Forest hoverfly community collapse: Abundance and species richness drop over four decades

To study insect decline, an important threat to biodiversity, long-term datasets are needed. Here we present a of hoverfly (Diptera: Syrphidae) abundance and diversity in Dutch forest, surrounded by other forests, analyse the variation numbers over four decades. Between 1982 2021, decreased 80%. Until 1990, showed strong decrease 10.9% per year, mainly nationally rare species with carnivorous larvae exposed air. From stabilised, whereas from 2000, second period decline 9.0% year occurred, very common species. Species richness also declined strongly between 1979 2021: total number observed five monitoring days dropped 44% those 43 years. The characteristic set dry-forest disappeared at site 19 9 early on, (1979–1984) that coincided intense nitrogen input acidification caused agriculture same region. more recent is likely factors outside as forest management conditions remained constant. Continued influx nutrients pesticides regional level, well climate change possible causes decline. Research needed quantify their relative effects.