Chemicals are used not only to eradicate or control arthropod, but also as repelling and frightening agents. After the discovery of the insecticidal properties of DDT in 1939 by Paul Muller, the chemical control of insects has become most popular. The main reason for its popularity is the spectacular and immediate results obtained by the use of such chemicals. Hundreds of insecticides are now available to control different insect pests. These are used mainly as dust sprays or granules on the crops; dusts and granules can also be incorporated into the soil for the control of soil inhabiting insects.
The diverse chemicals used, as rodenticides are toxic to all animals and can generally be grouped into organic compounds, inorganic compounds, and organic fumigants. Of the organic compounds, the most popular are those that inhibit the coagulation of blood. These compounds interfere with the conversion of prothorombin to thrombin in the liver, and thus cause hemorrhages throughout the body by rupturing the capillaries. They eventually cause the animal to bleed to death internally. Another group of organic compounds sodium fluoroactate, and strychnine sulfate, an alkaloid, which causes animals to go into convulsions. Of the inorganic compounds, some of the more common ones in use are zinc phosphide, thallium sulfate, barium carbonate, yellow phosphorus, and white arsenic. Several fumigants are also used. These include carbon monoxide (combines with hemoglobin), methyl bromide (causes pulmonary congestion), and hydrogen cyanide (inactivates cytochrome oxidases). None of the compounds mentioned above are specific to any group of animals, and all are dangerous to humans. Chemicals are also used for frightening birds and mammals; these can be divided into lethal and nonlethal groups. The chemical agents pheny1 N-methyl carbamates (DRC-736) and4-amino-pyridine (DRC-1327) have shown promise for bird cntrol. Chemical repellents applied to the bark of dormant trees, conifer seedlings, an orchard trees have been successful for repelling rabbits, deer, and porcupines. Several chemicals, trinitrobenzene-aniline (TNBA), zinc dimethyldithiocarbamate cyclohexylamine (ZAC), and teramethyl thiuram disulphide (TMTD), have broad application for this purpose.
Less time is required and it gives quick control of pest.
Less amount of insecticide is required to control the pest population.
1. They are Nonspecific, thy must be used with precision to avoid killing of nontarget species.
2. Development of resistance where many target animals are developing genetic resistance to the widely used anticoragulant compounds.
3. Insecticide residues on crops and other products make them unfit for human consumption.
4. Excessive use of insecticides creates environmental pollution.