Abdominal Appendages

Abdominal appendages of insects can be grouped as

a) Pre-genital appendages

b) Genital appendages

c) Post genital appendages

A) Pre-genital appendages:

• Appendages before eight segments.
• It consists of the following:

I) Styliform appendages:

• In primitive pterygoids or ion-insect hexapods, there are pairs of small, unjointed styles each inserted on a basal sclerite called coxa along with eversible vesicles.

II) Collembolan appendages:

• On the third abdominal segment, a median lobe called a ventral tube project, and at its tip, long and tubular reversible vesicles are present in pairs.

III) Cornicles or siphunculi:

• Paired secretory structures located dorsally on the abdomen of aphids.
• The cornicles produce substances that repel predators or elicit negative behavior by symbiotic ants.

IV) Gills:

• Respiratory organs are found in the nymphs (naiads) of certain aquatic insects.
• In Ephemeroptera (mayflies), paired gills are located along the sides of each abdominal segment.
• In Odonata (damselflies), the gills are attached to the end of the abdomen.
• The gills have a direct role in gaseous exchange and more importantly to maintain a flow of water over the body.

V)Prolegs or pseudolegs:

• Except for the three pairs of thoracic legs,leg-likee outgrowths of the body wall in the abdominal region are the feature of many holometabolous insects and are called prolegpseudodo legs, or non-thoracic legs, or temporary legs.
• They are fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera).

Based on aseveralprolegs the larvae are categorized into the following types:

1) caterpillar: Larvae with 5 pairs of prolegs one pair each on 3-6 and 10 segments,

example: cabbage butterfly larvae

2) Pseudo caterpillar: The larvae with 6-9 pairs of legs one pair each on 2 to 7th and 10th segments, for example: sawfly

3) Loopers: Only two pairs one pair each on the 6th and 10th segments, for example: inchworm larvae.

4) Semiloopers: The larvae have three pairs of prolegs, for example, cabbage semi-loopers

B) Genital appendages

• The reproductive openings and genitalia are found on the ninth abdominal segment in males and on the eighth and ninth abdominal segments in females and are commonly called genital appendages.
• In females, paired appendages of the eighth and ninth abdominal segments fit together to form an egg-laying mechanism called the ovipositor.
• These appendages consist of four valves (basal sclerites with muscle attachments) and six valvulae (apical sclerites that guide the egg as it emerges from the female’s body).
• In males, the genital opening is usually enclosed in a tube-like aedeagus which enters the female’s body during copulation (like a penis).
• The external genitalia may also include other sclerites (e.g. subgenital plate, claspers, style, etc.) that facilitate mating or egg-laying.

C) Post genital appendages

• Cerci (singular cercus) are paired appendages on the rear-most segments of many Arthropoda, including insects and Symphyla.
• Many forms of cerci serve as sensory organs, but some serve as pinching weapons or as organs of copulation.
• They are rich in sensory cells and may be of importance in guiding copulation and oviposition.