Drivers of insect decline: direct, indirect, and combined pressures

Reductions in insect biodiversity are widely documented and result from numerous pressures that operate from local to global scales. Identifying and synthesizing information on these drivers has become a central focus of research over the past decade, yet existing reviews often emphasize a limited set of well-established threats. Here, we provide a policy-oriented review of the drivers of insect decline, structured explicitly around the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) assessment framework and accompanied by statements of confidence to facilitate direct uptake into biodiversity assessments. We integrate evidence on both widely recognized drivers and a broader suite of pressures that remain comparatively understudied. The impacts of large-scale drivers of insect decline, such as land-use change and climate change, are well established and broadly align with those seen to threaten other taxa. Yet, many other threats, such as insecticides and light pollution (among others), pose disproportionate harm to insects but are not fully understood and remain important areas of research. It is also the case that most insect populations are experiencing multiple stressors simultaneously, and the combined effects of these pressures remain unclear. Despite this uncertainty, many threats to insect biodiversity are largely understood, and we know enough to form broad expectations for future responses and to develop action plans.