsal diaphragm. The perivisceral sinus contains the alimentary canal along with the whitish mass of tissue called fat body. The perineural sinus or sternal sinus encloses the ventral nerve cord.
The pulsatile heart of cockroach is a long narrow tube with anterior end open and posterior end closed. It is situated in the pericardial sinus mid-dorsally beneath the terga of thorax and abdomen. The heart consists of 13 funnel shaped chambers. Each chamber communicates with the one in front of it by a valvular opening.
The hinder part of each heart chamber has a pair of minute lateral openings called ostia which allow the haemolymph to flow in only one direction i.e., from pericardial sinus to the heart and not vice versa. Inside the heart the blood flows unidirectional from posterior end to the anterior end of the body.
The first chamber of the heart is continued anteriorly into an anterior aorta which opens into the head sinus.
The haemolymph circulates in the body cavity by the contraction and relaxation of the heart which is assisted by the alary muscles. The contraction of alary muscles results in the enlargement of pericardial sinus so that blood flows into it from the underlying perivisceral sinus. When the alary muscles relax, blood is forced through ostia into the heart. When the heart and aorta contract peristaltically from behind forwards the blood is driven into head sinus and then into the perivisceral and perineural sinuses. From the head sinus, blood flows into antennae in head and to wings through veins.
Heart → head sinus → perineural sinus → perivisceral sinus → pericardial sinus → heart.
Excretory System of Cockroach:
Malpighian tubules are the main excretory organs of cockroach. In addition, fat body cells, uricose glands, cuticle and nephrocytes also help in the process of excretion.
Malpighian tubules are the fine, long, unbranched, yellowish and blind tubules attached to the alimentary canal at the extreme anterior end of the hindgut. They are about 60 to 150 in number and are arranged in 6-8 bundles. Each tubule is about 16 mm in length and 0.5 mm in diameter. They lie freely in the haemolymph and are lined by glandular and ciliated epithelium.
They absorb nitrogenous waste products and convert them into uric acid. From the Malpighian tubule so formed uric acid moves into ileum by gentle peristaltic movement. More reabsorption of water takes place in colon and rectum so that more or less solid uric acid is eliminated with faeces through anus.
Nervous System of Cockroach:
The nervous system consists of the following:
i. Supra-Oesophageal Ganglion or Brain:
The supra-oesophageal ganglion or the cerebral ganglion is a bilobed structure formed by the fusion of three pairs of ganglia viz., proto, deuto and tritocerebrum. It is situated above the oesophagus almost between the bases of the antennae. It represents the brain which is chiefly concerned with sensory function. It gives off nerves to the antennae and eyes.
ii. Sub-Oesophageal Ganglion:
Sub-oesophageal ganglion is present below the oesophagus, posterior to the brain. It is also formed by the fusion of three pairs of ganglia – mandibular, maxillary and labial ganglia. It is the main motor centre. It gives off nerves to mandibles, maxillae and labium. It controls the movements of muscles of mouth parts.
The supra-oesophageal ganglion and the sub-oesophageal ganglion are connected by a pair of circum-oesophageal connectives or commissures which encircle the oesophagus. Thus, the supra-oesophageal ganglion, circum-oesophageal connectives and the sub-oesophageal ganglion together constitute the nerve ring around the oesophagus in the head capsule.
iii. Double Ventral Nerve Cord:
From the sub-oesophageal ganglion arises a double ventral nerve cord which runs through the thorax and abdomen below the alimentary canal upto the posterior end of the body. The nerve cords are solid. They run parallel and very close to each other. But they are fused at regular intervals in the thorax and abdomen to give rise to nerve ganglia.
There are three pairs of large ganglia in the thorax, one pair in each of the pro, meso and metathoracic segments. They are called the prothoracic, mesothoracic and metathoracic ganglia. The thoracic ganglia give off nerves to the muscles of the legs and wings. Similarly, there are six pairs of ganglia in the abdomen which lie in the first, second, third, fourth, fifth and seventh segments.
Each of these ganglia is formed by the fusion of two ganglia except the seventh. The seventh abdominal ganglion is the largest which is supposed to be formed by the fusion of three pairs of ganglia. The abdominal ganglia innervate dorsal and ventral muscles, heart, spiracles and reproductive organs.
The major sense organs of cockroach are antenneae, eyes, maxillary palps, labial palps, anal cerci etc. The compound eyes are situated on the dorsal surface of the head. Each eye consists of about 2000 hexagonal ommatidia. With the help of several ommatidia, a cockroach can receive several images at a time of an object. This kind of vision is known as mosaic vision with more sensitivity but less resolution, being common during night and hence called nocturnal vision.
Reproductive System of Cockroach:
In cockroach, the sexes are separate and there is a distinct sexual dimorphism.
Male Reproductive System:
The male reproductive system of cockroach consists of the following:
Situated amidst fat bodies between 4th and 6th abdominal segments dorsolaterally there is a pair of three lobed testes. Each testis consists of 30-40 small whitish transparent follicles in which the spermatozoa are formed. In young cockroaches these are well developed and functional while in adult ones they are non-functional and greatly reduced.
(b) Vasa Deferentia:
Arising from each testis, there is a vas deferens (pl., vasa deferentia). The two vasa deferentia, one from each testis, run posteriorly downwards and open into the ejaculatory duct through seminal vesicles. The sperms which are formed inside the testes are carried through the vasa deferentia and passed to the seminal vesicles.
(c) Ejaculatory Duct:
It is a single, median, wide, glandular and muscular duct which extends backward and opens into the genital pouch through the male genital pore. The latter lies immediately ventral to the anus, between 9th and 10th sterna. The glandular wall of the ejaculatory duct secretes the covering wall of spermatophore.
(d) Mushroom Shaped Gland or Utricular Gland:
The junction of two vasa deferentia and ejaculatory duct in 6th and 7th abdominal segments is surrounded by an accessory reproductive gland called mushroom shaped gland or utricular gland. The utricular gland is a large whitish gland which is made up of two kinds of glandular tubules – (i) the peripheral, long, slender tubules utriculi majores, whose secretion also forms the covering of spermatophore and (ii) the central, short tubules, utriculi breviores, whose secretion nourishes the sperms.
(e) Seminal Vesicles:
Present on the ventral surface of the anterior part of ejaculatory duct there is a sac formed of short bulbous tubules, called seminal vesicle. The sperms are stored in the seminal vesicles and are glued together in the form of bundles called spermatophores which are discharged during copulation.
(f) Phallic or Conglobate Gland:
It is a large, elongated, club-shaped accessory gland situated below the ejaculatory duct. Its narrow duct opens into the genital pouch by the side of male gonopore. The conglobate gland also secretes the covering of spermatophore.
(g) Genital Pouch:
The genital pouch in male cockroach is situated at the hind end of the abdomen bounded dorsally by the terga of 9th and 10th segments and ventrally by the sternum of 9th segment. It contains dorsal anus, ventral male genital pore and gonapophyses.
(h) External Genitalia or Gonapophyses:
Surrounding the male genital pore in the genital pouch there are three chitinous plates called phallomeres. The phallomeres together constitute the phallic organs or gonapophyses which help in copulation. Depending upon the position the phallomeres are classified into three types – right, left and ventral phallomeres.
Female Reproductive System:
The female reproductive system consists of the following:
One pair of yellow coloured ovaries are situated in 2nd to 6th segments, on either side of the hindgut embedded in fat bodies. Each ovary consists of 8 blind ovarian tubules or ovarioles inside which the linear series of ova are situated in an acropetal order (oldest at base and youngest at tip).
All the eight ovarioles of an ovary unite to form a short and wide lateral oviduct. The two lateral oviducts run backward and join to form a median common oviduct or vagina in the 7th segment.
The vagina which is the posterior wider part of the common oviduct opens into a large genital pouch by a vertical slit like vulva or female genital pore on the 8th sternum.
(d) Genital Pouch:
Genital pouch or gynatrium is a large boat shaped structure which is largely formed by the 7th sternum. The anterior and dorsal margins of the genital pouch are formed by the 8th and 9th sterna respectively while posterior, ventral and lateral margins are formed by the 7th sterna. The genital pouch can be divided into two parts. The anterior smaller part containing female gonopore and pores of spermathecae and collateral glands is called genital atrium or genital chamber, while the larger posterior part in which ootheca is formed is called oothecal chamber or vestibulum.
These are a pair of unequal sized structures where in the right spermatheca is narrow and tubular while left spermatheca is sac like. They are present in the 6th segment. The two spermathecae open by a median aperture in the dorsal wall of the genital pouch, at the tip of a small spermathecal papilla on 9th sternum. The spermathecae help in the storage of sperms received during copulation from the male.
(f) Collaterial Glands:
These are a pair of much branched accessory reproductive glands of female. These glands which are situated just behind the ovaries open into the genital pouch by two separate openings, lying close together, a little behind and above the spermathecal opening. The secretion of collateral glands helps in the formation of ootheca.
(g) External Genitalia:
Situated between the female genital pore and anus inside the genital pouch there are 3 pairs of chitinous plate like structures called gonapophyses. Of these one pair arises laterally from 8th sternum, while other two pairs arise from 9th sternum. These gonapophyses act as ovipositor valves. They help in copulation, egg-laying and in the formation of ootheca.
Sexually mature male and female cockroaches generally mate during nights from March to September months. The female cockroach secrets a pheromone or sex attractant which attracts the male cockroach. In response, the sexually excited male raises its forewing and rapidly flutters its hindwings.
In mating, first the male gets under female, extends his left hooked phallomere into the female genital chamber, clasping a small sclerite in front of ovipositor and then moves from beneath her. Both now get into end-to-end position. The process of copulation lasts for an hour or so, after which the male and female separate.
During copulation, spermatophore is deposited near the spermathecal pore by gonapophyses of male. Once the sperms migrate into the spermatheca, the spermatophore wall is dropped.
Each ovariole forms one mature ovum at a time. Altogether 16 eggs descend into the genital chamber. As they are laid they become fertilized by sperms ejaculated simultaneously from spermathecae. Fertilized eggs become hardened by the secretion of collaterial glands, which hardens to form an ootheca.
Ootheca is a dark reddish to blackish brown capsule. They are dropped or glued to a suitable surface, usually in a crack or crevice of high relative humidity near a food source. On an average a female cockroach produces 9-10 oothecae during her life time each containing 14-16 eggs arranged in two rows.
Development is direct, the nymphs look very much like adults and life history includes three stages – egg → nymph → adult. Nymphs are similar to the adult in morphology and physiology but are smaller in size, paler in colour, wingless and sexually immature. The nymph undergoes moulting about 13 times to become the adult. Thus development of cockroach is simple and direct with little metamorphosis (hemimetabola) and shows gradual metamorphosis or paurometaboly.
There are many species of cockroaches in the wild and are of least economic importance. A few species are found in and around human habitat, being pests they destroy food and contaminate it with their smelly excreta. They can transmit a variety of bacterial diseases by contaminating our food material.
Life Span of a Cockroach:
Seventy percent of females take 9 molting cycles to get to the adult stage and that represents (8 + 8 + 8.5 + 9 + 9.5 + 10 + 12 + 16 + 23) = 104 days. Such an adult female could live perhaps a year longer as an adult. All of this takes place at 30 C, the optimum temperature for growth and reproduction. If you wanted to slow it down you could lower the temp to 25 C and you would double all the times (approximately).
The adult female would take about 9 days to produce an ootheca containing about 12- 16 eggs. If the female had continuous food availability it could produce an ootheca every 2-3 days to 30 °C. The newly hatched larva weighs about 2 mg and doubles its weight at each larva-larva molt. So after molt 1 the larva weighs 4 mg, after molt 2 … 8 mg and so on.
How many breeding in lifetime?
Females of the American cockroach lay their eggs in a hardened, purse shaped egg case called an ootheca. About one week after mating the female produce an ootheca and at the peak of her reproductive period, she may form about two ootheca per week. The females on average produce an egg case about once a month for ten months laying 16 eggs per egg case.
The female deposits the ootheca near a source of food by either simply dropping it or gluing it to a surface with a secretion from her mouth. The deposited ootheca contains water sufficient for the eggs to develop without receiving additional water from the substrate. The egg case is brown when deposited and turns black in a day or two. A typical egg case contains about 14 to 16 eggs. It is about 8 mm long and 5 mm high.