A crop auxiliary, in a broad sense, is a living organism that provides ecosystem services to facilitate agricultural production. It replaces all or part of the farmer’s work and the inputs brought by the farmer.

This definition includes pest-fighting microorganisms and invertebrates as well as vertebrates such as certain birds, mammals and amphibians that feed on pests or weed seeds. It also encompasses pollinating insects that allow the fertilization of cultivated plants.

In a more restricted meaning, auxiliaries refer to natural enemies, organisms that, through their way of life, development and/or diet, regulate the populations of crop pests. There are three types of natural enemies:

• predators: that feed on other animals (prey)
• parasitoids: hymenoptera (wasps) or dipterans (flies) whose larvae develop at the expense of another individual, resulting in its death
• parasitic microorganisms: nematodes, bacteria, fungi or viruses which lead to the death of pests through their development.

They are naturally found in the soil and in semi-natural habitats. These crop auxiliaries can be bred and subsequently released by import and/or augmentation. They are also intended to be favoured in conservation biological control, thanks to adapted techniques favouring their habitats..

Natural enemies are real allies for farmers in their pest control strategies: this is why in agroecological approaches they promote the development of environments that are able to maintain a natural balance between pests and auxiliaries. This requires appropriate soil management and agrobiodiversity.