insect excretory system, malphigian tubules lecture igkv. first year first sem

1. AEN 201 FUNDAMENTALS OF ENTOMOLOGY (2+1)
LEC No. Title
9. Malpighian tubules - accessory excretory
organs and physiology of excretion

2. Insect Excretory system
• Process of elimination of harmful metabolic products
especially the nitrogenous compounds
• Excretion helps insects
– to maintain salt-water balance- physiological Homeostasis
(maintenance of constant internal environment)
• Accomplished by:
– Removal of nitrogenous waste
– Regulation of ionic composition of haemolymph

3. Excretion and Osmoregulation
 Insect excretory product faeces - either in liquid form or solid pellets
 Contains both undigested food and metabolic excretions
 Aquatic insects excrete dilute wastes from their anus directly into
water by flushing with water
 Terrestrial insects must conserve water
 Requires efficient waste disposal in a concentrated or dry form
 Simultaneously avoiding toxic effects of nitrogen

4.  Both terrestrial and aquatic insects must conserve ions, such as
sodium (Na+), potassium (K+) and chloride (Cl-) - limiting in their
food or lost into the water by diffusion.
 Therefore production of insect excreta (urine or pellets) is a result
of two related processes: excretion and osmoregulation
(maintenance of favourable osmotic pressure and ionic
concentration of body fluid)
 Excretion and osmoregulation is referred to as excretory system
and its activities are performed largely by the Malpighian tubules
and hindgut
 In fresh water insects, haemolymph composition is regulated in
response to loss of ions to the surrounding water, with the help of
excretory system and special cells.
 Special cells - called Chloride cells - present in the hindgut-
 Capable of absorbing inorganic ions from the dilute solutions
 (e.g. Naids of dragonflies and damselflies)

5. Excretory Organs
1. Malpighian Tubules
2. Nephrocytes
3. Fat Bodies
4. Oenocytes
5. Integument
6. Rectum

6. Malpighian tubules
• Italian anatomist, Marcello Malpighi, first discovered in 1969
• Main organ of excretion and osmoregulation -acting in
association with rectum or ileum
• Outgrowths of alimentary canal and consist of long, slender,
thin and blind-ending tubules
• Functional differentiation of tubules-with distal secretary region
and proximal absorptive region
• Open into intestine near junction of mid and hindgut and close
at their distal ends

8. Number of Malpighian Tubules
Spring tail, aphids – Absent
Scales – 2
Plant bugs – 4
Mosquitoes – 5
Moths and butterflies – 6
Cockroach – 60
Dragonflies, grasshopper, Locusts – 200

9. Variation in roles of Malpighian tubules
• Usually free in body cavity and bathed
in haemolymph
– Grasshoppers, crickets, mole
crickets and bugs
• Distal end of tubules- embedded in
tissues surrounding rectum-
“Cryptonephridial or Wider kidney”
condition
– Beetles, moths, butterflies, weevils
and wasps
– Condition enables insects to
conserve water by withdrawing
moisture from faeces

10. • In some blood feeders (Dipterans), distal region of tubules-
secretory in nature-Cells of internal wall of tubules closely
packed microvilli-condition is honeycomb border
• In proximal region- cells have more widely dispersed microvilli-
called brush border
• Primary function -excretion and regulation of internal
environment by controlling ion and water balance in blood and
by removing nitrogenous waste
• Other accessory functions
– Spittle secretion in spittle bug (Cercopids)
– Light production in Bolitophila
– Silk production in larval Neuroptera ( lace wing fly, ant lion)
Variation in roles of Malpighian tubules

11. Short term surpluses (Blood feeders)
Activation of tubule to increase activity
Ions pumped in, water follows

12. Cryptonephridial System
 Distal ends of Malpighian
tubules - held in contact with
rectal wall by perinephric
membrane
 Concerned either with efficient
dehydration of faeces before
their elimination or ionic
regulation
 (e.g. Adult Coleptera, larval
Lepidoptera and larval
Symphyta)

13. Nephrocytes
• Group of cells found in
localized regions that sieve
haemolymph for products after
metabolization
• Some present on surface of
insect heart – pericardial cells
• Clear foreign chemicals of high
molecular weight, which
Malpighian tubules- incapable
of excreting
• Accumulates and removes
Dye-stuff, ammonia, carmine

14. Fat Bodies
• A loose or compact aggregation of
cells, mostly Trophocytes suspend
in haemocoel –useful for storage
excretion
• Principal function –to synthesize
and storage of fat, protein &
glycogen
• Fat bodies contain special cells-
URATE cells-serve as special
storage & excretory cells of urates
• Storage products-eliminated at
the time of pupation

15. Oenocytes
• Large cells associated with
epidermis or fat bodies
• For many functions and
excretion in one of functions

16. Integument
• Outer covering of living tissues of an insect
• Moulting -a process of excretion- nitrogenous waste products
• Final products of metabolism - transferred to certain parts of
integument and stored- lost with exuviae in each moult

17. Rectum
Posterior part of hind gut

18. Physiology of Excretion

19. Physiology of Excretion
• Tubules in direct contact with
blood and produce a filtrate,
which produce isosmatic but
ionically dissimilar to
haemolymph
• Selectively absorbs water,
dissolved salts, amino acids and
nitrogenous waste and eliminate
others
• Isosmatic filtrate has high K+, low
Na+ with Cl- which pass down
into lumen of tubules by simple
diffusion/ active transport

20. Physiology of Excretion
• Sugars and amino acids-
passively filtered from
haemolymph via junctions
between MT
• Some other amino acids, hard
metabolites and toxic organics
-actively transported into MT
lumen
• Sugars- reabsorbed from
lumen and returned to
haemolymph
• Salts, water and nutritive
substances -condensed in
proximal part of tubules and
discharged into hindgut

21. Physiology of Excretion
• Reabsorbtion of water & salt takes
place in rectum with funtional
papillae, while nitrogenous waste
pass out with faeces
• In rectum –urine modified by removal
of solutes and water to maintain fluid
and ionic homeostasis
• During feeding insect may ingest
some potentially toxic substances
– Large molecules and colloidal
particles of toxic materials -
ingested and metabolized by
Nephrocytes
– Other smaller molecules may be
actively secreted by MT

23. Salt and water balance in insects
• Various environmental conditions pose
different salt and water problems in
insects
• Terrestrial insect face water loss through
transpiration and depend on ingested
food for water and salt
• Depending upon water content of diet,
faecal material may be
– Thin water -Honeydew -in sucking
insects that take in excess of water
– Dry powdery pellets- in insects that
feed on food with very low water
content

24. Constant surpluses (Plant feeders)
Cicadoidea
Xylem feeders
Filter chamber to handle
constant excess water

25. Filter chamber
Midgut is very long, with
distinct sections
Last section loops back and
forms complex with first +
Malpighian tubules

26. Nitrogen excretion, why ?
• Nitrogenous products accumulate in haemolymph as a
result of protein, amino acids and nucleic acid
metabolism
• Nitrogenous products-generally of no use and may be
toxic hence excreted as insect urine or stored as an inert
material until excreted
• Nitrogenous products or wastes
– Uric acid
– Ammonia
– Aallantoin
– Allantonic acid and
– Urea

27. Nitrogen Excretion
• Type of excretion in
terrestrial insects-
Uricotelism
Uric acid or its salt called
urate -major nitrogenous
waste product- water
insoluble -require less
amount of water for
removal
• Type of excretion in
aquatic insects-
Ammonicotelism
Ammonia – major
excretory product-water
soluble and requires
more water for removal

28. Storage excretion
• Excretory wastes- retained in body in a
harmless form instead of being passed
• Uric acid is stored:
– as urate cells in the fat bodies in
American cockroaches
– In body wall- gives white colour in red
cotton bug
– In male accessory glands to produce
outer coat of spermatophore- which
excreted during copulation
– In wing scales- which gives white
colour in Pieris
– as metabolic waste during pupal
period – meconium in Moths &
butterflies