The decline of insects in German forests and grassland is "frightening" particularly in the vicinity of intensively farmed land, scientists have warned.
An international research team led by scientists from the Technical University of Munich (TUM) collected more than one million insects between 2008 and 2017 at 300 sites across the German states of Brandenburg, Thuringia and Baden-Wurttemberg.
The results, published in the Nature journal on Wednesday, show that of many of the nearly 2,700 insect species have declined by over a third in ten years.
"In recent years, certain rare species could no longer be found in some of the regions studied," TUM said in a statement.
Insect biomass in the forest the scientists studied decreased by approximately 40% since 2008 and the situation is "even more alarming" in grasslands where it has decreased to only one-third of its former level.
"A decline of that scale over a period of 10 years came as a complete surprise to us — it is frightening, but fits the picture presented in a growing number of studies," Wolfgang Weisser, the co-initiator of the project, said.
No type of forest or grassland — from sheep pastures to meadows that are regularly mowed and fertilised to unused forests and protected areas — were spared from the decline. However, the biggest losses were recorded in grasslands surrounded by intensively farmed land.
Scientists identified species unable to travel far as the most heavily impacted.
"To decide whether it is a matter of the more mobile forest-dwelling species having more contact with agriculture, or whether it has something to do with living conditions in the forests, further study will be needed," Martin Gossner, a former TUM researcher, added.
According to the UN Environment programme, insects, which make up about half of all known living organisms, are crucial to ecosystems because they play key roles in pollination and nutrient cycling, as well as in the food chains of birds and other insectivores.
It attributed habitat loss by conversion to intensive agriculture as the main driver of the declines. The use of agrochemical pollutants and climate change are additional causes, it stated, calling for "rethinking of current agricultural practices, in particular, a serious reduction in pesticide usage."