“It’s not the weather – we humans are causing insect declines”

In various research programs with agribusiness, LIB generates data via advanced monitoring methods that reveal the drivers of the biodiversity crisis. © LIB, C. Scherber

 

Can the weather really be the main cause of insect declines in Central Europe? A recent study in the journal Nature blames (altered) weather conditions for sharp declines in insect biomass. Christoph Scherber, Deputy Director of the LIB, disagrees and – based on his research – sees land-use change as the main cause.

In your view, how important is climate change and associated weather phenomena for insect declines?

Climatic changes do influence insect populations. This has actually been known already since the 1950s – insects are, after all, cold-blooded and therefore fundamentally react strongly to temperature and humidity. In a sense, weather and climate are the “background noise” that has always had an effect on insects. The art now is to precisely work out influences that go beyond this basic noise. There are many experimental studies on the effects of fertilizers, plant protection, soil cultivation, drought, rising temperature and increased CO2 content of the atmosphere on insects, in which causal relationships can be wonderfully compared with each other.

According to your assessment and research, what are the decisive causes of insect declines?

It’s not the weather – it’s us humans that are causing insect declines. The conversion of structurally rich landscapes into infrastructure or intensive agriculture with monoculture and the use of chemicals are, in my opinion, the main causes. For example, in a study conducted in 2015, we specifically investigated the biodiversity of plants, butterflies, grasshoppers and other insect groups in nature reserves. Biodiversity was always particularly low when there was a lot of arable land in the vicinity – and when the protected areas were very isolated from each other.

In 2017, the Krefeld study revealed a 75 per cent decline in insect biomass. Does the new Nature study now provide surprising insights into the causes?

The study does not provide any new insights and rather hinders the debate on the causes of insect mortality. The very approach is wrong: we need experimental study results, such as on intercropping (DIVERsify project),on reduced pesticide use (FINKA project) or on flowering strips (NaPA project), in order to understand insect responses to land use and to find out what we can do differently in the future. The authors of the Nature study present models that are too simple and leave out demonstrably important influencing variables such as land-use in particular. The Krefeld study was not originally designed to discover land use changes – so it is no wonder that one can hardly find causal connections in such a heterogeneous data set. You can’t understand the dynamics of a system just by looking at it. Yet we have excellent data bases from structured biodiversity monitoring, for example from the Dachverband Deutscher Avifaunisten (Association of German Avifaunists) or the Bundesamt für Naturschutz (Federal Agency for Nature Conservation).  We are currently analysing these data as part of a research and development project.

How do you view the Krefeld study and its further development?

The authors of the “Krefeld Study” had themselves noted that the causes of insect declines cannot be precisely identified based on the available data. The study looks back at the insect population in German nature reserves over the past 27 years and has stimulated a debate about causes and protection measures, but also about our knowledge of native species. This knowledge is very patchy. That is why many new studies have been launched since 2017 with the support of the German government. For example, the LIB study GBOL-Dark Taxa.  We are still discovering hundreds of new species in Germany, not to mention introduced species that can only be detected with modern molecular methods like in GBOL. Only if we can classify these species, we can say how many are being lost and why. We need to do long-term research and at the same time act now against insect mortality.

Have we already gathered enough data for insect conservation measures? What does the LIB contribute here?

We are currently conducting various research projects, also EU-wide, in cooperation with farmers (for example the project “BioMonitor4CAP”). Here, we generate data using modern monitoring methods, from which we can identify the drivers of the biodiversity crisis. Enough has long been known to finally implement effective measures to protect insects – measures that are already known to work from field trials. Our studies to date clearly show that biodiversity-enhancing measures such as intercropping, reduction of pesticides or perennial flower strips promote insect biodiversity. We are also conducting research in forests and gardens and have shown concrete solutions here. Instead of looking back, we should look forward and get active for a biodiversity-friendly future.

 

Contact:
Leibniz Institute for Biodiversity Change Analysis (LIB)
Museum Koenig Bonn
Prof. Dr Christoph Scherber
Deputy Director LIB
c.scherber@leibniz-lib.de
+49 (0)228 9122 450

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