Insect Mouthpart and its modifications

INSECT MOUTH PARTS AND ITS MODIFICATIONS

Mouth parts of insects vary to a great extent among insects of different groups depending upon their feeding habits. The basic categories are

a.    Madibulate mouth parts (feeding on solid food)

b.    Haustellate mouth parts (feeding on liquid food)

A typical insect mouthpart consists of,

§  Labrum (upper lip)

§  A pair of mandibles (primary jaw)

§  A pair of maxillae (secondary jaw)

§  Labium (lower lip)

§  Hypopharynx (Tongue)

Types of mouth parts

1. Biting and Chewing type:

      Eg: Cockroach, Beetles, Grasshoppers, Lepidopteran larva

a.    Labrum: A rectangular plate

b.    Mandible: First pair of jaws, which has sharp incisors or teeth and grinding organs

c.    Maxilla: Second pair of jaws comprising two lobes namely cardo and stripes which bears five segmented maxillary palpi. Stipes carries galea and lacinia

d.    Labium: Consists of prementum, mentum and submentum. Prementum bears a pair of paraglossa and a pair of glossa and bears a pair of three segmented labial palp

e.    Hypopharynx: A tongue like organ where the salivary gland opens through.

2. Piercing and Sucking type

a)    Hemipterous / Bug type. Eg. Plant bugs

It has four stylets.

ü  Labrum : short flap or hook that covers the groove in the labium at its base.

ü  Labium: three or four segmented proboscis/beak/rostrum which is grooved on one side and encloses the stylets.

ü  Mandible : a pair of stylet

ü  Maxillae: a pair of stylets; each maxilla is double grooved on its inner side & when   held together tightly they form two channels namely food channel and salivary     channel.

ü  Hypopharynx:  Small narrow some what elongated structure present at the base of stylets.

b)    Dipterous / Mosquito type. Eg. Female mosquito

 Six stylets are present in this type.

ü  Labrum: Modified as stylet and called labrum epipharynx. It forms the food channel along with hypopharynx.

ü  Mandible : A pair of stylets

ü  Maxillae: A pair of stylets, provided with small teeth like projection near the tip to make the punctures in the skin of the animals. It has a pair of maxillary palp.

ü  Labium: Elongate sheath bearing a pair of sensory lobe known as labella.

ü  Hypopharynx: a stylet. It is much elongated and is like double edged sword present immediately below the labrum epipharynx. It has the salivary duct.

            Mandibular and maxillary stylets together penetrate the skin. Saliva containing anticoagulant is injected through the salivary channel and the partially digested food is sucked through the food channel.

3. Chewing and Lapping type.

            Eg. Honey bees, Bumble bees.

ü  Labrum : semi circular lobe.

ü  Mandibles: spoon shaped or flattened.

ü  Maxillae: Lacinia absent or reduced. Galea is large and its inner surface is concave.

ü  Labium: Glossae are fused together to form an elongated structure known as glossal tongue. It bears a small sensory lobe known as flabellum. The glossal tongue is grooved ventrally and it works up and down. A pair of labial palps is well developed.

• First segment of labial palp is long. When the labial palps and galea are in contact wth each other in such a manner that they form a circle around the glossal tongue, thus enclosing the food channel. The food is drawn up in this channel by the movements of glossal tongue.    

• Hypopharynx : Absent.

4. Sponging type 

            Eg. House fly, Blow fly.

ü  Labrum: elbowed, whose base is rostrum and distal end is haustellum.

ü  Mandible : Absent

ü  Maxillae: Only the maxillary palps are visible.

ü  Hypopharynx: Forms food channel along with labrum epipharynx.

ü  Labium: Fleshy, elbowed and rectractile proboscis. The end of the labium has specialized large sponge like organ called labellum which has a series of furrows and channels called the pseudotracheae.

            Once the labellum is pressed on the liquid, the pseudotracheae fill with liquid by capillary attraction.

5. Siphoning type

            Eg . Butterflies & Moths

ü  Labrum: Reduced very much.

ü  Mandible: Absent

ü  Maxilla: Rudimentary, represented by maxillary palp. Galea is greately elongated and joined to form a slender hallow tube called proboscis.

ü  Labium: Small membranous area, labial palps are large, hairy, three segmented present on either side of proboscis.

ü  Hypopharynx : Absent.

The proboscis is kept under the head when not in use. Feeding of the nectar is aided by uncoiling the proboscis, projecting its tip into the liquid and sucking it up through the food channel, which runs through the proboscis.

6. Cutting and Sponging type

            Eg. Horse flies.

ü  Labrum: Forms the food channel

ü  Mandible: Sharp and blade like

ü  Maxilla: Long probing styles

ü  Labium:  Sponge like, which posses small parallel capillary channel

ü  Hypopharynx: Forms food channel along with labrum.

The mandibles and maxilla together cut and tear the skin of mammals resulting in flow of blood. The blood is sucked by the sponge like labium and pass through the channel formed by the hypopharynx and labrum epipharynx.

7. Rasping and Sucking type

      Eg: Thrips.

This type is intermediate between piercing-sucking type and chewing type.

ü  Labrum: Flap like

ü  Mandible: Right mandible is absent. So this type is called as asymmetrical mouth part. Left mandible present as stylet.

ü  Maxilla: Stylet

ü  Labium: Ventral sheath

ü  Hypopharynx: Stylet.

The labrum and hypopharynx together form the food channel, hypopharynx and labium form the salivary duct. The stylet lacerates the epidermis and the sap exuding from the wound is sucked up by the stylets.

8. Mandibulo- Suctorial type

            Eg. Grubs of ant lions and aphid lions

Also called grasping and sucking type

ü  Mandibles: Strong, long, slender, sickle shaped, provided with a groove or canal, for grasping and piercing the prey.

ü  Maxilla: Elongate, flattened, work together with the mandibles and form the food channel.

Miscellaneous types:

 

 9. Labial mask Ex: Dragonfly naiad

  

10.Mouth hook Ex: Fly maggot.