Digestion System of Insects
An insect utilizes its digestive system to extract nutrients and other substances from the food it consumes.
- The majority of this food is consumed in the form of macromolecules and other intricate compounds (such as proteins, polysaccharides, fats, nucleic acids, and so on) which need to be broken down by catabolic reactions into smaller particles (i.e., amino acids, simple sugars, etc.) before being utilized by cells of the body for energy, growth, or reproduction.
- This break-down process is known as digestion.
- Insects may be phytophagous, entomophagous, wood borers, wool feeders saprophytic, mainly eating the solid food material which may be a plant part (or) tissue (or) wood, etc.
- Based on the food product ingested, there are structural modifications in the gastrointestinal system of insects.
- Insects feeding the solid food product have biting and chewing kind of mouthparts and well-established gizzards whereas sap-feeding insects have sucking-type mouthparts and have a filter chamber in the alimentary canal.
- The alimentary canal of insects is a long, muscular, and tubular structure extending from mouth to anus. It is separated into three areas viz., Foregut, Midgut, and Hindgut.
- 1) Foregut (Stomodaeum)
- 2) Mid Intestinal tract (mesenteron or stomach or ventriculus)
- 3) Hindgut (proctodaeum)
- 4) Digestion Glands
- 5) Microbes in digestion
- 6) MCQs about Digestive System in Insects
- 7) Frequently Asked Questions (FAQs) – Digestion System of Insects
- 8) Summary of Digestion System of Insects Tutorial
- 9) You may also like to learn:
Foregut (Stomodaeum)
The foregut is ectodermal in origin. Anterior invagination of ectoderm form foregut (Stomodeum). Internal cuticular lining exists. Terminal mouth parts lead into a preoral cavity. A preoral cavity in between the epipharynx and hypopharynx is called a Cibarium. Preoral cavity in between the hypopharynx and the salivary duct is Salivarium.
Behind the mouth, a well-musculated organ called Pharynx exists which presses the food into the esophagus. Pharynx functions as a suction pump in sap feeders. The esophagus is a narrow tube that performs food into the crop.
The crop is the dilated distal part of the esophagus functioning as a food tank. In bees’ crop is called as honey stomach where nectar conversion occurs. Proventriculus or Gizzard is the posterior part of the foregut and is musculated. It is discovered in solid feeders and missing in fluid feeders or sap feeders. The internal cuticle of the gizzard is variously modified as follows
- Teeth like in cockroach to grind and strain food.
- Plate like in honey bee to separate pollen grains from nectar.
iii. Spinal column like in flea to break the blood corpuscles.
Food circulation from foregut to midgut is managed through the Heart valve or Esophageal valve.
Mid Intestinal tract (mesenteron or stomach or ventriculus)
This area is likewise termed as stomach or midgut and its shape and capacity vary exceptionally. In many cases it is saclike, in others it is coiled and tubular like an intestinal tract or it may be divided into two or more regions.
Internally it is lined by a line of enteric epithelium the outer ends of whose cells rest upon a base membrane. This is followed by an inner layer of circular muscles and an external layer or longitudinal muscles. The outermost coat of the stomach is a thin peritoneal membrane.
In numerous insects, the surface area of the stomach is increased by the development of sac-like diverticula the enteric or gastric caeca. These organs are normally positioned at the esophageal end of the stomach and are very variable in number. It is the middle one 3rd part of the alimentary canal which extends from hepatic caecae or cardiac valve to Malpighian tubes or pyloric valve.
The anterior a lot of part of the midgut surrounds the stomodeal valve is called cardia. From the front end of the cardia, 8 little and tubular, finger-like blind processes project freely into the haemocoel. The internal lining of the wall of the midgut is an endodermal epithelium of columnar cells, raised into numerous little, villi like folds.
The epithelium is internally covered not by cuticle, however by a thin, transparent peritrophic membrane formed of chitin and proteins. The long, slender, and yellow-colored blind tubules called Malpighian tubules, complimentary into the haemocoel from the hind end of the midgut, although associated with the digestion system, these tubules are actually concerned about excretion.
Hindgut (proctodaeum)
The hindgut is ectodermal in origin and produced by the posterior invagination of the ectoderm. The internal cuticular lining is present, which is permeable to salts, ions, amino acids, and water. The main functions of the hindgut are the absorption of water, salt, and other useful compounds from the faeces and urine.
The hindgut is distinguished into 3 regions viz., ileum, colon, and anus. In the larva of scarabids and termites, the ileum is pouch-like for housing symbionts and acts as a fermentation chamber. The rectum consists of rectal pads assisting in the dehydration of faeces and it opens out through the rectum.
Digestion Glands
(a) Salivary glands
In Cockroach a pair of labial glands function as a salivary gland where the salivary ducts open into the salivarium. In caterpillars’ mandibular glands are customized to produce saliva, where the salivary glands are customized for silk production.
Functions of saliva
- (i) To moisten and to liquify food.
- (ii) To lubricate mouthparts.
- (iii) To add flavor to gustatory receptors.
(b) Hepatic caecae and midgut epithelial cells
It produces the majority of the digestive Juices. Two types of cells are associated with enzyme secretion.
(i) Holocrine: Epithelial cells break down in the process of enzyme secretion.
(ii) Merocrine: Enzyme secretion happens without cell break down.
Microbes in digestion
In the insect body, few cells are housing symbiotic microorganisms called mycetocyte. These mycetocytes aggregate to form an organ called mycetome.
- (i) Flagellate protozoa – It produces cellulase for cellulose food digestion in termites and wood cockroaches.
- (ii) Bacteria – It helps in wax digestion in the wax moth.
MCQs about Digestive System in Insects
1. What is the primary purpose of the digestive system in insects?
- a) Reproduction
- b) Locomotion
- c) Nutrient extraction
- d) Sensory perception
- Answer: c
2. Which of the following macromolecules need to be broken down during insect digestion?
- a) Minerals
- b) Vitamins
- c) Proteins
- d) Water
- Answer: c
3. What structural modifications occur in the gastrointestinal system of insects based on the ingested food product?
- a) Respiratory adaptations
- b) Circulatory modifications
- c) Nervous system changes
- d) Gastrointestinal alterations
- Answer: d
4. What is the origin of the foregut in insects?
- a) Mesodermal
- b) Endodermal
- c) Ectodermal
- d) Exodermal
- Answer: c
5. Which organ in the foregut is responsible for grinding and straining food in insects like cockroaches?
- a) Crop
- b) Pharynx
- c) Salivarium
- d) Gizzard
- Answer: d
6. In which part of the alimentary canal is the crop located?
- a) Foregut
- b) Midgut
- c) Hindgut
- d) Stomach
- Answer: a
7. What is the function of the proventriculus or gizzard in the foregut of insects?
- a) Honey conversion
- b) Blood corpuscle breaking
- c) Pollen grain separation
- d) Food tank function
- Answer: b
8. How is food circulation from the foregut to the midgut controlled?
- a) Pharynx contraction
- b) Heart valve
- c) Esophageal valve
- d) Salivarium action
- Answer: c
9. Which part of the alimentary canal is termed as the stomach or midgut in insects?
- a) Foregut
- b) Midgut
- c) Hindgut
- d) Stomach
- Answer: b
10. What is the purpose of the enteric or gastric caeca in the midgut of many insects?
- a) Oxygen absorption
- b) Nutrient storage
- c) Surface area increase
- d) Waste elimination
- Answer: c
11. What is the internal lining of the midgut made of?
- a) Chitin and proteins
- b) Cuticle
- c) Peritrophic membrane
- d) Circular muscles
- Answer: c
12. What are Malpighian tubules primarily concerned with?
- a) Nutrient absorption
- b) Oxygen transport
- c) Excretion
- d) Reproduction
- Answer: c
13. From which germ layer does the hindgut originate?
- a) Endoderm
- b) Ectoderm
- c) Mesoderm
- d) Exoderm
- Answer: b
14. What are the main functions of the hindgut in insects?
- a) Oxygen absorption
- b) Nutrient digestion
- c) Water and salt absorption
- d) Reproductive processes
- Answer: c
15. Which regions does the hindgut consist of?
- a) Ileum, colon, and anus
- b) Foregut, midgut, and hindgut
- c) Cardia, stomach, and rectum
- d) Crop, proventriculus, and Malpighian tubules
- Answer: a
16. What is the function of salivary glands in the digestion system of insects?
- a) Nutrient synthesis
- b) Enzyme secretion
- c) Oxygen production
- d) Waste elimination
- Answer: b
17. Which glands in caterpillars are specialized for saliva production and silk production?
- a) Labial glands
- b) Salivary glands
- c) Mandibular glands
- d) Hepatic caecae
- Answer: c
18. What is the role of saliva in insect digestion?
- a) Lubricate mouthparts
- b) Add flavor to food
- c) Moistening and liquefying food
- d) All of the above
- Answer: d
19. What is the primary function of hepatic caecae in digestion glands?
- a) Nutrient storage
- b) Waste elimination
- c) Enzyme secretion
- d) Oxygen absorption
- Answer: c
20. What are mycetocytes in the insect body primarily associated with?
- a) Nutrient absorption
- b) Oxygen production
- c) Symbiotic microorganisms
- d) Reproductive processes
- Answer: c
21. Which microorganism produces cellulase for cellulose digestion in termites and wood cockroaches?
- a) Bacteria
- b) Flagellate protozoa
- c) Viruses
- d) Fungi
- Answer: b
Frequently Asked Questions (FAQs) – Digestion System of Insects
1. What is the purpose of the digestive system in insects?
- Insects utilize their digestive system to extract nutrients and other substances from the food they consume, facilitating energy, growth, or reproduction.
2. How are insects classified based on their feeding habits?
- Insects can be classified as phytophagous, entomophagous, wood borers, wool feeders, or saprophytic, depending on the solid food material they primarily consume.
3. What are the structural modifications in the gastrointestinal system based on the ingested food product?
- Structural modifications in the gastrointestinal system of insects depend on whether they are solid feeders with biting and chewing mouthparts or sap feeders with sucking mouthparts and a filter chamber in the alimentary canal.
4. How is the alimentary canal of insects structured?
- The alimentary canal of insects is a long, muscular, and tubular structure separated into three areas: Foregut, Midgut, and Hindgut.
5. What is the origin of the foregut in insects?
- The foregut is ectodermal in origin, formed by the anterior invagination of ectoderm known as Stomodeum.
6. What are the functions of the pharynx in the foregut?
- The pharynx, a well-musculated organ, functions as a suction pump in sap feeders, pressing food into the esophagus.
7. What is the role of the proventriculus or gizzard in the foregut?
- The proventriculus or gizzard, located in the posterior part of the foregut, is musculated and plays a role in grinding and straining food.
8. How is food circulation from the foregut to the midgut controlled?
- Food circulation from the foregut to the midgut is managed through the Heart valve or Esophageal valve.
9. What is the midgut in insects, and how is it internally structured?
- The midgut, also known as the stomach, varies in shape and may be saclike, coiled and tubular, or divided into regions. It is internally lined by enteric epithelium and has circular and longitudinal muscles.
10. What is the function of the peritrophic membrane in the midgut? – The peritrophic membrane, made of chitin and proteins, covers the internal lining of the midgut and aids in digestion.
11. How is the hindgut classified and what are its main functions? – The hindgut is ectodermal in origin and is responsible for absorbing water, salt, and other useful compounds from the faeces and urine.
12. What are the regions of the hindgut, and what is the role of the rectum? – The hindgut consists of ileum, colon, and anus. The rectum contains rectal pads that assist in the dehydration of faeces.
13. How do salivary glands contribute to digestion in insects? – Salivary glands, such as labial glands in cockroaches, produce saliva to moisten and liquefy food, lubricate mouthparts, and add flavor to gustatory receptors.
14. What is the significance of hepatic caecae and midgut epithelial cells in digestion glands? – Hepatic caecae and midgut epithelial cells produce digestive juices, with two types of cells associated with enzyme secretion: holocrine and merocrine.
15. What are mycetocytes, and what microorganisms do they house? – Mycetocytes are cells in the insect body that house symbiotic microorganisms, forming an organ called mycetome. These microorganisms include flagellate protozoa for cellulose digestion and bacteria for wax digestion.
Summary of Digestion System of Insects Tutorial
The Digestion System of Insects tutorial provides a comprehensive overview of how insects extract nutrients from their food for energy, growth, and reproduction. The tutorial covers various aspects of the digestive system, including the foregut, mid intestinal tract, hindgut, digestion glands, and the role of microbes.
- Insect Digestive Process:
- Insects break down macromolecules and complex compounds into smaller particles through catabolic reactions in the digestive system.
- The process involves the conversion of proteins, polysaccharides, fats, and nucleic acids into amino acids, simple sugars, and other essential components.
- Classification based on Feeding Habits:
- Insects can be classified based on their feeding habits, such as phytophagous, entomophagous, wood borers, wool feeders, or saprophytic.
- Gastrointestinal Structural Modifications:
- The structure of the insect’s gastrointestinal system undergoes modifications based on the type of food ingested, including mouthpart adaptations and the presence or absence of a well-established gizzard.
- Alimentary Canal:
- The alimentary canal in insects is a long, muscular, and tubular structure divided into three main parts: foregut, midgut, and hindgut.
- Foregut:
- Originating from ectoderm, the foregut includes the cibarium, salivarium, pharynx, esophagus, crop, and gizzard. The gizzard’s internal cuticle is modified for specific functions.
- Mid Intestinal Tract:
- Also known as the stomach or midgut, it varies in shape and is internally lined with enteric epithelium, circular and longitudinal muscles, and a peritrophic membrane. Sac-like diverticula increase its surface area.
- Hindgut:
- Originating from ectoderm, the hindgut is responsible for absorbing water, salts, and useful compounds. It is divided into ileum, colon, and anus.
- Digestion Glands:
- Salivary glands, mandibular glands, and hepatic caecae contribute to enzyme secretion, saliva production, and the production of digestive juices.
- Microbes in Digestion:
- Mycetocytes house symbiotic microorganisms in the insect body. Flagellate protozoa assist in cellulose digestion, and bacteria aid in wax digestion.
This tutorial provides valuable insights into the intricate digestive processes of insects, highlighting the adaptations and structures that enable them to thrive in various ecological niches.