The document discusses the excretory system of insects. It begins by defining excretion as the removal of metabolic waste from cells, while defecation is the passing of undigested food. Aquatic insects excrete directly into water, while terrestrial insects conserve water by producing concentrated waste. The main organs of excretion are the Malpighian tubules and hindgut. The Malpighian tubules filter waste from the hemolymph and produce primary urine. The hindgut, especially the rectum, then selectively reabsorbs water and ions while eliminating other wastes like nitrogenous compounds in the form of uric acid. This allows for efficient water conservation in terrestrial insects.

1. Kingdom of Saudi Arabia
Al Imam Mohammad Ibn Saud Islamic University
College of Science
Department of Biology
Entomology
353 Bio
T. Amani Alsharidah
1441 – 2019

2. Lecture 11
Insect Excretory System

3. Introduction
The excretion:
 The removal from the body of waste products of metabolism, especially
nitrogenous compounds.
 It differs from defecation In that excretory wastes have been metabolized in cells
of the body.
The Defecation:
 Simply passing of waste directly from the mouth to the anus.
 Insect feces, either in liquid form or packaged in pellets and known as frass,
contain both undigested food and metabolic excretions.

4. Aquatic insect
 Eliminate dilute wastes from their
anus directly into water.
 in aquatic insects, lost ion into the
water by diffusion.
Terrestrial insect
 Must conserve water. This requires
efficient waste disposal in a
concentrated or even dry.
 both terrestrial and aquatic insects must conserve ions, such as sodium
(Na+), potassium (K+), and chloride (Cl−), that may be limiting in their food.
So the Production of insect urine or frass. therefore results from two intimately
related processes: excretion and osmoregulation.
Osmoregulation is the maintenance of a favorable body fluid composition
(osmotic and ionic homeostasis)

5. The Excretory System
 The system responsible for excretion and osmoregulation is referred to
loosely as the excretory system.
 Its activities are performed largely by the Malpighian tubules and hindgut.
 In freshwater insects, hemolymph composition must be regulated in response
to constant loss of salts (as ions) to the surrounding water, and ionic
regulation involves both the typical excretory system and special cells, called
chloride cells.
 Chloride cells usually are associated with hind gut which are capable of
absorbing inorganic ions from very dilute solutions.

6. The Malpighian tubules and rectum
 The main organs of excretion and osmoregulation in insects are the Malpighian
tubules acting in concert with the rectum and/or ileum.
 Malpighian tubules are outgrowths of the alimentary canal and consist of long thin
tubules formed of a single layer of cells surrounding a blind-ending lumen.
 They range in number from as few as two in most scale insects (coccoids) to over
200 in large locusts.
 Generally they are free, waving around in the hemolymph, where they filter out
solutes.
 Insect Malpighian tubules are considered to belong to the hindgut and be
ectodermal in origin.
 Their position marks the junction of the midgut and the cuticle-lined hindgut.

7. The Malpighian tubules and rectum
excretory process ( nitrogen excretion)
 The anterior hindgut is called the ileum, the generally narrower middle portion is
the colon, and the expanded posterior section is the rectum.
 In many terrestrial insects the rectum is the only site of water and solute
resorption from the excreta.
 Insects ingest nitrogen, particularly certain amino acids far in excess of
requirements ,Most insects excrete nitrogenous metabolic wastes at some or all
stages of their life, although some nitrogen is stored in the fat body or as proteins
in the hemolymph in some insects.
 Many aquatic insects excrete large amounts of ammonia.
 Terrestrial insects wastes generally consist of uric acid combination with urea,
pteridines, certain amino acids, and/or relatives of uric acid, such as hypoxanthine,
allantoin, and allantoic acid.
 Amongst these waste compounds, ammonia is relatively toxic and usually must be
excreted as a dilute solution

8. Cont.
 Urea is less toxic but more soluble, requiring much water for its elimination.
 Uric acid are non-toxic and, having low solubility in water. (at least in acidic
conditions), can be excreted essentially dry, without causing osmotic problems.
 Waste dilution can be achieved easily by aquatic insects, but water
conservation is essential for terrestrial insects and uric acid excretion
(uricotelism) is highly advantageous.

9. The Malpighian tubules and rectum

10. The Malpighian tubules and the hind gut
 The Malpighian tubules
produce a filtrate (th
primary urine) which is
isosmotic but ionically
dissimilar to the
hemolymph.
 And then the hindgut,
especially the rectum,
selectively reabsorbs
water and certain
solutes but eliminates
others.
Excretory process