study
Weather influence on insect decline – controversial debate
Bees buzz around the gable of a house covered in ornamental vines. photo
© Karl-Josef Hildenbrand/dpa
For years, researchers have been warning of massive insect deaths with fatal consequences. A study now brings the weather into play as an important factor. Research colleagues warn against drawing false conclusions.
According to a study, an accumulation of unfavorable weather conditions had a noticeable influence on the observed decline of flying insects in Germany in recent decades. A research team reports that evaluated weather data is consistent with the decline in insect mass Jörg Müller from the University of Würzburg in the journal “Nature”. The study is being discussed very controversially among researchers.
The assessments range from “significant gain in knowledge” to “Nature should not have published it in this form”. So far, intensive agriculture, but also light pollution and increasing surface sealing are suspected to be the causes of the decline in insects.
Müller’s researchers conclude in a short German report on the current study that weather anomalies caused by climate change have a decisive influence on insect development. This includes, for example, warm, dry weather during the wintering period or wet and cold conditions during the flight period in summer.
Some experts may find interesting aspects of the new study. However, it is emphasized that a mix of different factors is most likely responsible for the insect deaths. Researchers point out that intensive agriculture particularly threatens biodiversity – in contrast to the total number of insects.
Previous work reanalyzed
In 2017, a team led by Caspar Hallmann from Radboud University in Nijmegen (Netherlands) discovered a dramatic decline in the mass of flying insects in parts of Germany while analyzing data from Krefeld entomologists. Accordingly, the total mass had decreased by more than 75 percent from 1989 to 2016. In search of possible reasons, the scientists examined the influence of climate factors, agricultural use and certain habitat factors. However, the analysis did not provide a clear explanation. The new study now links these findings and the researchers’ own surveys with weather data.
Surprising observation
According to his own statements, the ecologist Müller saw a particularly large number of insects in the forest and fields in the spring of 2022. Because, according to the University of Würzburg, this made him suspicious, he investigated the matter with colleagues from the TU Dresden, the TU Munich and the University of Zurich. Using net traps (malaise traps) set up in Bavaria, they caught flying insects, which were weighed in their entirety and compared with catches since 1989.
“We found a biomass that was on average almost as high as the maximum values from the Hallmann study,” explained Müller, according to the University of Würzburg. The research team then reanalyzed the data from the Hallmann study, also taking the weather into account. The team found that in the years from 2005 onwards, insects were predominantly affected by negative weather conditions. In the summer of 2021 and 2022, however, the weather was consistently favorable for insects. This explains the relatively high insect biomass in 2022, the scientists concluded.
Controversial debate
For Axel Ssymank from the Federal Agency for Nature Conservation, the study has “a number of serious methodological weaknesses,” as he explained to the German Press Agency. This means, among other things, that “no statements can be made about the relative importance of the decline in insects due to changes in agricultural use.” However, there is “a kernel of truth in the publication” when it comes to correlations with extreme weather events and climate change.
Hans-Peter Piepho, head of the biostatistics department at the University of Hohenheim, said of the study: “Under no circumstances should it be concluded from the study that weather phenomena alone can explain the dramatic loss of insect biomass in the Hallmann study.” Even if Müller’s team demonstrated a major influence of weather on insect biomass, this does not mean “that other factors such as pesticide use and changes in land use cannot also have a major influence.”
Christoph Scherber from the Leibniz Institute for the Analysis of Biodiversity Change in Bonn is very critical of the study, saying it does not provide “any new insights.” The authors present models that are too simple and leave out the demonstrably important influencing factors – especially land use. “The core message of the current study is absolutely fatal and should not have been published by Nature in this form.”
For Josef Settele from the Helmholtz Center for Environmental Research in Halle/Saale, the study represents “a significant gain in knowledge”. However, he believes that certain aspects are not taken into account, including the use of pesticides. “We cannot avoid thinking and tackling climate change, land use and the loss of biodiversity together,” summarizes Settele.
In principle, it is clear that insect populations are highly dependent on the weather, said Johannes Steidle, director of the Zoological and Veterinary Museum at the University of Hohenheim. Nevertheless, he sees the intensification of agriculture as the main cause of insect deaths. “This current study doesn’t change that.”