Cockroach

  • Cockroaches are brown or black-bodied animals that are included in the class Insecta of ==Phylum Arthropoda.==
  • Bright yellow, red, and green-coloured cockroaches have also been reported in ==tropical regions.==
  • Their size ranges from ¼ inches to 3 inches (0.6-7.6 cm) and has ==long antennae, legs, and a flat extension of the upper body wall that conceals the head.==
  • They are ==nocturnal omnivores that live in damp places throughout the world.==
  • They have become residents of human homes and thus are serious pests and vectors of several diseases

Morphology:

  • The adults of the common species of cockroach, %%Periplaneta americana are about 34-53 mm long with wings that extend beyond the tip of the abdomen in males%%.
  • The body of the cockroach is ^^segmented^^ and divisible into three distinct regions – head, thorax, and abdomen.
  • The entire body is covered by a ^^hard chitinous exoskeleton (brown in colour).^^
  • In each segment, the exoskeleton has %%hardened plates called sclerites (tergites dorsally and sternites ventrally) that are joined to each other by a thin and flexible articular membrane (arthrodial membrane).%%
  • The %%Head is triangular in shape%% and lies anteriorly at right angles to the longitudinal body axis.
  • It is formed by the ^^fusion of six segments and shows great mobility^^ in all directions due to a flexible neck.
  • The head capsule bears a %%pair of compound eyes.%%
  • A pair of ^^thread-like antennae^^ arise from membranous sockets lying in front of the eyes.
    • %%Antennae have sensory receptors that help in monitoring the environment.%%
  • The anterior end of the head bears appendages forming %%biting and chewing-type mouthparts.%%
  • The mouthparts consist of a l%%abrum (upper lip), a pair of mandibles, a pair of maxillae, and a labium (lower lip).%%
  • A median flexible lobe, acting as the ^^tongue (hypopharynx),^^ lies within the cavity enclosed by the mouthparts.
  • Thorax consists of three parts – prothorax, mesothorax, and metathorax.
    • The head is connected with the thorax by a short extension of the ^^prothorax^^ known as the neck.
    • Each thoracic segment bears a pair of walking legs.
    • The ^^first pair of wings arise from the mesothorax and the second pair is from the metathorax.^^
    • %%Forewings (mesothoracic) called tegmina%% are opaque dark and leathery and cover the hind wings when at rest.
    • The ^^hind wings^^ are transparent, and membranous, and are used in flight.
  • The %%abdomen%% in both males and females consists of %%10 segments.%%
    • In females, ^^the 7th sternum is boat-shaped and together with the 8th and 9th sterna forms a brood or genital pouch whose anterior part contains female gonopore, spermathecal pores, and collateral glands.^^
    • In males, %%the genital pouch or chamber lies at the hind end of the abdomen bounded dorsally by the 9th and 10th terga and ventrally by the 9th sternum.%%
    • It contains the dorsal anus, ventral male genital pore, and gonapophysis.
    • Males bear a pair of ^^short, threadlike anal styles which are absent in females.^^
  • In both sexes, the %%10th segment bears a pair of jointed filamentous structures called anal cerci.%%

Anatomy:

  • The alimentary canal present in the body cavity is divided into three regions:
    • foregut
    • midgut
    • hindgut.
  • The ==mouth opens into a short tubular pharynx, leading to a narrow tubular passage called the oesophagus.==
    • This in turn opens into a ==sac-like structure called a crop used for storing food.==
    • The ==crop is followed by gizzard or proventriculus.==
    • ==It has an outer layer of thick circular muscles and a thick inner cuticle forming six highly chitinous plates called teeth.==
    • ==Gizzard helps in grinding the food particles.==
  • The entire ==foregut is lined by cuticles.==
  • A ring of 6-8 blind tubules called ==hepatic or gastric caeca is present at the junction of foregut and midgut, which secrete digestive juice.==
  • At the junction of midgut and hindgut is present another ring of 100-150 ==yellow-coloured thin filamentous Malpighian tubules.==
    • They help in the ==removal of excretory products from the haemolymph.==
  • The ==hindgut is broader than the midgut and is differentiated into the ileum, colon, and rectum==.
  • The ==rectum opens out through the anus.==
  • The blood vascular system of the cockroach is an ==open type.==
  • Blood vessels are poorly developed and open into space ==(haemocoel).==
  • Visceral organs located in the haemocoel are bathed in blood ==(haemolymph).==
  • The haemolymph is composed of colourless plasma and haemocytes.
  • The heart of the cockroach consists of an ==elongated muscular tube lying along the mid-dorsal line of the thorax and abdomen.==
  • It is differentiated into funnel-shaped chambers with ==Ostia== on either side.
  • Blood from the sinuses enters the heart through ostia and is pumped anteriorly to the sinuses again.
  • The respiratory system consists of a network of the trachea, that opens through ==10 pairs of small holes called spiracles present on the lateral side of the body.==
  • Thin branching tubes (tracheal tubes subdivided into tracheoles) carry oxygen from the air to all the parts.
  • The opening of the spiracles is regulated by the ==sphincters.==
  • ==The exchange of gases takes place at the tracheoles by diffusion.==
  • ==Excretion is performed by Malpighian tubules.==
    • Each tubule is lined by ==glandular and ciliated cells.==
    • They absorb nitrogenous waste products and convert them into ==uric acid which is excreted out through the hindgut.==
    • Therefore, this insect is called ==uricotelic.==
    • In addition, the ==fat body, nephrocytes and urecose glands also help in excretion.==
  • The nervous system of cockroaches consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.
    • ==Three ganglia lie in the thorax, and six in the abdomen.==
  • The nervous system of cockroaches is spread throughout the body.
  • The head holds a bit of a nervous system while the rest is situated along the ventral (belly-side) part of its body.
  • So, now you understand that if the head of a cockroach is cut off, it will still live for as long as one week.
  • In the head region, ==the brain is represented by supra-oesophageal ganglion which supplies nerves to antennae and compound eyes.==
  • ==In cockroaches, the sense organs are antennae, eyes, maxillary palps, labial palps, anal cerci, etc.==
    • The compound eyes are situated at the dorsal surface of the head.
    • ==Each eye consists of about 2000 hexagonal ommatidia== (sing.: ommatidium).
      • With the help of several ommatidia, a cockroach can receive several images of an object.
      • ==This kind of vision is known as mosaic vision== with more sensitivity but less resolution, being common during the night (hence called ==nocturnal vision==).
  • Cockroaches are dioecious and both sexes have well-developed reproductive organs.
  • The male reproductive system consists of a pair of ==testes one lying on each lateral side in the 4th -6th abdominal segments.==
  • From each testis arises a thin vas deferens, which opens into the ejaculatory duct through the seminal vesicle.
  • The ==ejaculatory duct opens into the male gonopore situated ventral to the anus.==
  • A characteristic ==mushroom-shaped gland is present in the 6th-7th abdominal segments== which ==function as an accessory reproductive gland.==
  • The external genitalia is represented by male gonapophysis or phallomere (==chitinous asymmetrical structures, surrounding the male gonopore==).
  • The sperms are stored in the seminal vesicles and are glued together in the form of bundles called spermatophores which are discharged during copulation.
  • The female reproductive system consists of two large ovaries, lying laterally in ==the 2nd – 6th abdominal segments.==
    • Each ovary is formed of a group of ==eight ovarian tubules or ovarioles,== containing a chain of developing ova.
    • ==Oviducts of each ovary unite into a single median oviduct (also called vagina)== which opens into the genital chamber.
      • ==A pair of spermatheca is present in the 6th segment which opens into the genital chamber.==
    • Sperms are transferred through spermatophores.
    • Their fertilised eggs are encased in capsules called ==oothecae.==
    • The ootheca is a dark reddish to blackish brown capsule, about 3/8" (8 mm) long.
    • They are dropped or glued to a suitable surface, usually in a crack or crevice of high relative humidity near a food source.
    • On average, ==females produce 9-10 oothecae, each containing 14-16 eggs.==
  • The ==development of P. americana is paurometabolous, meaning there is development through the nymphal stage.==
  • The nymphs look very much like adults.
    • The nymph grows by moulting about 13 times to reach the adult form.
    • The ==next to last nymphal stage has wing pads but only adult cockroaches have wings.==
  • Many species of cockroaches are wild and are of no known economic importance yet.
  • A few species ==thrive in and around the human habitat.==
  • They are pests because ==they spoil food and contaminate it with their smelly excreta.==
  • They can transmit a variety of bacterial diseases by contaminating food material.