“Current evaluations of the heat tolerance of insects such as moths, flies, and beetles paint a differentiated – and at the same time alarming – picture,” explains study author Dr. Kim Holzmann, researcher at the Chair of Animal Ecology and Tropical Biology of the Julius-Maximilians-Universität Würzburg (JMU).

According to the study, insects’ ability to tolerate high temperatures does not simply adapt to their respective environment. “While species at higher altitudes can increase their heat tolerance, at least in the short term, many lowland species largely lack this ability,” says Holzmann.

Threatening consequences for entire ecosystems

The study, published in Nature, makes it clear that tropical insects have only a very limited ability to adapt to climate change. Dr. Marcell Peters, animal ecologist at the University of Bremen and study author, says: “Rising temperatures could have a massive impact on insect populations, especially in regions with the world's highest biodiversity. Since insects fulfill central functions in ecosystems as pollinators, decomposers, and predators, there is a threat of far-reaching consequences for entire ecosystems.”

There are also striking differences between different insect groups. The researchers attribute these differences to the structure and heat stability of proteins. “These properties are relatively conserved in the evolutionary family tree of insects and can only be changed to a limited extent. The results suggest that fundamental characteristics of heat tolerance are deeply rooted in biology and cannot be quickly adapted to new climatic conditions,” Peters says.

The prognosis for the Amazon region is particularly alarming, as Holzmann emphasizes. “If global ecosystems continue to warm unabated, expected future temperatures will lead to critical heat stress for up to half of the insect species there,” so the JMU biologist.

Limited measurement data currently available

Insects account for around 70 percent of all known animal species, and most live in the tropics. Nevertheless, little is known about how well tropical insects cope with rising temperatures. One reason for this is the low amount of experimental measurement data on temperature tolerance and the insufficient research on many insect groups available to date. An international research team conducted the study and received funding from the German Research Foundation.

For the study, the scientists investigated the temperature tolerance limits of more than 2,000 insect species. Data was collected in 2022 and 2023 at various altitudes in East Africa and South America, ranging from cool mountain forests to hot rainforests and lowland savannas. The team also analyzed the genomes of numerous species to study the stability of their proteins and better understand why some insect groups tolerate heat better than others.