Fundamentals of Entomology

IDENTIFICATION

• All insects present in the world are not yet identified and described (about 25% of the insect species are unidentified). An already described species produce new race which requires further identification. Identification helps to understand about the organism and to take proper control measure. Insects can be identified through an expert, by comparing the available collections, using photographs and pictures and by using taxonomic keys.
• Key is a tabular statement presenting alternatives, describing about the features of an organism. Most of the keys are dichotomous i.e., always dividing into two or they are always in the form of couplets and give a clear cut alternative. Keys can be constructed based on single character (monothetic key) or many characters (polythetic key). Polythetic key is more advantageous.
• Monothetic key has three disadvantages
  (i) the organism may be an exception for a particular character
  (ii) chances of erring is more
  (iii) if the particular body part is broken on which the key is made, then the key cannot be used.
• Key can be classified based on evolutionary principles also as phylogenetic key and arbitrary key
  (i) Phylogenetic key: The key is based on the evolutionary relationship. The group appears only once in the phylogenetic key.
  (ii) Arbitrary key : The taxa or group appears at several places in the key. It has more advantages.