Urbanisation appears to be another key factor for insect decline. This is shown by a study in which the impact of climate and land use on insects was disentangled for the first time.

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Worldwide, the quantity and diversity of insects are declining: scientists have reported more and more evidence for this in recent years. In politics and society, these findings have raised great concern.

Researchers attribute the decline in insect numbers on the one hand to changes in land use, for example to the increase in large monocultures such as maize and rape, but also cite climate change with increased temperatures and drought as a cause.

Previous Data Have Weaknesses

However, these findings seem to have weaknesses, says animal ecologist Professor Jörg Müller from the Biocentre of Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany. Among other things, the underlying studies so far do not represent the diversity of insect species well enough or only consider short periods of time and small areas.

A research team of the Bavarian LandKlif network, coordinated by JMU, now wanted to remedy this shortcoming. The results of the study have been published in the journal Nature Communications. They show that urbanisation is another key factor for the overall decline of insects.

Study at 179 sites from low to high elevations

From Lower Franconia to Upper Bavaria, the researchers placed traps to collect flying, crawling and jumping insects in spring 2019. These Malaise-traps were located at 179 sites, from the lowlands to elevations above 1100 meters in the Bavarian Forest and the Alps. They were located in forests, on meadows and fields as well as in settlements, embedded in semi-natural, agricultural and urban landscapes.

The researchers emptied the traps every 14 days for an entire vegetation period. They determined the biomass of the insects caught and identified the individual species using DNA sequencing.

Insects benefit from higher temperatures

"In this study, we were able for the first time to disentangle the impact of climate and land use on insects in a Central European landscape," explains Jörg Müller. "Interestingly, temperature at the local site as well as annual temperature have only positive effects on the biomass and diversity of insect populations. The form of land use, on the other hand, has different effects on biomass and diversity."

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