Drivers and pressures behind insect decline in Central and Western Europe based on long-term monitoring data

Abstract

Insect declines have been discussed intensively among experts, policymakers, and the public. Albeit, decreasing trends have been reported for a long time for various regions in Europe and North America, but the controversial discussion over the role of specific drivers and pressures still remains. A reason for these uncertainties lies within the complex networks of inter-dependent biotic and abiotic factors as well as anthropogenic activities that influence habitats, communities, populations, and individual organisms. Many recent publications aim to identify both the extent of the observed declines and potential drivers. With this literature analysis, we provide an overview of the drivers and pressures and their inter-relationships, which were concluded in the scientific literature, using some of the best-studied insect groups as examples. We conducted a detailed literature evaluation of publications on Carabidae (Coleoptera) and Lepidoptera trends with data for at least 6 years in countries of Central and Western Europe, with a focus on agricultural landscapes. From the 82 publications identified as relevant, we extracted all reported trends and classified the respective factors described according to the DPSIR model. Further, we analysed the level of scientific verification (presumed vs correlated vs examined) within these papers for these cited stressors. The extracted trends for both species groups underline the reported overall declining trend. Whether negative or positive trends were reported in the papers, our semi-quantitative analysis shows that changes in insect populations are primarily anthropogenically driven by agriculture, climate change, nature conservation activities, urbanisation, and other anthropogenic activities. Most of the identified pressures were found to act on habitat level, only a fraction attributed to direct effects to the insects. While our analysis gives an overview of existing research concerning abundance and biodiversity trends of carabids and lepidopterans, it also shows gaps in scientific data in this area, in particular in monitoring the pressures along with the monitoring of abundance trends. The scientific basis for assessing biodiversity changes in the landscape is essential to help all stakeholders involved to shape, e.g. agriculture and other human activities, in a more sustainable way, balancing human needs such as food production with conservation of nature.

Fig 1. DPSIR model with examples.

(drivers, pressures, states, impacts, responses; modified after EEA 1999 [35]; shaded in grey: not considered in this publication).

Fig 2. Frequency of extracted pressures for decreasing carabid trends.

These trends are based on 81 extractions in total. Specific pressures classified into pressure classes and (a) their corresponding drivers and states, or (b) their scientific verification levels.

Fig 3. Frequency of extracted pressures for increasing carabid trends.

These trends are based on 26 extractions in total. Specific pressures classified into pressure classes and (a) their corresponding drivers and states, or (b) their scientific verification levels.

Fig 4. Frequency of extracted pressures for decreasing Lepidoptera trends.

These trends are based on 389 extractions in total. Detailed pressures classified into pressure classes and (a) their corresponding driver and state, respectively, or (b) their scientific verification level.

Fig 5. Frequency of extracted pressures for increasing Lepidoptera trends.

These trends are based on 70 extractions in total. Specific pressures classified into pressure classes and (a) their corresponding drivers and states, or (b) their scientific verification levels.