INSECT DIGESTIVE SYSTEMS

Insect Digestive System

Developmentally

12

3

1. Foregut (stomatodeum) - ectodermal

2. Hindgut (proctodeum) - ectodermal

3. Midgut (mesenteron) - endodermal

cuticle

FOREGUT MIDGUT HINDGUT

pharynx

esophagus

crop

Malpighian tubulessalivary glands

cibarium

salivariumgastric caeca

proventriculus

pylorus

ileum

rectum

ventriculus

anus

Variation in insect guts

What does the digestive system do?

1. Obtaining food

2. Mechanically breaks good down into smaller particles that facilitate the activity of digestive enzymes.

3. Enzymatic breakdown of larger food molecules into molecules that can enter the hemolymph.

4. Produce molecules that coordinate feeding and other digestive activities

Salivary Glands

Salivary Glands

Two types

1. Acinous (alveolar) – multicellular with sac-like units-directly innervated from CNS

Subesophageal ganglion

Produces dopamine for fluid secretion

Stomatogastric NSProduces seratonin for enzyme production

2. Tubular – not directly innervated- seratonin from hemolymph to regulate enzyme production

Functions of Salivary Glands

1. Moisten food

2. Lubricate mouthparts

3. Contains digestive enzymes

3a. Amylase – complex sugars to simple sugars

3b. Salivary enzymes for preoral digestion

4. Non-digestive functions

4a. Toxins of predators that affect CNS of prey

4b. Counter toxins of plant allelochemicals

4c. Anti-coagulants

4d. Silk production

Insect Saliva - Composition

e.g. Mosquito saliva

- 20 polypeptides

> 70 unique proteins

Insect Saliva – Composition - changes

Prates et al, 2008. J. Med. Ent 45:409

Lutzomyia longipalpis

Insect Saliva – Composition - changes

Prates et al, 2008. J. Med. Ent 45:409

Lutzomyia longipalpis

Salivary Glands

Aphid Blood feeders

Silk cocoons Plant galls

Salivary glands are involved in disease transmission

ForegutCicada (Homoptera)

pharynx

esophagus

crop

Malpighian tubulessalivary glands

cibarium

salivariumgastric caeca

proventriculus

pylorus

ileum

rectum

ventriculus

anus

Foregut

Proventriculus -

intima

-grasshopper

Peritrophic membrane

Secretion

Delamination

••••••••••

••••

••• •

• • •• •••••

••

Peritrophic membrane

Membrane secreting cells

Invagination of stomatodeum

Secretion vesicles

Peritrophic membrane

Peritrophic membrane

Peritrophic membrane

Bacterium

Food

Peritrophic membrane

Peritrophic membrane

Peritrophic membrane

Enclosing fecal pellet

Peritrophic membrane

pharynx

esophagus

crop

Malpighian tubulessalivary glands

cibarium

salivariumgastric caeca

proventriculus

pylorus

ileum

rectum

ventriculus

anus

Midgut Enzymes -

Insect Diet Protease Lipase Amylase Invertase Maltase

Cockroach omnivorous √ √ √ √ √

Carausius phytophagous √ √ √ √ √

Lepidoptera larvae

phytophagous √ √ √ √ √

adults nectar √

adults Non-feeding

Lucilia meat √ √

Glossina blood √

Termites

Absorption of digested material

Absorption of digested material

Movement of H20

Movement of water, inorganic ions, sugars & amino acids

caecum

Malpighian tubule

Absorption of digested material

Cicadas

Fat Body

Cross section of mosquito abdomen (FB = fat body)

Fat Body

Functions of fat body

- metabolism of carbohydrates, lipids and nitrogenous compounds

- storage of glycogen, fat and protein

- regulation of blood sugar

-synthesis of major hemolymph (blood) proteins(haemoglobins, vitellogenins, storage proteins)

Fat Body

Functions of fat body – changes with needs – e.g. calliphorin

10

5

0

Am

ount

of

call

ipho

rin

in h

emog

lobi

n

~7

~3

~.03

Fat Body – cell types

Trophocytes-carry out most of functions of fat body

Urocytes- storage of urates/uric acid