Biological control is one of the essential services provided by biodiversity. It is carried out by natural enemies, which help to bring the populations of plant-feeding insects below the threshold where they are no longer deemed harmful. Ladybirds, parasitoid wasps and spiders are formidable predators that can help keep pests at bay.
To examine the effect of urbanisation on this ecosystem service, a study was conducted by an international team including INRAE, the Centre of Ecological Research in Hungary, and the Technical University of Munich in Germany. The researchers used a meta-analysis approach, which synthesises the results of several scientific articles dealing with the same issue.
The team of scientists identified 52 studies conducted in different cities around the world. They found that abundance of sap-feeding insects, such as aphids or mealybugs, increase in urban zones compared to rural areas by 44%. Conversely, the number of natural enemies with weak dispersal capacity is lower.
Their results go even further, indicating that as the level of urbanisation increases, the level of biological control provided by natural enemies decreases. In cities, insect pests, and in particular biting and sucking insects, are therefore less well regulated by their natural enemies. These insects can be considered problematic in urban areas because they cause severe damage to plants and can make pavements and other surfaces sticky.
However, natural enemy populations can be boosted through specific management practices. For example, leaving areas of diverse vegetation (including tall grasses, shrubs and trees) alone, with only occasional mowing and ensuring that cuttings are left on the ground. This provides shelter and favourable environmental conditions for helpful predators.
Thus, this study highlights the value of using nature-based solutions* and reducing land artificialisation in cities to significantly contribute to the restoration of insect communities and their ecological functions.
* Actions to protect, sustainably manage and restore natural or modified ecosystems to directly address societal challenges in an effective and adaptive manner, while ensuring human well-being and producing benefits for biodiversity. (Source IUCN)
Korányi, D., Egerer, M., Rusch, A., Szabó, B. & Batáry, P. (2022) Urbanization hampers biological control of insect pests: A global meta-analysis. Science of the Total Environment 834: 155396. https://doi.org/10.1016/j.scitotenv.2022.155396