However, they are used only when absolutely necessary and applied so that they won't harm the beneficial insects. Some chemicals only affect certain groups of insects, e.g. pirimicarb is sprayed to control aphids, and is less toxic to many other insects, such as ladybird larvae. Chemicals are applied at specific times appropriate to the insects' life cycles. Finally, application methods are designed to minimize the amount of chemical that is used. For example, spot treatment of affected plants is often used instead of blanket spraying the whole glasshouse.
Parasites live on or in the pest, eventually killing it.
Pathogens, such as bacteria, fungi and viruses, cause disease to pests. A bacterium called Bacillus thuringensis infects and kills caterpillars. These beneficial organisms can be encouraged by providing appropriate food and shelter, and not using chemicals that could harm them. Using IPM - issues and benefits IPM is far better for the environment than using pesticides alone. It is also more effective.