This document discusses the excretory system in insects. It notes that the main excretory organs in insects are the Malpighian tubules and the alimentary canal (rectum). The Malpighian tubules arise from the gut and remove nitrogenous waste from the body. Their structure varies between species but generally has an absorptive proximal region and secretory distal region. Terrestrial insects excrete waste as uric acid or urates while aquatic insects excrete ammonia. Other excretory functions are carried out by the integument, nephrocytes, fat bodies, oenocytes, and tracheal system.

1. R.K. PANSE
Assistant Professor (Entomology)
College of Agriculture, Balaghat
Murjhad Farm Waraseoni
Email: rkpanseento@gmail.com
Mobile No. : 9806145992
Lecture no. 17
Structure and functions of excretory
system in insects

2. Excretion
Removal of waste products of metabolism, especially
nitrogenous compounds from the body of insects is known
as excretion. The excretion process helps the insect to
maintain salt water balance and thereby physiological
homeostasis.
Followings are the excretory organs in insect:
Main systems
Malpighian tubules (major system)
Alimentary canal (rectum)
Other systems
Integument
Nephrocytes
Fat bodies
Oenocytes
Tracheal system

3.  Malpighian tubules of insects are long tubular epithelium,
closed at one end, arise from the gut near the
junction of mid- and hindgut, and lie freely in the
body cavity, in most insects.
 Malpighian tubules are considered to be evaginations of
hindgut and hence are ectodermal in origin.
 Marcello Malpighi first described these in 1669.
 The number of Malpighian tubules in insects may vary,
from species to species
Spring tail and aphids absent
Scale insects 2
Bugs 4
Mosquitoes 5
Moths and butterflies 6
Cockroach 60
Locusts >200
Malpighian tubules

4. Malpighian tubule can be differentiated into two regions,
based on their histology and functions. The microvilli in the
lower (proximal) one-third absorptive region are more
widely spaced, forming a typical “brush border”, comprising
the cytoplasmic filaments of varying lengths (7-40μ long). In
the remaining two-third distal (upper) secretory region,
parallel and closely spaced microvilli (3-10μ) form a striated
“honey comb” border.
Structure of Malpighian tubules

5. Terrestrial insects excrete waste products as uric acid or certain
of its salts called urates, which were water insoluble and
requires less amount of water for waste product removal. In
aquatic insects ammonia is the excretory product, which is
freely soluble in water and requires more amount of water for
waste product removal.
Physiology of Nitrogenous excretion
Uric acid + carbonate or
bicarbonate= urate
Na + or K+ ions secret in to blood by
secretory region of MT
Urate + Na + or K = K+ urate
K+ urate absorbed by secretory
region of MT
K+ urate breaks in to K+ and urates
K+ absorb by absorptive region of
MT and urate excreted by rectum.

6. Basic nephridial system
Cryptonephridial system
Basic nephridial system: MT free into the blood cavity
Types of excretory systemsCryptonephy
Cryptonephridial system: The distal
ends of the Malpighian tubules
are held in contact with the rectal
wall. (e.g. Adult Coleptera, larval
Lepidoptera and larval
symphyta).

7. Functions of MT: Excretory in function, removal of
nitrogenous wastes. The other accessory functions are as:
1. Spittle secretion in spittle bug
2. Light production in Bolitophila
3. Silk production in larval neuroptera
Storage Excretion: The excretory waste materials are
retained within the body in different sites.
i. Uric acid is stored as urates in the cells of fat body e.g.,
American cockroach.
ii. Uric acid is stored in the body wall, giving white colour.
e.g. Red cotton bug.
iii. Uric acid is stored in the male accessory glands to
produce the outer coat of spermatophore.
iv. Uric acid is stored in the wing scales giving white colour.
e.g., Pierid butterflies.
v. Waste products of pupal metabolism (Meconium) is stored
and released during adult emergence.

8. •Nephrocytes: Cells that sieve the haemolmph for products
that they metabolize (pericardial cells).
Other excretory organs
•Integument: The outer covering of the living tissues of an
insect.
•Tracheal system: The insect gas exchange system,
comprising tracheae and tracheoles.

9. Fat bodies: A loose or compact aggregation of cells, mostly
trophocytes, suspended in the haemocoel, responsible for
storage and excretion
•Rectum: The posterior part of hind gut.

10. •Oenocytes: These are specialised cells of haemocoel,
epidermis or fat body with many functions. One of the
function is excretion.