Any chemical that can kill or repel a pest is a pesticide. In addition to various chemical pesticides various living organisms are utilized to destroy the undesirable organisms-they are known as biopesticides. Pesticides can also be classified on the basis of nature of organisms they control.
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Classification of pesticides :
Chemical Pesticides :
On the basis of their chemical nature pesticides are classified as follows :
1. Organochlorines : They are chlorinated hydrocarbons. The common example are DDT (Dichloro-diphenyl trichloro-ethane), BHC (Benzene hexachloride), Heptachlor, DDE, Chlordane,Lindane, Endosulphan, Aldrin, Dieldrin.
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DDT is the most famous pesticide of the world. BHC is sold under the name of Gammexane or Lindane and is most important pesticide.
Organochlorines decompose very slowly, hence they accumulate in the environment.
2. Organophosphates : Organic esters of phosphoric acid, thiophosphoric acid and other phosphoric acids, e.g ., Malathion, Parathion, Trithion, Ethion, TEPP (Tetraethyl pyrophosphate), Fenitrohion. Malathion is most widely used organophosphate and is important ingredient of ‘flit’.
Organophosphates work on central nervous system inhibiting its normal function resulting in convulsions, paralysis and death (this character led to the development of nerve gas used in world war II).
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3. Carbamates : Organic esters of carbonic acid e.g., Carbaryl, Carbafuran, Aldicarb, Propoxur. Methyl isocyanate gas which caused Bhopal gas tragedy in 1984 is used in manufacture of carbaryl.
4. Pyrethoids : They are synthetic derivatives of pyrethrin obtained from Chrysanthemum cinerarifolium.
5. Triazines : They are derived from urea e.g ., Simazines and Triazines. Pesticides inhibit metabolism of organisms. Retard photosystem II in plants.