The term ‘insecticide’, in a broad sense, includes substances used for the destruction of insects and related pests. For centuries, various kinds of plant materials have been used to combat insects, rats and other pests in different parts of the world. At present, over a thousand plants are known to have insecticidal properties, yet only a few are of any commercial value. Pyrethrum, derris, cubé and tobacco are the best known and most commonly used insecticides of vegetable origin. Even these better-known insecticides tend to be overshadowed by the development of synthetic insecticides, such as DDT (dichlorodiphenyl-trichloroethane), chlordane, aldrin, malathion, benzene hexachlorides and others.

Before the use of pesticides, the man was often totally at the mercy of insects that attacked either him or his crops. History abounds with records of pests and diseases of phenomenal magnitudes. Some diseases, such as late blight and wart of potatoes, black rust of wheat, downy and powdery mildew of grapes, coffee rust, Dutch elm disease, citrus tristeza and canker, white pine blister rust, curly top of sugar beets, chestnut blight, etc. have caused severe epiphytotic in various parts of the world. Since the earliest times, locusts have blighted crops. In the middle of the nineteenth century, a fungal pathogen, Phytophthora infestans (Mont.) de Bary almost destroyed the Irish potato crop on which the rural population subsisted.

The Irish famine and locust plagues could not have occurred if pesticides had been known. Pesticides have proved valuable in combating diseases, such as malaria, yellow fever, sleeping sickness, the plague and many others.

A host of chemicals (such as colloidal sulphur; arsenical compounds; fluorides and other fluorine salts; various formates, butyrates, propionate, palmitate, stearate; dinitro compounds of cresol and phenol; various phenothiazones and phenothiazene and a number of cyanide containing compounds) have been used in the past to control insect pests. The discovery of DDT (first of the organochlorine pesticides to have a general use) and its subsequent introduction in controlling insect pests, however, came as a great boon to the mankind. Large amounts of DDT have been used since the early forties because of its remarkable power as an insect killer. It quickly became a universal weapon in agriculture and public health campaigns against disease carriers. By December 1969, there were more than 900 different active pesticides available in more than 60 000 preparations.