Insecticide is a substance that kills insects. People use insecticides to control insect damage to crops, livestock, and buildings. People also use insecticides to control indoor pests and to combat diseases spread by insects.
Most insecticides are used in agriculture and forestry to protect plants. Without insecticides, insects would damage certain crops so much that farmers could not make profits. Many livestock owners spray their livestock with insecticide or dip them in an insecticide solution to protect them from flies, lice, mites, and ticks. People also use insecticides in homes to kill fleas, cockroaches, and other nuisance insects. Malaria, a deadly disease spread by mosquitoes, can be controlled by spraying insecticide where mosquitoes breed and on mosquito nets.
Most insecticides work as stomach poisons, contact poisons, or both. Stomach poisons kill insects that eat them. Contact poisons kill insects that touch them. Systemics are insecticides that are absorbed into the bodies of plants or livestock. When an insect bites the treated plant or animal, the insect ingests the insecticide and later dies. Fumigant insecticides form gases that kill insects. Chemosterilants, also called insect growth regulators (IGR’s), make insects unable to reproduce or otherwise change their normal life cycles to control their population. Many insecticides act in more than one way. Because insecticides can harm people and the environment, they are heavily regulated.
Types of insecticides
Insecticides are usually classified according to how they are made. The four main kinds are (1) inorganic insecticides, (2) synthetic organic insecticides, (3) botanical insecticides, and (4) microbial insecticides.
Inorganic insecticides
are usually made from minerals, such as sulfur, arsenates, fluorides, and mercury compounds. They were among the first kind people used. Many such inorganic insecticides were not as safe or as effective as other insecticides. Thus their use has been greatly limited or replaced. But some types, such as boric acid, remain in use.
Synthetic organic insecticides
are the most widely used type. They are artificially created substances consisting mainly of carbon, hydrogen, and oxygen atoms. Hundreds of synthetic organic insecticides are available. The word organic refers to the carbon-based nature of these compounds.
Three main types of synthetic organic insecticides, listed here, were widely used from the 1940’s through the 1970’s. Many have since been largely replaced by safer or more effective kinds. But some of them are still in use.
Chlorinated hydrocarbon insecticides,
sometimes called organochlorines, contain chlorine atoms. They are used to control a variety of insects that affect plants and animals. Chlorinated hydrocarbon insecticides include DDT, chlordane, lindane, and methoxychlor. These substances are persistent (long-lasting). They can accumulate in the bodies of larger animals. Once used, they can affect an area’s living things—including birds, fish, and other animals—for several years. Such insecticides have been blamed for widespread environmental damage and pose health risks. As a result, they have been replaced in many countries by safer insecticides.
Organophosphate insecticides
contain phosphorus atoms. They include diazinon, parathion, and malathion. They are less persistent than organochlorines. However, they typically destroy beneficial insects as well as harmful ones. Many are also poisonous to people. On the other hand, some are relatively safe. Malathion, for example, is still widely used.
Carbamate insecticides
contain one or more amino groups, which are made up of one nitrogen atom and two hydrogen atoms. Like organophosphates, many carbamates destroy both beneficial and harmful insects. They can become concentrated in the seeds and fruits of plants. Some concentrated carbamates cause harm to warm-blooded animals—including humans—who eat the plants. Many have thus been phased out of use.
Botanical insecticides
are derived from plants. Nicotine, pyrethrum, and rotenone come from various plants. They have been used to help control certain insect pests. Nicotine, from the tobacco plant, is a toxic poison that affects many kinds of insects. Pyrethrum, from a kind of flower, quickly kills many insects. But, like some other insecticides, it may cause mite populations to increase. Rotenone is extracted from several plants. It is poisonous to most fish, and so its use must be limited around bodies of water. Synthetic insecticides similar to pyrethrum and nicotine have grown in use since the late 1970’s and throughout the early 2000’s.
Microbial insecticides
spread diseases that infect insects. Many such diseases are caused by bacteria or fungi. Some rely on nematodes (roundworms) that grow inside insects and eventually kill them. Many microbial insecticides only affect specific insect types. As a result, they can destroy pests without causing wider harm. Some types of microbial insecticides do not use the actual organism that causes the disease. Instead, they use toxins (poisons) produced by the disease organism.
Using insecticides
Insecticides are applied in several ways, including dusting, spraying, fumigation, injection into plants, and mixing with irrigation water or insect bait. The use of insecticides is heavily regulated in an effort to prevent poisoning people and the environment.
Applying insecticides.
Some insecticides are mixed with powdered clay to form a fine dust. The dust can then be dropped over crops. However, dusts can easily drift to unintended areas. As a result, they are rarely used today.
Some insecticide dusts are mixed with water. The water evaporates after application, leaving a layer of dust. Insecticides may also be mixed with an oil or solvent and an emulsifier. The emulsifier binds the substances together. When mixed with water to dilute them, such insecticides form a creamy, white liquid. Such liquid-based insecticides can be dangerous to mix. They are thus often distributed premixed.
Other insecticides are injected directly into plants or animals. But only a few chemicals are suitable for such application. Injection also requires training to perform properly.
Dangers of insecticides.
Insecticides may be inappropriately applied or overused, causing environmental harm or even poisoning human beings. Insects may also develop resistance to certain insecticides, rendering the insecticides ineffective.
Insecticide producers are typically required to include label directions for mixing and application. The labels note what kind of personal protection equipment (PPE) people applying insecticide must wear. They also note how much time must pass before the area of application is safe for people and for harvesting crops.
