Insects attack plants in all stages of growth. They damage stored products. They also cause heavy losses to wooden structure. Insects are also responsible for the spread of serious diseases. A chemical substance used to kill insects is called an ‘insecticide’. There are various types of insecticides:

(a) Inorganic Insecticides- These include Paris Green, Calcium Arsenate, Lead Arsenate, Sodium Fluoride, Calcium Cyanide and a number of others.
(b) Insecticides of a Plant Origin- These include Pyrethrum, Rotenone and Nicotine.
(c) Synthetic Organic Insecticides- The most common is DDT.