Many beneficial insects and spiders are helping the farmer to defend the crop against pests. In IPM they are therefore called “defenders”.
Some of these defenders are predators, which eat the pest insects. For example the adults and larvae of ladybird beetles eat aphids.
Other defenders are parasites of pests. For example certain parasitic wasps lay their eggs in caterpillars. The larvae of the wasp will feed on the tissue of the caterpillar and kill it in the end.
Also certain pathogens will work as defenders of the crop. For example, there are several viruses, fungi and bacteria that can cause diseases in pest insects. Also certain fungi work as antagonists and protect the crop against fungal diseases.
To make use of this “biological control” an IPM farmer will try to conserve and augment the populations of defenders in the crop field. He will avoid the use of pesticides that kill the defenders. Instead he will try to create an environment which favors their development.