Regional stability and pest increase in high-flying insect migrants over nine decades

Reports of serious and widespread insect declines have been a source of concern for years, but long-term changes in migratory insect communities-which are important components of large-scale ecosystem functioning-are still little understood. Most migratory insects fly at high altitudes, making quantitative investigation problematic. Aerial trapping is the oldest sampling method, and generally still the only one that can provide information on species identity and adequately sample the smaller species. However, aerial sampling is laborious, and thus sampling periods are usually not continuous and sampling sites are sparsely scattered worldwide. To address these issues, we integrated existing data obtained by sampling from aerial platforms (and some high-mountain netting in East Asia) in a comprehensive analysis. We found that, between 1926 and 2017, the aerial density of high-flying migratory insects from samples taken about 200 m above Europe (eastern United Kingdom), North America (southern and central United States), and Asia (east-central China, India, and the Philippines), remained relatively stable overall. Additionally, some key migratory agricultural pests have significantly increased over this period, indicating that the non-pest portion of the aerial migrant community may have declined. Changes in the community structure of high-altitude migratory insects will be closely associated with large-scale ecosystem changes. Thus, apart from continued long-term monitoring of agricultural insect pests and the development of diversified prevention and control methods, there is a need to protect the diversity of non-pest and beneficial migratory insects.