• Abdomen forms the posterior part of the insect body. It is third and last tagma of insect body.
• This tagma is made up to 9-11 segments. It is highly flexible with more evident segmentation (uromeres).
• Upper sclerite is known as tergum. In thoracic segment tergum is known as notum.
• Lower sclerite is known as sternum.
• Side sclerite is known as pleuron.
• 8th and 9th are known as genital segments as they form genital appendages i.e., ovipositor in females and aedeagus or penis in males.
• The 8th and 9th segment in females and 9th segment in males have genital appendages which acts as external organ of reproduction. These segments are known as genital segments.
• Usually, 8 pairs of small lateral openings (spiracles) are present on the first eight abdominal segments.
• In grasshoppers, a pair of tympanum is found one on either side of the first abdominal segment. It is auditory organ. It is obliquely placed and connected to the metathoracic ganglia through auditory nerve.

Modification of Abdomen

• Reduction in number of abdominal segments has taken place in many insects.
• In spring tail only six segments are present. (S for six)
• In house fly only segments 2 to 5 are visible and segments 6 to 9 are telescoped within others.

  

• In ants, bees, and wasps, the first abdominal segment is fused with the metathorax and is called propodeum. Often the second segment forms a narrow petiole. The rest of the abdomen is called gaster.

  

• In queen termite after mating the abdomen becomes gradually swollen due to the enlargement of ovaries. The abdomen becomes bloated and as a result sclerites are eventually isolated as small islands. Obesity of abdomen of queen termite is called physogastry.

  

Abdominal appendages

Styli (Stylus: Singular)

• Varying number of paired tube-like out growths are found on the ventral side of the abdomen of silverfish. These are reduced abdominal legs which help in locomotion.

Anal styli

• A pair of short, unsegmented structure found at the end of the abdomen of male cockroach. They are used to hold the female during copulation.

  

Tracheal gills

• Gills are lateral outgrowths of body wall which are richly supplied with trachea to obtain oxygen from water in naiads (aquatic immature stages of hemimetabolous insects).
• Seven pairs of filamentous gills are present in the first seven abdominal segments of naiads of may fly and are called as lateral gills.

  

• Three or two leaf gills (lamellate) are found at the end of abdomen of naiad of damselfy and are called as caudal gills.

Prolegs

• Prolegs are unsegmented, thick and fleshy leg like structure present in the larvae of moth, butterfly and sawfly.
• Two to five pairs are normally present.
• The tip of the proleg is called planta upon which are borne heavily sclerotised hooks called crochets. They aid in crawling and clinging to surface.

  

Cerci (Cercus - Singular)

• They are the most conspicuous appendages associated normally with the 11th abdominal segment. They are sensory in function.

• They exhibit wide diversity and form.

• Long and many segmented: e.g., Mayfly

  

• Long and unsegmented: e.g., Cricket

  

• Short and many segmented: e.g., Cockroach

  

• Short and unsegmented: e.g., Grasshopper

  

• Sclerotised and forceps like: e.g., Earwig.

  

Ovipositor

• The egg laying organ found in female insect is called ovipositor.
• It is suited to lay eggs in precise microhabitats.

  

- Insecta - Introduction: K.N. Ragumoorithi, V. Balasurbramani & N. Natarajan
- A General Textbook of Entomology (9th edition, 1960) – A.D. Imms (Revised by Professor O.W. Richards and R.G. Davies). Butler & Tanner Ltd., Frome and London.
- The Insects- Structure and Function (4th Edition, 1998) – R.F. Chapman. Cambridge University Press
- Wikipedia