A few species of natural enemy are particularly important as they are resistant to broad-spectrum insecticides and are able to prevent serious outbreaks of one or more important pests. These are key natural enemies.
Key natural enemies are easier to exploit for pests that do not damage the fruit directly and can thus be tolerated at low to moderate levels in orchards. The most important key natural enemies identified to date for apple and pear pests are:
- Organophosphorus insecticide resistant strains of the orchard predatory mite, Typhlodromus pyri, which prevent pest mite outbreaks on apple.
- The common European earwig, which is resistant to insecticides and prevents woolly aphid outbreaks as well as regulating populations of many other pest species
- Parasitic wasps, which parasitise and regulate populations of leaf mining moths. The parasitic wasp Platygaster demades attacks apple leaf midge.
- Predatory flower bugs (anthocorids) which regulate pear sucker populations