Respiratory system in insect
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The respiratory system of insects involves a network of tubular structures called trachea that distribute oxygen throughout the body. Trachea branch into very fine tracheoles that penetrate tissues and supply oxygen. Trachea are composed of a spiral thickening called taenidia that provides support. They open to the outside through spiracles located on the thorax and abdomen. Spiracles allow gas exchange and can close to prevent water loss. Trachea branch and connect to form a dorsal, ventral and two lateral trunks that supply different body regions. Respiration is classified based on the number and location of functional spiracles. Some insects respire through other structures like gills or cuticular surfaces in the absence of
Respiratory system in insect
- 1. Prepared by: Vidya K. C Suresh R. Jambagi M.Sc. (Agri) Agril. Entomology University of Agricultural Sciences Dharwad, Karnataka-580005 Email: jambagisuru@gmail.com GENERAL ENTOMOLOGY Presentation: 5 Topics : Respiratory system in insects
- 2. Tracheal system: In insects, exchange of gases takes place through tubular structures, called trachea. They are distributed throughout the body collectively forming tracheal system. These trachea open outside on the body wall through small openings called spiracles. Spiracles occur on the pleural surfaces of the body, one on either side of each segment. The tracheae are divided in to very fine branches known as tracheoles. They supply oxygen to the body tissues. The tracheal system with functional spiracles is called the open tracheal system and with non-functional spiracles is called closed tracheal system. RESPIRATORY SYSTEM Suresh Jambagi M.Sc (Agri) UAS Dharwad 2
- 3. Tracheae are fine elastic tubular structures which are ectodermal in origin. They consist of cuticle, epidermis, basement membrane as in case of general body wall but arranged in reverse manner, i.e. basement membrane forms the outermost coat of trachea. The inner cuticular lining forms the intima inside. Tracheae are circular or elliptical in their cross section. The cuticular lining (intima) appear as a spiral thickening throughout the length of the tube of trachea. These spiral thickenings are known as ‘taenidia’ which give support to the trachea without being collapsed when there is no air. Suresh Jambagi M.Sc (Agri) UAS Dharwad 3
- 4. It consists of chitin, resilin in protein-chitin matrix. The trachea ramify into very fine branches known as ‘tracheoles’ which are about 0.1 – 1 μm in diameter (Fig. 32). These tracheoles are formed in to cells called ‘tracheoblast’ or tracheolar end cell, which are derived from epidermal cells, lining the trachea. Tracheoles form a network over the visceral organs including the alimentary canal as well as the gonads (ovaries, testis) and penetrate in to the tissues of the organs and become intracellular and supply oxygen directly to the tissues. Suresh Jambagi M.Sc (Agri) UAS Dharwad 4
- 5. Differences between trachea and tracheoles Trachea • These are large tubes running from spiracles • Taenidia present • Intima layer is shed during moulting • Never become intracellular • The intima layer consist of protein – • chitin matrix with resilin Tracheoles • Fine tubes arising distally from trachea • Absent • Intima layer is retained, unchanged during moulting • Intracellular • Chitin – protein matrix present, resilin absent Suresh Jambagi M.Sc (Agri) UAS Dharwad 5
- 6. Tracheal trunks: The trachea coming from spiracles through out the body join with those of neighbouring spiracles forming ‘longitudinal trunks’. Likewise, these tracheae by combining with those coming from dorsal, lateral and ventral sides of the body fuse to form transverse commissures and longitudinal connectives. All these in total form into dorsal trunk, lateral trunks which are two in number and one ventral trunk. The dorsal trunk supply oxygen to proximal part of the body as well as to heart where as the ventral supplies to the central nervous system. The two lateral longitudinal trunks spread tracheoles to alimentary canal, legs, gonads and wings. As the head do not contain spiracles, air is supplied through the first pair spiracles by means of two main branches of the dorsal longitudinal trunk, where one branch supply O2 to eyes, antenna, brain; other branch to mouthparts and muscles of the head. Suresh Jambagi M.Sc (Agri) UAS Dharwad 6
- 7. Spiracles: They are the openings of the internal tubular trachea. Except in Diplura, in all the orders, spiracles are absent in prothorax and distributed in meso, metathorax and abdomen. A total of 10 pairs are present in general, 2 pairs in thorax and 8 pairs in abdomen. Spiracles are situated on pleural surface. They consist of a small ring like sclerite at opening called ‘peritreme’ leading to a cavity known as ‘atrium’. The closing and opening of spiracles is accompanied by atrial valve lined with fibrous processes and form so called felt chamber which reduces water loss in the absence of closing mechanism. In some dipterans, coleopterans, lepidopterans, spiracles consists of sieve plate containing large number of small apertures through which gas exchange takes place. This modification is to prevent entry of water especially in aquatic forms. In most of the terrestrial insects, water loss through spiracles is controlled by the closing mechanism which consists of one or two valves or a constriction from the trachea or by muscular activity. The hydrophobic nature of spiracles is also due to the presence of modified epidermal glands known as peristigmatic glands which secrete a hydrophobe material preventing the wetting of these organs. Suresh Jambagi M.Sc (Agri) UAS Dharwad 7
- 8. Classification of tracheal system based on number and arrangement of functional spiracles In most of the insects, 10 pairs of spiracles are present. Some of the modifications are as follows I. Holopneustic: These are primitive type with 2 pairs of spiracles on thorax and 8 pairs on abdomen. All the spiracles are functional. 1 + 1 + 8. Ex: Dragonflies, Grasshoppers and Cockroach II. Hemipneustic: One or more pairs of spiracles become non-functional. They are a) Peripneustic: Metathoracic spiracle is closed. 1 + 0 + 8. Ex: larvae of Lepidoptera, Hymenoptera, Coleoptera. b) Amphipneustic: Only mesothoracic and last pair of abdominal spiracles are open. 1+0+ 1. Ex: larva of cyclorrhaphan Diptera. c) Propneustic: Only one pair i.e. mesothoracic spiracles are open, 1 + 0 + 0 Ex: mosquito pupa d) Metapneustic: Only last pair of abdominal spiracles are open. 0 + 0 + 1. Ex: mosquito larvae e) Apneustic: No functional spiracles. Ex: mayfly larva, nymph of Odonata Suresh Jambagi M.Sc (Agri) UAS Dharwad 8
- 9. III. Hypopneustic: 1 or 2 pairs of spiracles may completely disappear or absent Ex: Siphunculata, Mallophaga IV. Hyperpneustic: More than 10 pairs of spiracles are present Ex: Japyx sps. (dipluran) Other types of respiration: 1. Cutaneous respiration: When the spiracles are absent, respiration occurs through body wall which forms main source for gaseous exchange. Ex: Protura, Collembola and endoparasitic insects. 2. Tracheal gills: Also called as abdominal gills which occur as the outgrowths of the trachea in the form of gills distributed on the lateral sides of the body. They are useful for absorption of dissolved oxygen. They may vary in shape as lamellate or filamentous. Ex: larva of Trichoptera, nymphs of Ephemeroptera 3. Spiracular gills: Peritreme or atrium of spiracles is drawn out in to a long filament like structure known as spiracular gills. These gills are adapted for both aquatic and aerial respiration, enabling the insect to live in air and moist places or completely in water or at the edges of water structures. Ex: In some aquatic pupae Suresh Jambagi M.Sc (Agri) UAS Dharwad 9
- 10. 4. Blood gills: These are tubular or digitiform or eversible structures present at the anal end of body ranging from 4-6 in larva of Trichoptera. In chironomid larva of Diptera, 2 pairs of blood gills are present on penultimate segment and a group of 4 shorter anal gills are present. These are called blood gills as they contain blood but some times have trachea. Function of these structures is the absorption of water and inorganic ions rather than respiration. 5. Rectal gills: In dragonfly nymphs (naiads), the rectum modifies in to a barrel like chamber where the rectal wall forms in to basal thick pads and distal gill filaments which are richly supplied with tracheoles. They help in respiration. 6. Air sacs: In many winged insects, the trachea get dilated at some points to form thin walled air sacs which do not contain the taenidia. These can be seen as glistening sac like structures mainly function as storage structures of air which change their volume with respiratory movement. 7. Plastron respiration: The plastron is a special type of air store in the form of a thin film held by a system of hydrofuge hairs, scales or other cuticular processes whose volume remains constant. If there is adequate oxygen dissolved in water, the plastron can act as a permanent physical gill. The trachea opens in to plastron. Ex: aquatic beetles. Suresh Jambagi M.Sc (Agri) UAS Dharwad 10