Piercing and Sucking Type of Mouth Parts (e.g. Red Cotton Bug)
There are two distinct operations are involved in this type of mouth parts (i) piercing and (ii) sucking. The insects having such type of mouth parts are different plant bugs, aphids, jassids, whiteflies, mealy bugs, scale insects etc. they feed on liquid food material like plant cell sap. The principal parts, which are modified to form piercing and sucking mechanism in red cotton bug, are as follows
1. Labium: It is a long, four-segmented beak like hollow structure called as rostrum or proboscis. This enclosed 4 needle like structures called as stylets, in the dorsal groove. Labium, does not take part in piercing the tissue and sucking the cell sap.
2. Mandibular and Maxillary Stylets: Lying inside the dorsal groove of the labium, are four, very sharp chitinous stylets, which are responsible for piercing the plant tissues and sucking up the cell sap.
The outer pair constitutes the Mandibular stylets which are usually serrated at the apex. The inner pair constitutes the maxillary stylets, which tapers to a fine point. Each maxillary stylet is double grooved along its inner face. When such two stylets fit tightly against each other two microscopic closed types are formed. The dorsal tube is the suctorial tuber while the ventral food channel and communicates with cibarial sucking pump. The ventral tube is ejection channel or salivary channel for ejecting the saliva. Maxillary palps are absent. Each Mandibular and maxillary stylets alternately have downward and upward movement for the purpose of piercing due to retractor and protractor muscles arising from the respective Mandibular and maxillary plates. All the four stylets normally cling together appearing like a single bristle. All the four stylets pierce the tissues.
1. Labrum:
Labrum is a short, triangular, flap like structure, which covers the labial beak at its base.
2. Hypopharynx: is highly specialized greater protion of it forms the floor of cibarial sucking pump which is provided with strong dilator muscles arising from the clypeus.
Feeding Mechanism: At rest, proboscis is always held parallel to the ventral side of the insect body. When insect is about to feed, the proboscis is stretched and stylets are released out from the labial groove. Then the proboscis gets looped behind so as to allow the stylets to penetrate in to plant tissues.
The Mandibular stylets pushing first followed by the maxillary stylets, alternately and it rapid rate, thrust themselves into the epidermis till they reach the cell sap. Saliva is then poured into the plant tissues from the salivary glands by means of salivary channel. This saliva also acts as lubricant in between the sliding Mandibular and maxillary stylets. The cell sap is then sucked by means of suction canal into the mouth cavity by the action of cibarial pump. The cibarial muscles are powerful, which when contract, a vacuum is created in the mouth cavity and cell sap slowly rises up through the food channel because of capillary movement and passes into the oesophagus after the relaxation of dilator muscles.