A study focused on Swiss reconstructs for the first time almost a century of changes in the diversity of various groups of insects and reveals that its greatest decline occurred in the middle of the 20th century.
The study, published in Nature Ecology & Evolution, shows that butterflies and beetles that feed on dead wood (saproxylic) suffered sharp declines, especially in that period, coinciding with agricultural intensification, mechanization and the simplification of landscapes.
Although the study focuses on Switzerland, its results help to understand the effects of these processes on biodiversity in other European countries. In fact, the international scientific team includes the participation of the Doñana Biological Station (EBD-CSIC).
The research was led by Agroscope within the framework of the INSECT program and is based on historical and current records of more than 800 species of butterflies and saproxylic beetles collected between 1930 and 2021 in Switzerland: “People have always been fascinated by large insects such as butterflies and beetles. Therefore, there are numerous historical specimens, as well as records in modern observation applications”explained Felix Neff, Agroscope researcher and first author of the study.
The results
The results indicate that saproxylic beetles decreased until approximately 1960, but later they stabilized and in some areas recovered levels similar to those of 1930.
Instead, butterflies continued to decline until the 1980s and have failed to fully recover. On average, butterfly species richness is 12% lower today than in 1930, with sharper declines in the most intensely cultivated and urbanized regions.
The study reveals that the greatest declines occurred during the period of agricultural intensification between 1950 and 1980, marked by greater mechanization, landscape homogenization and the use of fertilizers and pesticides.
In forests, logging for timber production and the removal of old trees and timber reduced the available habitat for many specialized beetle species.
“Most butterflies depend on sunny, nutrient-rich open spaces, and many deadwood beetles depend on mature forests and large amounts of dead wood. These two groups are, therefore, representative of the state of these habitats, on which many other species depend,” explained Kurt Bollmann, from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).
Partial recovery
However, the research also indicates signs of partial recovery following the development of forest conservation policies, the creation of areas with dead wood and mature forests, as well as some agri-environmental measures.. Furthermore, the climate warming has benefited some species adapted to higher temperatures, especially among wood-feeding beetles.
“This study shows that insect communities do not all respond the same: some species can recover when habitat conditions improve, but many specialized species are still in decline or have not recovered their historical levels”stated Carlos Martínez-Núñez, researcher at the Doñana Biological Station and member of the study team.
The conservation message, in his opinion, is clear: “It is not enough to stop the loss of biodiversity; we need to restore the quality and heterogeneity of habitats, reduce pressure on agricultural landscapes and maintain key elements such as flowers, semi-natural margins, old trees and dead wood.”