Insecticides are substances which kill insects. Pesticides are used for the control of pests. Pesticide is a general term which includes insecticides, fungicides, herbicides and insect repellents.
Classification of insecticides
Insecticides are classified into:
1. Contact poisons : DDT, BHC, dihedron, pyrethrum
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2. Stomach poisons : Sodium fluoride, Paris green
3. Fumigants Sculpture dioxide Contact poisons kill the insects by direct contact. Stomach poisons kill the insects when ingested by them. Fumigants give off vapor which kill the insects.
DDT (Dichloride-biphenyl trichloroethane):
DDT is a white amorphous powder. It is insoluble in water but soluble in organic solvents. It is a good insecticide and acts as a contact poison. It kills many insects like lice, fleas, ticks and bugs. It enters the body of insects through their cuticle. It acts on the nervous system of insects and produces paralysis and death. It is used as a spray or aerosol. DDT is relatively safe to human beings and it is free from toxic effects.
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It is benzene hex chloride or hexachlorocyclo hexane. It is also called as gamelan or hex idol. It is a white or chocolate coloured powder. It has a musty smell and it is irritant to eyes, nose
and skin. It is a potent insecticide than DDT but the msecticidal action is less prolonged.
It kills insects by direct contact. It is used as a spray or as an aerosol like DDT.
Pyrethrum
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It is an insecticide obtained from the flowers of a plant called Chrysanthemum cinerariafolium. The flowers contains four nerve poisons. They are: 1. Pyrethrum I 2. Pyrethrum II 3. Cinerama I 4. Cindering II.
The flowers are extracted with kerosene. The kerosene extract (pyrethrum extract) is used as a spray for killing mosquitoes and other insects. Pyrethrum is a contact poison.