Insect digestive system details ppt easy. To understand

1. AEN 201 FUNDAMENTALS OF ENTOMOLOGY
(2+1)
Lec: No. Lecture title
8. Insect digestive system, modification,
digestive enzymes, physiology of digestion
Dr. V.G. Mathirajan, Ph.D.
Professor (Agrl.Entomology)
Department of Entomology
Dr. MSS Agricultural College and Research Institute
Eachangkottai ,Thanjavur

2. Digestive system
 Divided into three regions
 Foregut or stomodaeum
 Midgut or mesenteron or ventriculus
 Hindgut or proctodaeum

3. Digestive system
 Divided into three regions
 Foregut or stomodaeum
 Midgut or mesenteron or ventriculus
 Hindgut or proctodaeum

4. Anatomy of Digestive system

5. Gut
FOREGUT MIDGUT HINDGUT

6. Foregut (Stoemodium)
 Ectodermal origin
 Intima: Cuticular lining
 Mouth (pre-oral cavity) leads into
pharynx
 Pharynx leads immediately into a
narrow tube oesophagus
 Salivary apparatus consists of two
pairs of salivary glands and a pair of
salivary reservoirs (digestive gland)
 Distal end of oesophagus enlarges
into a large sac-like structure – crop-
useful to store food prior to digestion
 Posterior part of crop narrows down
to a small sac- gizzard or
proventriculus
 Inside gizzard, six chitinous cuticular
teeth -help in pulverizing food

7. Head
(Cross Section)

8. Foregut Preoral cavity and Pharynx
 Salivary glands
 Cibarium: Cavity between
epipharynx & hypopharynx
 Salivarium: Cavity between
hypopharynx and salivary
duct
 Pharynx: Well musculated
organ that pushes food into
oesophagous in solid feeders
 Pharynx acts as sucking
pump in sap feeders
Foregut - lateral view
Head- cross section

9. Pharyngeal pump
Lepidoptera Homoptera

10. Foregut Oesophagous, Crop & Proventriculus
 Oesophagous:
 A narrow tube that conducts food
into crop
 Crop:
 Sac-like at distal, acts as reservoir of
food
 modified as honey stomach in bees
and sucking stomach in sucking
insects
 Proventruclus or Gizzard:
 Musculated and hard
 Found in solid feeders
 Teeth-like in cockroach &
grasshopper to grind and strain food
 Plate-like in honeybee to separate
pollen grains from nectar
 Spine-like in flea to break blood
corpuscles
 Absent in blister beetles and
caterpillars

11. Crop
Lepidoptera and Diptera
have permanent sac
The capacity of crop in
honey pot ants -enarmous

12. Midgut (mesentron)
 Endodermal origin
 Intima- absent
 Site of digestion & assimilation
 Parts:
 Gastric caecum –digestive
gland- finger-like projections
at the junction of foregut and
midgut, -serve as enzyme
source for digestion
 Ventriculus
 Peritrophic membrane


13. Gastric caecae
 Also called as entric caecae
or hepatic caecae
 Finger-like outgrowth
 Increases functional area of
midgut
 Shelters symbiotic microbes


14. Midgut
Ventriculus (not lined with cuticle)
 Internal lining secreted by
epithelial cells:
Peritrophic membrane
 Present in solid feeder and
absent in liquid feeder
 Semi permeable
 Lubricate and facilitate food
movement
 Protect midgut epithelium
 Acts as barrier to microbes


15. Midgut Cross Section

16. Midgut
Malpighian Tubules:
 Mesodermal in origin
 At the joint between midgut
and hindgut
 Excretory in function-
eliminates nitrogenous
waste from insect blood

17. Midgut modification -Filter chamber
 Anterior and posterior midgut
regions-in close contact so that
water can be diverted directly to
hindgut without diluting contents
of midgut
 Potassium is actively secreted
into Malpighian tubules and
posterior midgut drawing water
from anterior
 Much of this fluid containing
dilute concentrations of amino
acids and sugars: HONEYDEW

18. Midgut modification -Filter chamber
 Anterior and posterior midgut
regions-in close contact so that
water can be diverted directly to
hindgut without diluting contents
of midgut
 Potassium is actively secreted
into Malpighian tubules and
posterior midgut drawing water
from anterior
 Much of this fluid containing
dilute concentrations of amino
acids and sugars: HONEYDEW

19. Hindgut (Proctodeum)
 Ectodermal in origin
 Pyloric valve between hindgut
and midgut
 Malpighian tubules attach
below valve
 Internal cuticular lining-
present-permeable to salts,
ions, amino acids and water
 Narrow Ileum, wider colon
and sac-like rectum

20. Physiology of Digestion
Process of digestion
Conversion of food into a form capable of
assimilation by blood
Providing nourishment by action of digestive
chemicals
Extra-intestinal digestion

21. Extra-intestinal digestion
 Digestives juices-
secreted from mouth
onto food before their
intake into alimentary
canal
 Portion of food digested
 e.g. predaceous
beetles and bugs

22. Intra-intestinal digestion
Steps:
 Salivary gland secret saliva-mixes with food
 Partial digestion and no absorption in crop
 Solid food -crushed and broken in gizzard
 Cells of mesentron or midgut secret digestive enzymes and do
absorption of nutrients
 Lipid absorption by midgut caecae
 Sugars and proteins absorption by microvilli of midgut
epithelium
 Salts and water absorption by proctodaeum or hindgut and
also partial digestion by microorganism

23. Roles
Salivary glands
Digestive enzymes

24. Salivary Gland
Glands:
 Labial glands in cockraoch
 Mandibular glands in
caterpillars
 Two –lie ventral to foregut-
varied size and shape
 Often described as acinar
(cluster of grapes)
 Saliva-secretary product-
clear product
Functions:
 Food solvent, lubricate mouthparts,
transport flavour to gustatory receptors
 Saliva contains:
 Anticoagulins in mosquitos
 Amylase to digest starch in cockroach
 Invertase to digest sucrose in honeybee
 Lipase and protease to digest lipids and
protein in leafhopper
 Toxins, which produces tissue necrosis and
phytotoxemia, by planthopper
 Pectinase in stylet penetration in plant bugs
 Pectinase for partial digestion by
predaceous insects
 Indole acetic acid produce galls by gall
insects
 Saliva useful in:
 Pathogens transmission by insect vectors
 Gluing of puparial cages to substrate in flies

25. Digestive Juices or Enzymes
Insect group Enzymes
Phytophagous larvae Amylase, Maltase,
Invertase
Omnivorous Protease, Lipase
Nectar feeders Invertase
Wood boring cerambycid grubs and
termites
Cellulase
Meat eating maggots Collagenase
Wool feeders (bird lice) Keratinase

26. Microbes in digestion
 Symbiotic microorganisms -called
MYCETOCYTE: protozoa, bacteria, fungi
 They aggregate to form an organ:
MYCETOME
 Microbes provide:
 Vitamins and amino acids in bed bugs &
cockroach
 Cellulase for cellulose digestion in wood
termites
 Bacterial enzymes to digest wax in wax
moth
 Microbes transmission:
 Mouth-to-mouth food exchange
(trophallaxis)


27. Absorption of nutrients
 In many insects absorption of nutrients occurs through
microvilli of midgut epithelial cells by diffusion
 Absorption of water and ions occur through rectum in
hind gut
 In cockroach, lipid absorption occurs through crop
 In termites and scarabaeids, absorption occurs through
ileum
 In solid feeders, re-absorption of water from faeces
occurs in rectum and faeces -expelled as pellets
 In sap feeders (liquid feeders)- faeces liquid like-
Liquid faeces of Homopteran bugs (aphids, mealy bugs,
scales and psyllids) with soluble sugars and amino
acids-Honey dew- which attracts ants for feeding