Integrated Pest Management

Pests can be defined as any animals, plants, or microorganisms that interfere with some human purpose. For example, insects may be considered pests if they eat crop plants or stored foods, or if they are important vectors in the transmission of diseases of humans or domestic animals. Plants are considered to be pests, or weeds, if they excessively compete with crop plants in agriculture or forestry, or if they have an unwanted aesthetic, as is the case of weeds in grassy lawns. Microorganisms are regarded as pests if they cause diseases of humans, domestic animals, or agricultural plants. In all of these cases, humans may attempt to manage their pest problems through the use of pesticides, that is, chemicals that are toxic to the pest.

Very important benefits can be gained through the judicious use of pesticides. For example, agricultural yields can be increased, and stored foods can be protected. Human lives can also be saved by decreasing the frequency of diseases spread by arthropods; malaria, for example, is spread through bites of a few species of mosquitoes. However, there are also some important negative consequences of the use of pesticides to achieve these benefits.

Pesticides are toxic chemicals, and they are rarely specifically poisonous only to the pests against which they may be used. The spectrum of pesticide toxicity is usually quite wide, and includes a diverse range of non-pest (or nontarget) species, in addition to the pest. Most insecticides, for example, are poisonous to a wide range of insect species, to other arthropods such as spiders and crustaceans, and often to fish, amphibians, birds, and mammals, including humans.

Moreover, the operational use of pesticides does not usually achieve a specific exposure of only the pest target—a large number of nonpest species is also exposed. This includes nonpest species occurring on the actual spray site, as well as species elsewhere that are exposed through offsite drift or other movements of the sprayed pesticide. Nontarget exposures are especially important when pesticides are applied as a broadcast spray over a large treatment area, for example, by an aircraft or tractor-drawn apparatus.

Some important ecological effects are caused by the typically broad spectrum of toxicity of pesticides, and the extensive exposures to non-pest species whenever broadcast sprays are used. For example, the extensive spraying of synthetic insecticides to manage epidemic populations of spruce budworm (Choristoneura fumiferana), an important defoliator of conifer forests in northeastern North America, results in huge nontarget kills of diverse arthropod species, and deaths of birds and other vertebrate animals. Similarly, the use of herbicides kills large numbers of plants, in addition to the few species that are sufficiently abundant to be considered weeds.

In addition, some pesticides are toxic to humans, and people may be poisoned as a result of exposures occurring through the normal use of these chemicals. The most intense exposures involve accidents, and in rare cases people may be killed by pesticide poisoning. Usually, however, the exposure is much smaller, and the toxic response is milder, and often not easily measurable. Generally, people who are employed in the manufacturing or use of pesticides are subject to relatively intense exposures to these chemicals. However, all people are exposed to some degree, through the food, water, and air in their environments. In fact, there is now a universal contamination of animals, including humans, with certain types of pesticides, most notably the persistent chlorinated hydrocarbons, such as DDT.

Other ecological effects of pesticide use occur as a result of habitat changes. These effects are indirect, and they can negatively influence populations of wildlife even if they are not susceptible to direct toxicity from the pesticide. For example, the use of herbicides in forestry causes large changes in the abundance and species composition of the plant community. These changes are highly influential on the wildlife community, even if the herbicide is not very toxic to animals.

Obviously, it is highly desirable that alternative methods of pest management be discovered, so that our reliance on the extensive use of pesticides can be diminished.