Further evidence for a global decline of the entomofauna

Abstract

The Anthropocene is characterised by pervasive human-inflicted impacts on a broad range of biota, including insects. In 2019, we reviewed scientific literature quantifying the prevalence and magnitude of insect declines in recent time. Here, drawing upon 40 additional long-term studies, we add evidence that is consistent with our earlier review and some other reviews on the fate of insect populations globally. New data for Greenland, northern Africa, South America, eastern Asia and Australia complement studies from Europe and North America. Temporal trends in insect populations are now derived from 100 long-term studies and refer mainly to the past three or four decades (median 33 years). Data from the 10 major insect taxonomic orders indicate that an average 37% of species are declining in numbers, while populations of 18% species are increasing; the latter taxa mainly involve agricultural herbivores and nuisance pests. Population changes are more pronounced among aquatic insect communities, where 42% of species are declining and 29% increasing. Such changes result in a decrease in biomass across taxa, except for Heteroptera. Changes in species richness and diversity indices are inconsistent and do not reflect intraspecific population changes over time. These trends are observed irrespective of taxon, geography or methodological approach, although a lack of long-term monitoring records prevents a proper assessment for tropical regions.