Life cycle and economic importance of Periplaneta americana.

Life cycle in Periplaneta Americana.

Copulation.

It occurs during the night. During copulation, the male cockroach They finda suitable mate and then two partners come together by thin posterior ends. The male opens the nonvalvular plates of the female by its titillation and inserts its phallomeres into the genital chamber of the female. The active breeding season of the cockroach starts from March and it lasts up to September. The pseudopenis of the male is then inserted into the gonopore of female and rotated transversely to hold it in position. The anterior gonapophyses of the ovipositor are held by the right phallomere. Ventral phallomere moves to the right, thus, opening the gonopore of the ejaculatory duct, then , Spermatophore is expelled and it was deposited directly on the spermathecal papilla to which it is fixed in about an hour.Phallic gland now pours its secretion on the spermatophore to form its outermost covering which hardens in about 2 hours. Copulation lasts for about an hour and a quarter, after which two cockroaches separate. The sperms pass from the spermatophore into the spermatheca slowly in the course of the next 20 hours after which the empty spermatophore is discarded.

Formation of Ootheca.

The eggs come alternately from the two ovaries into the common oviduct and pass through the female gonopore into the genital chamber where they are fertilised by sperms coming from the spermathecae. The two collateral glands pour their different secretions on the fertilised eggs, these secretions combine to form a scleroprotein which hardens to around the eggs.The ootheca is shaped and moulded by the ovipositor and the walls of the oothecal chamber. The ootheca is 12mm in length, on one side it has a straight crest ith a serrated margin, it contains 16 fertilised eggs standing vertically in two rows, the position of eggs can be seen on the outer surface of ootheca. The ootheca is completed in about a day and it protrudes from the oothecal chamber, being held in place by the 10^th tergum and nonvalvular plates. The female cockroach carries the 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 1 or 2 years.

The egg of cockroach, like other insects, are called centrolecithal because the ooplasm is placed in the form of a thin film outside a central mass of yolk. The embryonic development occurs in the ootheca, which takes nearly 5 to 13 weeks.After the embryonic development is complete, the ootheca ruptures and the young ones hatch out.The young ones of cockroach resemble their parents in every except that they are smaller in size and without wings. These are called nymphs which undergo metamorphosis.

Metamorphosis in Cockroach.

The nymph of cockroach which resembles its adult in structure and feeding the habit, but it is paler in colour, smaller in size, devoid of wings and the gonads and the gonads are immature. AS it feeds it grows, its outer exoskeleton is cast off, and this process of shedding the exoskeleton is known as moulting or ecdysis which is controlled by the hormonal activity. During ecdysis, the hypodermis of the integument secretes an enzyme which erodes the lower surface of the old cuticle, thus, separating the cuticle from the hypodermis. Then the hypodermis secretes a new epicuticle which is impervious to the enzyme. Finally, the hypodermis secretes a new procuticle. The epicuticle and procuticle form a new cuticle. The old cuticle is ruptured and is shed by the animal. Thus, the nymph forms a new exoskeleton by its hypodermis before the old one is cast off and growth can take place only before the new covering has hardened because the tough exoskeleton does not allow an increase in size.The cockroach nymph undergoes ten to twelve ecdyses to become an adult about a year. During this period the nymph grows, wings are formed from the integument and gonads become mature. The ecdysis is thus, closely associated with the growth also. However, summing up the growth processes it can be said that nymph gradually develops further and further from ecdysis to ecdysis. After the last ecdysis no further increase in the size, i.e growth occurs. This gradual assumption of adult characters with hardly any change is called paurornetabolic metamorphosis.

The Economic importance of Cockroach.

Cockroach becomes a public health problem because of their association with human waste and disease, and their ability to move from the sewers into homes and commercial establishments. At least 22 species of the pathogenic human bacteria, virus, and protozoans, as well as five species of helminthic worm, have been isolated from the field collecting American cockroaches. Cockroaches are also aesthetically displeasing because they are soil items with their excrement and regurgitation.They are mainly found in caves, mines, latrines, cesspools, sewers, sewerage treatment plants, and dumps. Their presence in these habits is of epidemiological significance.

Reference.

Aggarwal Sarita. A Text Book of Biology, New Delhi.: Madhuban Educational Books, 2011.

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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