A global study was conducted by an international team of scientists from the ELKH Centre of Ecological Research (CER), Hungary, the Technical University of Munich, Germany and the National Research Institute for Agriculture, France to examine the effect of cities on the ecosystem service.  The researchers have pointed out that the populations of sap-feeding pests are weakly regulated in cities and advised nature-based solutions to decrease the harmful effects of urbanization. Their findings were published in the international journal Science of the Total Environment.

At least half of the insect species living on our planet feed on plants (i.e. they are herbivores), and among them, insect pests are one of the greatest threats to cultivated and naturally growing plants. Therefore, controlling their numbers is essential for the economy and plant health. Unfortunately, plant protection against pests mainly relies on synthetic chemicals in many ecosystems, which substantially impact the environment and human health. To mitigate these adverse effects, applying environmentally-friendly practices is needed, especially in cities where more than half of the world’s population lives.

Biological control is one of the most essential services delivered by biodiversity, with an estimated economic value of more than 400 billion dollars per year worldwide. Biological pest control is provided by natural enemies that contribute to limiting pest populations under a certain threshold where they may no longer be considered pests. These are predators that primarily obtain food by killing and consuming other organisms, such as ladybird beetles that feed on aphids or parasitoids whose larvae feed on their host’s bodies, such as parasitic wasps that lay their eggs on caterpillars.

The researchers used a statistical method called meta-analysis that combines the results of multiple scientific papers addressing the same question. They included 52 studies performed in different cities worldwide. Researchers found that the number of sap-feeding pests (i.e. insects like aphids and scales that use sucking mouthparts to feed on sap and plant cells) was much higher, whereas that of arthropod natural enemies with poor dispersal ability was lower in urban areas (e.g. those neighborhoods with more impervious built-up surface) than in more natural rural areas (e.g. those neighborhoods with more green space). They also showed that the level of biological control provided by arthropods weakened with increasing levels of urbanization.

Their findings illustrate that the populations of sap-feeding pests are weakly regulated in cities. The first author of the study, Dr. Dávid Korányi from CER, said, “These herbivores are considered one of the most problematic pests in urban areas as they can strongly deteriorate the condition of plants and produce a large amount of honeydew, making plants, sidewalks, and other surfaces sticky. Based on the results, it can be assumed that natural enemies, especially predators with poor dispersal ability (for instance, earwigs and some carabid beetles), can contribute to the effective biological control of insect pests.”

The leader of the study, Dr. Péter Batáry from CER, said, “We can support these beneficial arthropods with contiguous and natural green areas with less intensive management practices in cities. For example, diverse vegetation (including tall grasses, shrubs and trees), occasional mowing, and limited removal of leaf litter and dead woods can provide them shelters and optimal environmental conditions to be present permanently in urban areas.”

Thus, this study may advise developing nature-based solutions and reducing imperviousness in cities to significantly contribute to restoring ecological communities and functions that can reduce the environmental footprint of urbanization.

Publication:

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