General Organization of an Insect Body
The body of an insect is covered with a hard chitinous cuticle (exoskeleton) which project, it from mechanical injury and prevent excessive loss of moisture. The body is segmented i.e. composed of series of successive rings, called segments.
Metameres/Somites: Where these are movable, they are separated by flexible inter-segmental membranes. The body is divided into three distinct regions viz., the head, thorax and abdomen.
Head: The head consist of six embryonic segments. The head is concerned with feeding and sensory perception. It bears a pair of antennae, a pair of compound eyes, three ocelli and the mouth parts. Head is highly sclerotized. The sclerotized capsule manus the appendages is called cranium.
Compound eyes are located at dorso-lateral sides of the head. Each eye consists of a number of separate visual elements called ommatidia. Compound eyes are useful in image perception ocelli are situated in between the compound eyes. There simple eyes. They are sensitive to light intensity but not useful in image perception. Antennae are paired segmental appendages that articulate with the cranium between the compound eyes. Antennae are flexible and are sensory in function. Mouthparts consist of labrum (upper lip), labium (lower lip), mandibles and maxillae (two pairs of jaws) and hypopharynx (tongue like organ).
Head is connected to thorax by a membranous region called the neck or Cervix. The cervical membrane is quite flexible and allows movement of the head.
Thorax: Thorax consists of three segments, viz., pro, meso and metathorax. Each segment consists of a dorsal region called the tergum (notum), ventral region called the sternum and lateral region pleuron on each side of body. Each thoracic segment bears a pair of segmented legs. The meso and metathorax each bears a pair of wing which are collectively called as pterothorax. Mesothoracic wing are called forewings and metathoracic wings are called hind wings. Thorax is mainly concerned with locomotion.
Abdomen: The abdomen consists of eleven segments, although it is difficult to distinguish all of them due to telescopic arrangements of the segments. The successive segments are joined by inter-segmental membrane called conjunctiva which makes the abdomen flexible, which is required during copulation and oviposition. Each abdominal segment usually composed of a dorsal (tergum) and ventral (sternum) plants, there is no pleuron. The tergum is connected to the sternum by a thin membrane. Posterior abdominal segments are modified for the purpose of mating and oviposition. The triangular dorsal plate of eleventh segment is call epiproct and paired lateral plates are called paraprocts. A pair of short unsegmented cerci is present between the epiproct and paraprocts. They are sensory in function. Anal openi9ngs are found immediately below the epiproct.
An oval shaped transparent auditory membrane, tympanum is found laterally on either side of the first abdominal segment e.g. grasshopper. There are eight pairs of openings called spiracles present on lateral sides of thoracic and abdominal segments, which are concerned with respiration.