EXCRETORY SYSTEM OF INSECTS

• For the efficient maintenance of water and the ionic balance in the haemolymph, the waste products of the metabolism are to be removed or eliminated. These waste material may be in solid, semisolid, liquid or gaseous form.
• The principal excretory product in gaseous form is CO2, liquid form is honey dew, solid form is urea/uric acid and semi-solid form is allantoin.

The organs that are involved in the process of excretion are:

1. Malpighian tubules
2. Integument or body wall
3. Tracheal system
4. Alimentary canal
5. Nephrocytes

1. Malpighian tubules:

• The Malpighian tubules are long, tubular structures which open proximally in between midgut and hindgut and closed distally, floating freely in the haemolymph.
• Malpighian tubules are absent in aphids and Collembola.

Functions of Malpighian tubules:

a)Helps in the process of excretion or removal of waste products.

b)Regulate the internal body environment by maintaining ionic and water balance

c)In case of glow worms, the distal ends of tubules produces light energy.

d) Also helps in the storage of Ca necessary for the processes such as hardening of puparium.

2. Integument:

• In some insects, where respiration occurs through body wall, CO2 is removed through integument as waste product (cutaneous respiration).

3. Tracheal system:

• Function in elimination of CO2 through spiracles.

4. Alimentary canal :

• Removes the unwanted material, dead cells formed during enzyme secretion (holocrine) and intima layer during moulting.

5. Nephrocytes:

• Nephrocytes are cells that take up foreign chemicals of relatively high molecular weight which Malpighian tubules may be incapable of dealing with.
• Nephrocytes helps in the removal of ammonia, chlorides, dyes, colloidal particles etc.