Respiratory system of Insects

Respiratory system

1.                                                  ASSIGNMENT                                                on                      Anatomy and Physiology of Respiratory System       (ENT.502 : INSECT ANATOMY AND PHYSIOLOGY ) Submitted By: Gurpinder Singh M.Sc. Entomology  L-2020-A-52-M Submitted To:                         Dr. Kamaljeet Singh Suri (Principal Entomologist) Dr. Anureet Kaur  Professor (Entomology)

2. RESPIRATORY SYSTEM IN INSECTS

3. INTRODUCTION  Insects must obtain oxygen from their environment and eliminate carbon dioxide respired by their cells.  This gas exchange occurs by means of internal air filled tubes . Respiratory system of Insects  is ectodermal in origin. Unlike humans blood is usually not involved in Respiration.

4. Respiration includes Two Phases 

5. 1 . Physical Phase  It includes Oxygen transport and removal of carbon dioxide  2 .Chemical Phase  It includes Oxidation of Carbhohydrates  resulting in formation of Carbon dioxide and water

6. COMPONENTS OF RESPIRATORY SYSTEM

7. Spiracle  External opening , in their exoskeletons present on lower side of Tergum . chamber or atrium with  a  opening and closing mechanism called Atrial valve. surrounded by a Sclerite called  Peritreme .  Peristgmatic  glands present around the spiracle that prevents the wetting of organ.                                                                                                                                                                                   Spiracle 

8. Types of Spiracles Simple or non- Atriate : An opening with no lip closure or filter chamber.  Atriate with lip closure : Slit like apparatus with two movable valves/lips. Atriate with filter-apparatus : Atrium is lined with tiny hairs.

9. Based on number and arrangement of functional spiracles A. Polypneustic : (at least 8 pair of functional spiracles       on each side of body ) 1. Holopneustic:10 pairs, 2 in thorax and 8 in abdomen. e.g. grasshopper  2. Hemipneustic : Out of 10 pairs, one or two non-functional  3. Peripneustic : 9 pairs - 1 in thorax 8 in abdomen e.g. Caterpillar  1 -  Holopneutic 2- Hemipneustic 3-Peripneustic

10. Based on number and arrangement of functional spiracles B. Oligopneustic  (1 or 2 pair of functional spiracles in each side of the body ) 4.Amphipneustic 2 pairs - One anterior, one posterior, e.g. maggot. ​ 5.  Propneustic : 1 pair -anterior pair e.g. Puparium  ​ 6.  Metapneustic : 1 pair - posterior pair e.g. Wriggler ​ 4.Amphipneustic 5.  Propneustic   6.  Metapneustic

11. Based on number and arrangement of functional spiracles C. Hypopneustic :10 pairs - 7 functional (1 thorax +6 abdominal), 3  non functional . e.g. head louse   D. Apneustic:  All spiracles closed, closed tracheal system e.g. naiad of may fly.          Mosquito larva           mayfly  naid            Dragonfly naid              

12. Based on number and arrangement of functional spiracles E.  Hyperpneustic  : contains 11 pairs of spiracles (2 pairs in mesothorax , 1 pair metathorax, 8 pairs in abdomen ) Ex.  Diplura  ( Japygids ) IN quiescent stage , only 1st and 10th spiracle is open ( Amphipneustic )

13. Tracheae

14. TRACHEOLES  It is less than 1 micrometer  in diameter  end blindly and closely contact the respiring tissues.  Gaseous exchange occurs across tracheoles.

15. Differences between trachea and tracheoles:                           Trachea                        Tracheoles These are large tubes running from spiracles Fine tubes arising distally from trachea Intima layer is shed during moulting Intima layer is retained, unchanged during moulting Never become intracellular Intracellular

16. Mechanism of respiration

17. AIRSACS In trachea thin walled , balloon-like structures acts as oxygen reservoir. (where taenidia is absent )

18. Functions of Air Sacs  Provide buoyancy to flying  & aquatic insects. In dry terrestrial environments , it allows an insect to conserve water by closing its spiracles  during periods of high evaporative stress. Act as sound  resonater and heat insulator  Provide space for growing organs 

19. Collembola ,  Archaeognatha  have  tracheae from each spiracle form a tuft which remains separate from the tufts of other spiracles.  In the majority of insects, however, the tracheae from neighboring spiracles join to form longitudinal trunks running the length of the body.

20. Longitudinal Trunks  Dorsal l ongitudinal Trunks    (Heart, Dorsal Muscles etc.) Ventral l ongitudinal Trunk    (Central Nervous System) Lateral longitudinal Trunks      (Alimentary canal,Gonads,Wings  ,legs etc.) Visceral  l ongitudinal Trunk     (Alimentary canal)

21. Air flow types  Two types Tidal (in and out of the same spiracles) Directed (inflow through anterior spiracles and outflow through posterior abdominal ones.) Interconnecting longitudinal and transverse tracheal trunks make directed flow possible and more efficient than tidal flow, because the system is constantly flushed and incoming air is not mixed with used air.

22. Moulting of Tracheal System During moulting  , Intima layer of Trachea is shed while of tracheoles remains intact. Prior to the molt, the epithelial layer of the tracheae increases in size A new cuticle is formed under the old cuticle.  Molting fluid fills the space between the new and old cuticle, and the old cuticle detaches . The old cuticle is pulled out of the tracheae through the spiracles with the rest of the exuvia , and the molting fluid is reabsorbed.

23. Functioning of Repiratory System

24. A one-muscle spiracle; second thoracic spiracle of a locust ( Schistocerca ) (after Miller, 1960a). (a) External view; (b) internal view; (c) diagrammatic section through the spiracle showing how movement of the mesepimeron (arrow) causes the valves to open wide (dotted).

25. Control of Spiracle opening  By CNS (Central Nervous System) & local Stimuli If dry conditions , spiracle remain closed for long time.

26. Gaseous Exchange In Terrestrial Insects :

27. Diffusion  Net movement of atoms or molecules from high concentration to low concentration is known as diffusion.   Rate of diffusion inversely proportional to the square root of the molecular weight of the gas, so that in air, oxygen, with a molecular weight of 32, diffuses 1.2 times faster than carbon dioxide, with a molecular weight of 44 . Due to its greater solubility, the permeability constant of carbon dioxide in the tissues is 36 times greater than that for oxygen

28. Ventilation Change in volume of tracheal system is known as ventilation Simple Diffusion – In smaller or less active Insects  Ventilation – Large and Active insects ex. Grasshopper  Ventilation done by Contraction of muscles in the abdomen and air is forced out of trachea. As muscles relax, abdomen springs back to normal volume and air is drawn in . Large Air sacs attached to Tracheal tubes increase the effectiveness of    this bellow like action.

29. Fluttering In some lepidoptera larvae , pupae and some coleoptera .  Carbon dioxide is not released continuous but produced in bursts followed by long interval in which very little carbon dioxide is liberated although uptake of Oxygen is continuous. Advantage : Save water by closing the spiracles

30. PNEUMATISATION The process of replacement of liquid by gas in the tracheal system is known as  PNEUMATISATION  Immediately after ecdysis the tracheal system will be filled with liquid after some time it replaced by gas is called PNEUMATISATION.

31. DISCONTINUOUS GAS EXCHANGE The movement of oxygen into the tracheae and carbon dioxide emission occur in discrete bursts when the spiracles open; relatively little gas exchange occurs while they are closed. This phenomenon is known as discontinuous gas exchange discontinuous ventilation.  It is common in adult insects when they are inactive at moderate to cool temperatures, that is, when their metabolic rates are low.   The pupae of many insects also exhibit DGE.

32. VARIATION IN GAS EXCHANGE

33. RESPIRATORY PIGMENTS Larval midges of the genus Chironomus Endoparasitic bot fly larvae in the genus Gastrophilus  have haemoglobins that enable them to extract oxygen from  extremely hypoxic media. 

34. Gaseous exchange in aquatic insects Aquatic insects obtaining oxygen directly from the air or from the dissolved oxygen in water. Oxygen from air Oxygen from water Insects subject to occasional submersion

35. A. Oxygen from air Insects make frequent visits to water surface for acquiring Oxygen . Prevent water entry into spiracles by  Possess hydrofuge properties around spiracles Production of oily secretion by perspirucular glands Hydrofuge properties around the spiracle are associated with hairs Some have  Semi Permanent connection with air {thus insect remain submerged ex. Larvae of Hoverfly, Eristalis (Diptera)} Thrusting Spiracle into Arenchyma of aquatic plants  Air Bubble

36. Hydrofuge properties around the spiracle are associated with hairs. When submerged ,hairs close over spiracle, preventing entry of water At surface , hairs separated by tension forces, spiracle exposed .  Ex. Notonecta ( Heteroptera )

37. Thrusting Spiracle into Arenchyma of aquatic plants . Ex. Chryogaster and Notophila (Diptera )  Semipermanent connection with the aerenchyma of a plant. The respiratory siphon of a mosquito larva ( Mansonia ) which connects with the aerenchyma of aquatic plants (after Keilin, 1944).  (a) Lateral view showing saw which cuts into the plant tissue and recurved teeth which hold the siphon in place. (b) Longitudinal section showing a terminal spiracle and a trachea.

38. Contact Angle   When a liquid rests on a solid or a solid dips into a liquid, the liquid–air interface meets the solid–air interface at a definite angle ; that is constant for the substances concerned.  This angle, measured in the liquid, is known as the contact angle .  A high contact angle indicates that the surface of the solid is only wetted with difficulty; such surfaces are said to be hydrofuge. 

39. Gas exchange via air bubbles Some insects carry a bubble of air down into the water when they dive. The spiracles open into this bubble, so that it provides a store of  additional air. The position of the store is characteristic for each species:    Ex. In Dytiscu s (Coleoptera), it is beneath the elytra  As oxygen is consumed, the bubble decreases in size.

40. . As the insect dives, the gases in the bubble are in equilibrium with those dissolved in the water.  As the insect uses oxygen, the equilibrium is perturbed. It is restored by the inward movement of oxygen and the outward movement of nitrogen. This is a continuous process; it is shown as two separate steps for clarity.  Note that carbon dioxide produced by the insect is immediately dissolved in the water. Oxygen comes out of solution faster than nitrogen goes in.  The bubble shrinks continuously as nitrogen goes into solution Diagram of an air bubble acting as a physical gill. 

41. B. Oxygen from water Closed Tracheal System: TRACHEAL GILLS : The immature stages of many aquatic insects lack a distinct communication with the exterior, the spiracle being closed or absent .  In such insects there is an extensive network of fine trachea beneath the integument, either concentrated in some regions or distributed all over as in tracheal gills of immature stages.       Lamellate gills/ Abdominal gills  - mayfly naiad     Filamentous gills - damselfly naiad      Rectal gills - dragonfly naiad 

42. Mayfly – Abdominal gills Rectal gills - dragonfly naiad  

43. Plastron respiration  Insects have specialized structures holding a permanent thin film of air on the outside of the body. This is known as Plastron.  Tracheae open into it so that oxygen can pass directly to the tissues. In adult insects the plastron is held by a very close hair pile in which the hairs resist wetting because of their hydrofuge properties and their orientation.  The most efficient resistance to wetting would be achieved by a system of hairs lying parallel with the surface of the body Ex.   Aphelocheirus Aphelocheirus

44. C. Insects subject to occasional submersion Spiracular gills : A spiracular gill is an extension of the cuticle surrounding a spiracle and bearing a plastron connected to the tracheal system by aeropyles . In water, the plastron provides a large gas–water interface for diffusion, while in air the interstices of the gill provide a direct route for the entry of oxygen, and water loss is limited because the gill opens into the atrium of the spiracle.  Thus, in air, water loss through the spiracles is scarcely greater than in terrestrial insects. 

45. Spiracular gills of a pharate adult cranefly ( Taphrophila )   . (a) Diagram showing basic structure and connection of gill to the tracheal system; the two left-hand branches represent the gill as seen from the outside; the remainder have the upper layer of cuticle removed to show the extent of the atrium.  (b) Transverse section through a gill branch. (c) Detail of a plastron line.

46. Gas exchange in endoparasitic insects Endoparasitic insects may obtain their oxygen directly from the air outside the host or by diffusion through the cuticle from the surrounding host tissues. Diptera depend entirely on cutaneous diffusion Braconid larvae the hindgut is everted through the anus to form a caudal vesicle.

47. Functions Of Respiratory System Provide the cells and tissues with oxygen.  To eliminate carbon dioxide a product of respiration.  It gives some degree of buoyancy in aquatic insects in phantom midge Chaoborus (Diptera).  Hemolymph circulation.  Act as connective tissues and binds the organs together.  Air sacs allow growth of the body.  Tracheal system involves In sound production in Gromphodorrhina ( Blattodea ) by forcing air through the spiracles.  Air sacs also helps as heat insulators and to maintain body temperature. Tracheoles involves in light emission in fire flies.

48. References  The Insects Structure and Function FIFTH EDITION R. F. CHAPMAN  Handbook of Entomology by T.V. Prasad  Insecta An Introduction  by K.N. Ragumoorthi  , V. Balasubramani, M.R. Srinivasan, N. Natarajan) ENTOMOLOGY REFRESHER by Viji C.P. K. Phani Kumar http://www.dynamicscience.com.au/tester/solutions1/biology/respiratory/insectresp.html https://acis.cals.arizona.edu/community-ipm/community-ipm-output/publications/publications-view/mosquitoes https://www.kqed.org/science/341205/natures-scuba-divers-how-beetles-breathe-underwater https://www.sciencephoto.com/media/367844/view/water-scorpion https://scrubmuncher.wordpress.com/2011/08/09/lift-off/ https://www.giand.it/diptera/morph/?id=48&lang=en https://www.freeexamacademy.com/movement-in-and-out-of-cells