Where have all the insects gone? More than 75 percent decline over 27 years!

In just 3 decades, insect populations in German nature reserves have plummeted by more than 75%, according to a new study.

The reasons for the decline aren’t clear, but the pattern is consistent over a swath of western and northern Germany, from the region around Bonn and Cologne to the countryside south of Berlin.

For 27 years, members of the Krefeld Entomological Society near Dusseldorf have monitored flying insect populations—everything from parasitic wasps to hoverflies and wild bees—in dozens of nature reserves. In recent years, they noticed a steep decline in their catch, with biomass dropping by some 82% in the summer when insect populations peak.

Their attempts to match the decline with changes in weather, landscapes, and plant coverage—in collaboration with scientists in the Netherlands and the United Kingdom—don’t explain the loss, they report today in PLOS ONE.

The scientists speculate that intensive agriculture surrounding the nature reserves has played a role, but they don’t have data on factors such as pesticide use in neighboring fields.

The decline is likely having wide-ranging effects on plants and other animals, such as insect-eating birds.

The researchers say that better monitoring of these crucial, but overlooked, members of ecosystems is urgently needed. 

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Reference

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Hallmann, Caspar A.; Sorg, Martin; Jongejans, Eelke; Siepel, Henk; Hofland, Nick; Schwan, Heinz; Stenmans, Werner; Müller, Andreas; Sumser, Hubert; Hörren, Thomas; Goulson, Dave; de Kroon, Hans (2017-10-18). Lamb, Eric Gordon, ed. "More than 75 percent decline over 27 years in total flying insect biomass in protected areas". PLOS ONE. Public Library of Science (PLoS). 12 (10): e0185809. ISSN 1932-6203doi:10.1371/journal.pone.0185809.