Habit habitat and structure of Periplaneta americana.

Habit and Habitat.

They are found in places where there is warmth, dampness, and plenty of organic food to devour.The cockroach is nocturnal creatures. During daytime, they remain inactive and hiding. Their narrow and flattened body is adapted to slip into narrow creeks and crevices. During night, they show much activity and run here and there in search of food.

In warmth months, cockroaches are common outdoors, occurring in the sewer, manholes, dumps, outbuildings, and wood piles. Indoors, they are common pests in kitchen, latrines, hotels, restaurants, storerooms, board ships etc. The Oriental cockroach prefers somewhat cooler places and hence it is commonly found in toilets and behind baths and sinks. These animal are cursorial insects, i,e fast runners, and rarely resort to flight. It has been reported that at 25 D C , Cockroach runs from 70-130 cm per seconds. Being omnivorous and scavengers in diet, they devour any animal or vegetables and even non-living materials like leather, paper, cloth, etc causing great loss.

An external feature of the Cockroach.

(a) Shape, Size and colour of Cockroach.

The body of cockroach is narrow, elongated, bilaterally symmetrical, compressed dorsoventrally, flattened. The adult measure about 2to 4 cm in length and about 1 cm in width. Colour is reddish-brown or shiny with a pale yellow area around the edge of tergum of pronotum of prothorax and the two dark patches over it.The two dark patches surrounded by a light-brown margin in the first thoracic segments.

(b) Exoskeleton or cuticle.

The entire body of cockroach is covered externally by a non-living brown coloured, hard, jointed, and chitinous exoskeleton.composed of several plates or sclerites. The exoskeleton of each segment has four separate sclerites which are joined together by delicate and elastic articular membrane. The sclerites of the dorsal side are called tergite, of ventral side, are called sternite and those of lateral sides are called pleuritis. The exoskeleton, in fact, consists of a thick and strong chitinous cuticle which provides protection to the body, prevents unnecessary water loss and points for the attachments of muscles. It wall is secreted by the underlying the hypodermis.

( c) Segmentation.

It shows clear cut segmentation in its body except the head. The thorax consists of three segments and abdomen ten segments in adults which were eleven in an 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 adults remains only 19 as said above.

(d) Division of body.'

The body is distinctly divided into segments. These are grouped into well-defined regions or tegmata.

(i) head, (ii) thorax, (iii) abdomen.

(e) Head.

It is flattened, oval, small, pear-shaped, roughly triangular, anteroposteriorly and lies at right angles to the longitudinal body axis.It is highly mobile in all directions due to the flexible neck.It is formed by the fusion of 6 embryogenic segments.The tergites of these segments have fused to form a head capsule. The head bears a pair of compound eye, a pair of antennae and appendages around the mouth. It is divided into three regions

.(i).Neck.

(ii) The exoskeleton of a head.

(iii) Appendages of a head.

(i) Neck.

The head is attached to thorax anteriorly by a short and narrow neck or cervical.It is supported by four small chitinous plates, 2 dorsal and 2 ventral. The neck has muscular retract and protract the head and turns it up or down of from side to side. The cockroach can also stretch its head like other insects.

(iii) The exoskeleton of a head.

The whole head is covered by the number of chitinous plates or sclerites, constituting its exoskeleton or head.Their fused margin is visible as lines, called sutures. Top of the vertex of the head is formed by two epicranial plates joined in front by an inverted Y-shaped coronal or epicranial suture.The unpaired triangular frons lies between the arm of the rectangular clypeus form the lower part of the face. The two lateral sides of head below compound eyes are formed by the cheeks or genae.

(iii) Appendages of a head.

Head bears a number of jointed appendages. On each dorsolateral side of the head is a large reniform and black compound eye. Just it fronts of each eye is a long.slender and multi-segmented antenna. Inner to the base of each antenna is small rounded and whitish area or fenestra, a representing a simple eye or ocellus. The lower end of head bears the preoral cavity and mouth, surrounded by mouth parts. These consists of the labrum, mandible maxillae, labium, and hypopharynx. Such a head with mouthparts directed downwards is called hypognathous.

(f) Thorax.

The middle regions of body or thorax consists of 3 distinct segments called. From in front backwards, the prothorax mesothorax and metathorax. The prothorax segment is the largest and due to the presence of the three pairs of walking legs, it is also called hexapods.Eash segments present in the thorax bears a pair of walking legs and the first pair of wings arise from the mesothorax, while the second pair from the metathorax. The prothorax has a large pronotum, its anterior margin overlaps the retracted head and the posterior margin covers the bases of the wings. The mesonotum and metanotum are smaller, they are flat and rectangular with irregular lateral margins. The thoracic pleura are divided into two parts each by a verticle groove, they are an epimeron and an episternum.

The exoskeleton of each thoracic segment is formed by four chitinous sclerites, a dorsal tergite or tergum , laterally each side has a pleurite or pleuron and ventrally there is a sternite or sternum. Between the sclerites of adjacent segments are soft, thin flexible articular or arthrodial membranes which join the sclerites.

Ventrally, the thorax is largely membranous, but in each segment, the sternum is in the form of to one anterior and the other posterior.

(g) Abdomen.

Abdomen consists of ten segments. The exoskeleton of the abdomen is formed of hardened sclerites. A typical abdomen segment has a dorsal tergum, ventral sternum and between them a narrow membranous pleuron on each side. Each pleuron has three sclerites, two lateral-tergites arising from the tergum, and arising from the sternum is a narrow lateral-sternite.Dorsally, the abdomen has 10 terga, but has 9^th tergum of the male and the 8^th and 9^th terga of the female are largely covered by the 7^th tergum.

The membrane between the 5^th and 6^th abdominal terga forms two deep pockets in the male, each pocket gas 2 slit-like pouches which are probably glandular and produce a secretion which is probably glandular and produces a secretion which excites the female for copulation in the breeding season. This is called stink glands.The 8^th and 9^th sterna of the female have been imagined inwards to form a chamber-like gymnatorium whose posterior part constitutes the oothecal chamber because ootheca or cocoons are formed in it. In a male, a group of the genital structure may slightly protect from the end of the abdomen. The 9^th sternum of the male has a pair of slender anal styles which are absent in female in which the 7^th sternum is produced backwards onto a pair of large oval apical lobes or nonvalvular plates which form a keel-like structure. This rounded keel at once distinguishes the female from the male.

The 10^th tergum is shield-shaped with a deep cleft posteriorly. The 10^th tergum bears a pair of long, tapering anal cervix which is fifteen joined. Each cerus is transversed by a nerve and 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 a female.

The genital apertures of both sexes are surrounded by sclerites called gonapophyses.In the male, the gonapophyses belong to the 9^th segment and they form the external genitalia. In the female, the gonapophyses belong to the 8^th and 9^th segments and they form an ovipositor.In the 10 segments just below the tergum is an anus supported by four podical plates which represent the vestiges of the 11^th segment and cerci are actually the appendages of this 11 segment. The podical plates from four lobes, one on each side of the anus are called paraproducts, above the anus, is a rounded periproct, and below the anus is a small hypo proact.

Some worker suggests that the secretion of these glands possesses a characterised odour which is probably repulsive for the enemies and helps the female in detecting the presence of its mate. The male genital apertures are situated between the 9^th and 10^th sterna, while the female genital aperture is situated on the 8^th sternum.

Reference.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

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