Besides a sharp decrease in the total biomass of flying insects in German nature reserves, the diversity of species has also declined. Researchers from Radboud University have shown that this applies to hoverflies. Insect populations have declined across the board, especially among more common species. The researchers will publish their results on 12 January in a special edition of PNAS that is devoted entirely to insect declines.
Starting in 1989, entomologists trapped insects at various German nature reserves. After 27 years they weighed the total biomass at the research facility in Krefeld. In addition, they counted all hoverflies that were captured in six insect traps in 1989 and 2014. They identified 162 different hoverfly species. “It was an enormous job for the Krefeld entomologists to remove nearly twenty thousand hoverflies from the large insect biomass samples and identify them, but this has provided an extremely valuable dataset,” says co-author Eelke Jongejans.