Pest control

Pest control is the regulation or management of species defined as pests. A pest is any animal, plant, or fungus that adversely impacts human activities or the environment. People respond to these organisms based on the level of damage they cause. This response can range from simple tolerance to active management or deterrence. In some cases, humans attempt to completely eradicate a pest from a specific area.

In agriculture, farmers use several different strategies to manage pests. One method is cultural control, which involves changing farming habits to prevent pest build-up. For example, crop rotation helps by depriving pests of their specific host plants. This tactic has reduced the early season incidence of the Colorado potato beetle by as much as 95%. Another method is mechanical control, or tillage. This involves using tools like a plough to turn the soil. Tillage can expose pests, such as the larvae of the common click beetle, to predators like birds.

Biological control is a specialized method that uses other living organisms to manage pests. This relies on natural mechanisms like predation, parasitism, or herbivory. There are two main types of biological control. Classical biological control involves introducing natural enemies that were bred in a laboratory. An alternative is augmentation, where humans release more of the natural enemies already present in an area.

An example of this is using the bacterium Bacillus thuringiensis israelensis to infect and kill mosquito larvae in water.

Chemical pest control involves applying pesticides to crops. These substances include herbicides to kill weeds, fungicides to kill fungi, and insecticides to kill insects. Pesticides can be applied as sprays by hand, via tractors, or even by aircraft.

While effective, the efficacy of chemical pesticides often diminishes over time. This happens because organisms that survive the application pass on their genes to offspring. This process allows a resistant strain to develop, which requires farmers to use higher concentrations or more expensive formulations.

History shows that humans have managed pests for thousands of years. As early as 3000 BC in Egypt, cats were used to protect grain stores from rodents.

In China, around 4000 BC, ducks were used in paddy fields to consume pests. The Sumerians used sulphur compounds as insecticides around 2500 BC. By the 1880s, ladybirds were used in California to control scale insects. In the 20th century, the discovery of synthetic insecticides like DDT changed the field. However, the environmental damage caused by these chemicals led to a renaissance of biological control methods.

Modern science also uses genetics to achieve host-plant resistance. This means growing crops that have inheritable traits to resist pests. These plants might repel feeding, prevent colonization, or simply tolerate the presence of a pest without losing yield. Some resistance is achieved through genetic engineering, such as Bt corn or papaya that is resistant to the ringspot virus. This approach reduces the need for heavy pesticide use.

In urban environments, pests include rodents, birds, and insects that share habitats with humans. These organisms may spoil possessions or feed on human resources. Control in cities often involves exclusion, quarantine, repulsion, or physical removal.

In some cases, humans also use hunting or culling to manage populations. This targets animals known as vermin that might transmit pathogens or damage livestock. While hunting can change animal behavior, it is one of many tools used in the complex system of pest management.