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insect cellular micro-organisms and their roles


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extra and intra cellular micro-organisms and their role in insect physiology

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insect cellular micro-organisms and their roles

  3. 3. INTRODUCTION The insects are rather uniform in their nutritional requirements (Dadd , 1985) but remarkably diverse in their diets (Slansky & Rodriguez 1987). There are insect predators, herbivores, generalist ‘scavengers’ and an array of specialists that utilize, for example, nectar, pollen, plant sap, fungi, fur, feathers, skin and blood. The capacity of some insects to adopt certain nutritional lifestyles cannot be attributed to traits of the insect alone but to an alliance between the insect and microorganisms with different biosynthetic or degradative capabilities from the insect. The basis for this nutritional ecology of many insects can be understood only by including microorganisms as an integral part of the ecological and physiological processes. Microorganism related to insect with relation is divided into in a two ways, (1) Casual associations (2) Constant associations 3
  4. 4. CASUAL ASSOCIATIONS  Micro-organisms are almost inevitably ingested during feeding and so an intestinal flora is present in most insects.  The alimentary canal of grasshopper , for instance , is sterile when the insects hatch from the eggs but soon acquires a bacterial flora, which increases in number and species throught life.  In general insects with straight alimentary canals contain fewer micro-organisms than those with complicated guts with a range of pH ,providing a number of different niches. 4
  5. 5.  These Casual Association with microorganisms are important in the nutrition of some insects.  Scarabaeoid larvae have a fermentation chamber in the hindgut in which decaying woods with its content of microorganisms is retained.  The microorganisms continue to ferment the wood and without them the larvae is unable to utilize the cellulose of the wood.  Microorganisms also assists with wax digestion in galleria although the insect can survive without them. 5
  6. 6. CONSTANT ASSOCIATIONS In General, constant association with microorganisms occur in insects with a restricted diet deficient in certain essential nutrients, suggesting that the microorganisms make good these deficiencies. thus microorganisms found in insects feeding on woods, dry cereals, feather, hair and wool, in sap feeding which at the some stage partake of other food do not house microorganisms. 6
  7. 7.  Thus symbionants are found in blood sucking bugs and lice ,and glossina and Nycteribidae, which are viviparous, among Diptera , but not in Fleas, blood sucking Nematocera or Tabanidae ,since these have free living larvae. (wigglesworth, 1952)  Microorganisms also found in cockroaches and some ants. These are omnivorous insects and hence in this instance the presence of microorganisms is not correlated with a restricted diet. 7
  8. 8. TYPES OF MICRO-ORGANISMS  The most commonly occuring microorganisms in insects are Bacteria or Bacterium like forms which are found in Blattodea, Homoptera, Heteroptera, Anoplura, Mallophaga, Coleoptera, Hymenoptera, and Diptera.  In additional flagellates (protozoa) are found in wood eating cockroaches and termites, yeast in Homoptera and Coleoptera and a Actinomycetes in Rhodnius. in many cases precise nature of the microorganisms is unknown. 8
  10. 10. LOCATION IN THE INSECT BODY In some insects the symbionants are free in the gut lumens.  This is the case with the flagellates which live in the hindguts of wood eating cockroaches and termites and with the bacteria living in the gastric caeca of the last segment of the midgut in plant sucking Heteroptera. In Rhodnius Actinomycetes lives in crypts between the cells of the anterior midgut. 10
  11. 11. Most microorganisms are intracellular in various parts of the body. The cell housing symbionants are known as mycetocytes and these my be aggregates together to form organs known as mycetomes. Mycetomes originates in the gut walls, as in Anoplura and Glossina, where the mycetome is a ring of enlarged midgut cells, or in modified malpighian tubules, as in some Coleoptera but frequently they are independent of the gut. 11
  12. 12.  In Calandra (coleoptera) larvae the mycetome is a U- shaped structure well supplied with tracheae lying below the foregut, but not connected to it (musgrave, 1964).  The wood eating cockroaches have two sets of symbionants; Intestinal-flagellates and intra-cellular bacteriods in the fat bodies. this situation also occur in termites Mastotermes darwiniensis, but the remaining of the wood eating termites only retain the intestinal fauna. 12
  13. 13. THE ROLE OF MICRO-ORGANISMS IN INSECT PHYSIOLOGY 1.BACTERIA Digestion and nutrition  In insects the digestion of food by gut associated bacteria has been demonstrated in crickets and cockroaches. The protozoan population is enriched when the cockroaches are exposed to a cellulose rich diet .  Similarly, it has been established that gut bacteria are responsible for the nitrogen metabolism of insect host and these microbes fix atmospheric nitrogen in fruit flies and termites.  These results amply support the view that bacteria associate with insects in providing essential nutrients, as against bacterial pathogens which depend on the insect/animal for its nutrient supply(R.Rajgopal, 2009). 13
  14. 14. Insects belonging to the order Hemiptera like aphids, white fly, mealy bug, plant hoppers feed exclusively on the plant sap a freely available sugar rich diet.  Since plant sap is very poor in nitrogen and amino acids, these insects have developed obligate symbiosis with bacteria like Buchenra (aphid) or Portiera (white fly), where in the bacteria supply all the essential amino acids required by the insect. While the insect accommodate these bacteria in specialized structures in their gut - mycetomes / bacteriocytes. 14
  15. 15. IMMUNITY AND PROTECTION Gut is a very dynamic environment, providing plenty of opportunity for the bacteria to flourish, thus resulting in extreme competition among bacteria to utilize the nutrients and survive within it. Many of the gut commensal bacteria have evolved to inhabit this environmental niche and thus are able to colonize the gut. In doing so, they provide effective protection against invasion by pathogenic microbes a process called colonization resistance (CR). 15
  16. 16. Axenic (germ-free) locusts were found to be extremely susceptible to infection by entomopathogenic fungus – Beauvaria and Metarhizium. Certain phenolic components having antifungal activity were absent in germfree locust and introduction of one of the gut bacteria – Pantoea agglomerans resulted in the appearance of a part of the phenolic repository. A similar effect on CR against Serratia marsceans was also observed Similarly, axenic silkworm (Bombyx mori) larvae were found to be more susceptible to Serratia piscatorum and baculo virus infection(Rajgopal,2009). 16
  17. 17. REPRODUCTION  Some microorganisms associated with insects have been implicated in altering the population ecology of their hosts.  The most studied of these are the Wolbachia, a common and widespread group of bacteria found in insect reproductive tissue.  These bacteria are protect against cytoplasmically inherited rickettsia that cause a number of reproductive alterations in their host, including cytoplasmic incompatibility between strains, parthenogenesis induction (Werren, 1997).  Wolbachia have additionally been shown to increase fecundity of insects (Vavre et al. 1999), and the nature of their effects vary with strain, arthropod species, and host genetic system (Johanowicz and Hoy 1998). 17
  18. 18. OTHER ROLE OF BACTERIA Other role of gut microorganisms are potential in the detoxification of food. Certain sources of nutrients are available only if toxins can be neutralized, and hydrolysis of some molecules.  Such as some plant cell wall components can both detoxify them and make them available as sources of nutrition. Many insects specialize on toxic plants or overcome chemicals used for insect control, and gut bacteria might serve as a portal for acquiring capabilities to digest and detoxify local food sources. 18
  19. 19. 2. PROTOZOA  Termites are consuming dead plants at any level of decomposition. They also play a vital role in the ecosystem by recycling waste material such as dead wood, faeces and plants.  Many species eat cellulose, having a specialised midgut that breaks down the fibre.  Termites having primarily symbiotic protozoa (metamonads) and other microbes. in their guts to digest the cellulose for them, allowing them to absorb the end products for their own use.  Gut protozoa, such as Trichonympha, in turn, rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. 19
  20. 20. 3. YEAST AND ACTINOMYCETES  The yeast of Stegobium (Coleoptera) provide B-Vitamins and sterols , which may be secreted into the guts, or release by the digestion of the microorganisms.  The symbionants of Bllatella provide certain amino acids and possibly a tripeptide as well as B-vitamins .blood is normally sterile and contains some of the B-vitamins in smaller amounts. than are required by insects.  In Rhodnius Actinomycetes lives in crypts between the cells of the anterior midgut, which are associated with bacteria in symbionants and help in the synthesis of some nutrients in guts. 20
  21. 21.  There is some evidence that the microorganisms, particularly those in Homoptera and Heteroptera ,are concerned with nitrogen metabolism (Toth, 1952).  This may result from the fixation of free nitrogen or by the breakdown of the insects metabolic waste products ,urea ,uric acids. into nitrogenous compounds that can be used.  Although it seems certain that the organism can perform these functions in vitro ,there is no proof that they do so when inside the host insects. 21
  22. 22. REFERENCES • CHAPMAN, R.F. The insect structure and function 95-88 • Philipp Engel & Nancy A. Moran, The gut microbiota of insects – diversity in structure and function, Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA • B. A. FREDERICK* and A. J. CAESAR, Analysis of Bacterial Communities Associated with Insect Biological Control Agents using Molecular Techniques : USDA/ARS Northern Plains Agricultural Research Laboratory, 1500 N. Central Ave., Sidney, Montana 59270, USA • Angela E. Douglas, Symbiotic microorganisms: untapped resources for insect pest control ; Department of Biology, University of York, PO Box 373, York, UK, YO10 5YW • C. Chellaram, S. Venkatesh, Antimicrobial Properties of Insect Gut Associated Bacteria. M.G.R. University, Chennai • R. Rajagopal, Benefi cial interactions between insects and gut bacteria. Indian J Microbiol (June 2009) 49:114–119 22
  23. 23. • LIPKE, H. and FRAENKEL, G. (1956). Insect nutrition A. Rev. entomology 377-389 • MUSGRAVE, A.J.(1964) Insect mycetomes Canadian entomology 96:377-389 • RICHARDS, A.G.(1972) and BROOK,M.A.(1958) Insect and mite nutrition north holland pub. Company. • SANG, J. H.(1959) Circumstances affecting the nutritional requirements of drosophilla melanogaster acd. Sci. 77:352- 356 • TOTH, L. (1952) the role of nitrogen –active microorganisms in the nitrogen metabolism of insect ent.95:43-62 • WALDBAEUR, G.P. (1956) The consumption and utilization of food by insects Adv. insect physio.6:271-290 • WIGGLESWORTH, V.B.(1952) Symbiosis in blood sucking insects. Ento.95: 63-69 23
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