digestive system of an insects.pptx free

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1. Digestive system of Insects

2. Digestive system of Insects An insect uses its digestive system to extract nutrients and other substances from the food it consumes.   Most of this food is ingested in the form of macromolecules and other complex substances (such as proteins, polysaccharides, fats, nucleic acids, etc.) which must be broken down by catabolic reactions into smaller molecules (i.e. amino acids, simple sugars, etc.) before being used by cells of the body for energy, growth, or reproduction.   This break-down process is known as digestion.

3. All insects have a complete digestive system.   This means that food processing occurs within a tube-like enclosure, the alimentary canal, running lengthwise through the body from mouth to anus.  Ingested food usually travels in only one direction.  

4. Alimentary canal The alimentary canal of insects is a long, muscular, and tubular structure extending from mouth to anus. It is differentiated into three regions viz., Foregut, Midgut Hindgut. FOREGUT MIDGUT HINDGUT

5. Digestive system pharynx esophagus crop Malpighian tubules salivary glands cibarium salivarium gastric caeca proventriculus pylorus ileum rectum ventriculus anus

6. Foregut Foregut is ectodermal in origin. Anterior invagination of ectoderm forms foregut ( Stomodeum ). Internal cuticular lining is present. Terminal mouth parts leads into a preoralcavity . Preoralcavity between epipharynx and hypopharynx is called as Cibarium . Preoralcavity between hypopharynx and salivary duct is Salivarium . Food flow from foregut to midgut is regulated through Cardiac valve or Oesophageal valve.

7. Behind the mouth a well musculated organ called Pharynx is present which pushes the food into oesophagous . Pharynx acts as a sucking pump in sap feeders. Oesophagous is a narrow tube which conducts food into crop. Crop is the dilated distal part of oesophagus acting as food reservoir. In bees crop is called as honey stomach where nectar conversion occurs. Proventriculus or Gizzard is the posterior part of foregut and is musculated . It is found in solid feeders and absent in fluid feeders or sap feeders. Foregut

8. Midgut Midgut is endodermal in origin and also called as mesentron . This part contains no cuticular lining. Midgut is made up of three types of epithelial cells. ( i ) Secretory cells (Columnar cells) (ii) Goblet cells (aged secretory cells), (iii) Regenerative cells which replaces secretory cells.

9. ( i ) Peritrophic membrane It is the internal lining of midgut , secreted by anterior or entire layer of midgut epithelial cells. Present in solid feeders and absent in sap feeders. This layer is semi-permeable in nature to digestive juices and digestion products. Its functions are (a) Lubricate and facilitate food movement (b) Envelops the food and protects the midgut epithelial cells against harder food particles. Midgut

10. Midgut (ii) Gastric caecae : (Enteric caecae or Hepatic caecae ) Finger like outgrowths found in anterior or posterior ends of midgut . This structure increases the functional area of midgut and shelter symbiotic bacteria in some insects.

11. Midgut (iii) Pyloric valve: ( Proctodeal valve) Midgut opens into hindgut through pyloric valve, which regulate food flow. In certain immature stages of insects midgut is not connected to hindgut till pupation. e.g. Honey bee grub.

12. Midgut (iv) Filter chamber: Filter chamber is a complex organ in which two ends of ventriculus and the begining of hind gut are enclosed in a sac. This is useful to short circuit excess water found in liquid food in homopteran insects. This process avoids dilution of digestive enzymes and concentrates food for efficient digestion. Also helps in osmoregulation by preventing dilution of haemolymph

13. Hindgut Hindgut is ectodermal in origin and produced by the posterior invagination of ectoderm. Internal cuticular lining is present, which is permeable to salts, ions, aminoacids and water. The main functions of hindgut are the absorption of water, salt and other useful substances from the faeces and urine.

14. Hindgut Hindgut is differentiated into three regions : ileum, colon and rectum. In the larva of termites, illeum is pouch like for housing symbionts and acts as fermentation chamber. Rectum contains rectal pads helping in dehydration of faeces and it opens out through anus

15. How Pesticides enter the Insect’s Digestive System

16. These pesticides are designed to be ingested by the insect. They are typically formulated as liquids, dusts, pastes, granules, or baits. When insects consume these substances, the pesticides are absorbed into their digestive system. I nsects that chew on plant leaves such as grasshoppers, crickets, ants, cockroaches and earwigs. 1. Stomach Poisons

17. 2. Contact with Food Insects may come into contact with pesticides on their food sources, such as plants, fruits, or vegetables. When they consume these contaminated foods, the pesticides enter their digestive system.

18. Some pesticides are systemic, meaning they are absorbed by plants and translocated throughout the plant's vascular system. When insects feed on these treated plants, they ingest the pesticide along with the plant's sap. I nsects that suck sap from plants such as mealybugs, scale insects, aphids, true bugs and whiteflies. 3. Systemic Insecticides

19. Pesticides effect on Insect Digestive System

20. 1. Direct Toxicity Some pesticides directly damage the lining of the gut, leading to inflammation, ulceration, and impaired digestion. This can prevent insects from absorbing nutrients properly, weakening them and making them more susceptible to other stressors.

21. Many pesticides interfere with the activity of digestive enzymes, which are essential for breaking down food into usable nutrients. This can lead to malnutrition and reduced growth . 2. Disruption of Enzyme Activity

22. Some pesticides can disrupt the absorption of specific nutrients, such as amino acids or vitamins, leading to deficiencies and developmental problems. 3. Impaired Nutrient Absorption

23. The gut microbiota plays a crucial role in insect digestion, immunity, and overall health. Pesticides can disrupt the balance of these beneficial microbes, leading to dysbiosis and increased susceptibility to pathogens. 4. Alteration of Gut Microbiota

24. Dysbiosis is an imbalance in bacterial composition, changes in bacterial metabolic activities, or changes in bacterial distribution within the gut. The three types of dysbiosis are: 1) Loss of beneficial bacteria, 2) Overgrowth of potentially pathogenic bacteria, and 3) Loss of overall bacterial diversity.

25. References: Jaffar et al. (2024). Contribution of insect gut microbiota and their associated enzymes in insect physiology and biodegradation of pesticides. Contribution of insect gut microbiota and their associated enzymes in insect physiology and biodegradation of pesticides https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9516005/?need_sec_link=1&sec_link_scene=im Siddiqui et al. (2024). Role of Insect Gut Microbiota in Pesticide Degradation: A Review https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9111541/?need_sec_link=1&sec_link_scene=im Rouze et al. (2024). The Honeybee Gut Microbiota Is Altered after Chronic Exposure to Different Families of Insecticides and Infection by Nosema ceranae https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6759349/?need_sec_link=1&sec_link_scene=im