Mitigating the precipitous decline of terrestrial European insects: Requirements for a new strategy

Severe decline in terrestrial insect species richness, abundance, flying biomass, and local extinctions across Europe are cause for alarm. Here, we summarize this decline, and identify species affected most. We then focus on the species that might respond best to mitigation measures relative to their traits. We review apparent drivers of decline, and critically reflect on strengths and weaknesses of existing studies, while emphasising their general significance. Generality of recent scientific findings on insect decline have shortcomings, as results have been based on irregular time series of insect inventories, and have been carried out on restricted species sets, or have been undertaken only in a particular geographical area. Agricultural intensification is the main driver of recent terrestrial insect decline, through habitat loss, reduced functional connectivity, overly intense management, nitrogen influx, and use of other fertilisers, as well as application of harmful pesticides. However, there are also supplementary and adversely synergistic factors especially climate change, increasingly intense urbanisation, and associated increase in traffic volume, artificial lighting and environmental pollution. Despite these various synergistic impacts, there are mitigating factors that can be implemented to stem the precipitous insect decline. Science can provide the fundamental information on potential synergistic and antagonistic mechanisms of multiple drivers of insect decline, while implementation research can help develop alternative approaches to agriculture and forestry to mitigate impacts on insects. We argue for more nature-friendly land-use practices to re-establish Europe’s insect diversity.