Structure of Insect Head PDF

Subject: Fundamental of Entomology Class: Ist yr, II Sem Teacher: Dr Yogesh Patel Asstt. Prof, College of Agriculture, Ganj Basoda STRUCTURE OF INSECT HEAD Insect head is a Anterior most part of insect body it is hard and highly sclerotized compact structure which consist...

Subject: Fundamental of Entomology Class: Ist yr, II Sem Teacher: Dr Yogesh Patel Asstt. Prof, College of Agriculture, Ganj Basoda STRUCTURE OF INSECT HEAD Insect head is a Anterior most part of insect body it is hard and highly sclerotized compact structure which consisting of six segments that are fused to form a head capsule. The insect head consists of mouthparts, compound eyes, simple eyes (ocelli) and a single pair of antennae. The head segments can be divided in to two regions i.e. procephalon and gnathocephalon (mouth). Insect head formed by the fusion of six segments that can be divided in to two regions i.e. procephalon and gnathocephalon (mouth parts). Six segments of head are represented as. Segment Appendages I Pre antennary segment No appendages II Antennary segment Antennae III Intercalary segment No appendages IV Mandibular segment Mandibles V First maxillary segment Maxillae VI Second maxillary / labial segment Labium  TYPES OF INSECT HEADS Based on the inclination of long axis of the head and orientation of mouth parts there are three types of insect heads. (a) Hypognathous (Hypo – Below: Gnathous – Jaw ) The head remain vertical and is at right angle to the long axis of the body and mouth parts are ventrally placed and projected downwards. This is also kwown as Orthopteroid type.. Eg: Grass hopper, Cockroach (b) Prognathous : (Pro – infront: Gnathous – Jaw ) The head remains in the same axis to body and mouth parts are projected forward.. This is also kwown as Coleopteroid type..Eg: beetles (c) Opisthognathous : (Opistho – behind: Gnathous – Jaw ) It is same as prognathous but mouthparts are directed back ward and held in between the fore legs..This is also kwown as Hemipteroid or Opisthorhynchous.. Eg: bugs Sclerites and Sutures of Head The head capsule is formed by the union of number of sclerites or cuticular plates or areas which are joined together by means of cuticular lines or ridges known as Sutures. These sutures provide mechanical support to the cranial wall. Frontal View of Insect Head  Lateral View of Insect Head Sclerites of Head A general insect posses the following sclerites. 1. Labrum : It is small sclerite that forms the upper lip of the mouth cavity. It is freely attached or suspended from the lower margin of the clypeus. 2. Clypeus: It is situated above the labrum and is divided in to anterior ante- clypeus and posterior post-clypeus. 3. Frons : It is the facial part of the insect consisting of median ocellus. 4. Vertex : It is the top portion of the head behind the frons or the area between the two compound eyes. 5. Epicraniun : It is the upper part of the head extending from vertex to occipital suture. 6. Occiput : It is an inverted “U” shaped structure representing the area between the epicranium and post occiput.  7. Post occiput : It is the extreme posterior part of the insect head that remains before the neck region. 8. Gena : It is the area extending from below the compound eyes to just above the mandibles. 9. Occular sclerites : These are cuticular ring like structures present around each compound eye. 10. Antennal sclerites : These form the basis for the antennae and present around the scape which are well developed in Plecoptera (stone flies). All the above sclerites gets attached through cuticular ridges or sutures to provide the attachment for the muscles inside. Sutures of Head The common sutures present in head are 1) Clypeolabral suture : It is the suture present between clypeus and labrum. It remains in the lower margin of the clypeus from which the labrum hangs down. 2) Clypeofrontal suture or epistomal suture: The suture present between clypeus and frons. 3) Epicranial suture: It is an inverted ‘Y’ shaped suture distributed above the facial region extending up to the epicranial part of the head. It consists of two arms called frontal suture occupying the frons and stem called as coronal suture. This epicranial suture is also known as line of weakness or ecdysial suture because the exuvial membrane splits along this suture during the process of ecdysis. 4) Occipital suture: It is ‘U’ shaped or horseshoe shaped suture between epicranium and occiput. 5) Post occipital suture: It is the only real suture in insect head. Posterior end of the head is marked by the post occipital suture to which the sclerites are attached. As this suture separates the head from the neck, hence named as real suture. 6) Genal suture: It is the sutures present on the lateral side of the head i.e. gena. 7) Occular suture: It is circular suture present around each compound eye. 8) Antennal suture: It is a marginal depressed ring around the antennal socket.