What is a pesticide?
 A pesticide is a chemical intended to kill, or disrupt the population of, a pest organism. Pests are unwanted insects, mites, plants, disease causing organisms (antibiotics are technically pesticides), and other organisms that interfere with health or commerce. Insecticides target insects, herbicides target plants, fungicides target disease-causing fungi, and so on.
The definition of what is, or is not, a pesticide has nothing to do with whether or not the chemical is "organic" or natural. For example nicotine, a natural component of the tobacco plant, has been used as a powerful insecticide for more than a hundred years. Sulfur is an effective miticide and sodium borate, which is mined as "borax", is an effective insecticide. Pyrethrum from the dried flowers of certain species of chrysanthemum has been used as an "insect powder" for hundreds of years.
Synthetic pesticides have been around since shortly after World War II but until the mid-1990s there were only four categories:
- Organochlorine insecticides like aldrin, heptachlor, chlordane and DDT were developed to combat mosquitoes and lice and were later widely used, and mis-used, for other pests.
- Organophosphate insecticides like dimethoate, acephate (Orthene) and chlorpyrifos (Dursban) are far more acutely toxic to vertebrate animals but much less persistent in the environment than organochlorines.
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Silent Spring by Rachel Carson. This 1962 book started the movement to examine the impact of pesticides on the environment and eventually led to establishment of the Environmental Protection Agency in the US. (more information)
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In the last ten years there has been rapid development of new classes of insecticides with an emphasis on lower vertebrate toxicity and more targeted applications. Newer materials also tend to be much higher cost which has the benefit of reducing overall use.
In 1962 Rachel Carson published Silent Spring (above), a warning about the effects that the widespread use of highly persistent pesticides were having on the environment and wildlife. The book ignited a debate that eventually lead to the establishment of the Environmental Protection Agency (EPA) in the US during the early 1970s. Government oversight of pesticide use through label laws has directly lead to safer and less environmentally damaging pesticides.
Until recently the EPA vigorously enforced laws and the re-registration of pesticides in an attempt to get older, more persistent materials off the shelf. Unfortunately, this process has slowed somewhat with recent political winds. However, even with the slow down, many of the older materials are already gone, replaced by safer and more highly targeted pesticides that have much less effect on "non-targets" and the environment in general.
related page: homeowner insecticides
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