Tropical Insect Heat Tolerance Faces Rising Climate Risks

New research indicates that many insects, particularly those in tropical areas, are already living close to the temperatures they can withstand. As the planet heats up, a substantial proportion of species may be unable to “train” their bodies to tolerate warmer conditions.

The issue extends beyond the possible loss of insects themselves. Ecosystems could be affected when pollination, decomposition and natural pest control start to break down.

An international team of researchers assessed heat tolerance in more than 2,000 insect species, then compared the findings with genetic indicators of how well their proteins remain stable under stress.

The scientists examined insects from diverse environments, including cool mountain forests and hot lowlands in East Africa and South America. This provided an overview of where adaptation may be feasible and where it seems severely constrained.

Mountain insects and lowland insects

The findings question a seemingly logical assumption: insects from hotter environments ought to handle heat better, while species should be able to alter their tolerance as conditions shift. The researchers say the pattern is far less consistent.

“Current evaluations of the heat tolerance of insects such as moths, flies, and beetles paint a differentiated – and at the same time alarming – picture,” said lead author Kim Holzmann, a researcher at Julius-Maximilians-Universität Würzburg (JMU).

Holzmann said that capacity to withstand high temperatures does not merely mirror the climate in which a species lives.

The study likewise found that insects’ ability to endure high temperatures does not automatically adjust to their particular environment.

“While species at higher altitudes can increase their heat tolerance, at least in the short term, many lowland species largely lack this ability,” Holzmann said.

This difference is significant because tropical lowlands contain enormous numbers of insect species. Should many of them be unable to raise their heat tolerance, increasing temperatures may expose them to dangerous conditions sooner than anticipated.

Consequences beyond insects

Insects, the researchers emphasise, are far from a marginal issue. They are central to the functioning of many ecosystems. Changes in insect populations can therefore alter everything from plant reproduction to soil condition.

The scientists present the threat as especially severe in tropical regions, where biodiversity is extensive and warming may be unrelenting.

Published in Nature, the study indicates that tropical insects possess only a very restricted capacity to adapt to climate change.

“Rising temperatures could have a massive impact on insect populations, especially in regions with the world’s highest biodiversity,” said Marcell Peters, an animal ecologist at the University of Bremen.

“Since insects fulfill central functions in ecosystems as pollinators, decomposers, and predators, there is a threat of far-reaching consequences for entire ecosystems.”

The reasoning is straightforward. When insects cannot manage the heat, their populations could decline, their activity patterns could change, or their life cycles could be interrupted.

Each outcome can have wider effects. Pollination may become less dependable, decomposition may slow or become irregular, and predator-prey relationships may shift into unfamiliar, unstable arrangements.

Limits may be locked into insect biology

Among the study’s most concerning findings is the possibility that heat tolerance is not as adaptable as is often presumed.

The researchers identified marked variation among insect groups, suggesting that these differences involve more than the places where insects live. They may reflect fundamental biological limitations.

There are also pronounced distinctions between insect groups. The experts link these variations 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,” Peters said.

“The results suggest that fundamental characteristics of heat tolerance are deeply rooted in biology and cannot be quickly adapted to new climatic conditions.”

Where heat tolerance is strongly connected to protein stability, and that stability changes only slowly over evolutionary timescales, rapid climate warming presents a serious mismatch. Species may encounter temperatures rising faster than they can adapt.

This may also clarify why certain insects fare better than others within the same setting. The difference may not be explained by effort, behaviour or acclimatisation alone, but by the molecular construction of their biology.

The Amazon looks especially vulnerable

The researchers identify the Amazon as a region where future heat could become a major source of stress for a large share of insect life.

They are not predicting the disappearance of every insect. Instead, the concern is that many species may pass thresholds beyond which ordinary activity becomes difficult or survival declines.

“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,” Holzmann said.

“Critical heat stress” refers to conditions in which insects may struggle to function normally, reproduce consistently or prevent lethal overheating during the hottest periods.

In an ecosystem as interconnected as the Amazon, the loss of large portions of insect diversity could transform habitats in ways that are difficult to foresee and difficult to reverse.

The authors regard the issue as urgent partly because insect heat tolerance remains inadequately measured, particularly in the tropics. This is notable given insects’ dominance in animal diversity.

Limited data is available

Insects make up roughly 70 percent of all known animal species, with most of them living in tropical regions. Even so, little is understood about how effectively tropical insects handle rising temperatures.

One explanation is the limited amount of experimental data measuring temperature tolerance, alongside insufficient research so far into many insect groups.

For this research, scientists examined the temperature tolerance thresholds of more than 2,000 insect species.

They gathered data during 2022 and 2023 across a range of altitudes in East Africa and South America, from cool mountain forests to hot rainforests and lowland savannas.

The team additionally analysed the genomes of numerous species, investigating protein stability to better establish why some insect groups cope with heat more effectively than others.

This genomic analysis matters because it does more than document what occurs. It seeks to establish why it occurs, connecting differences in heat tolerance to underlying biology that may not be readily “trained” to become something different.

What this means going forward

The research delivers a clear warning. Warming is not simply a matter of species shifting their ranges northwards or to higher ground. Many tropical insects may have little higher ground available and little unused tolerance remaining.

If lowland species cannot increase their heat limits, habitat protection alone may prove insufficient. The climate itself becomes the obstacle.

In effect, the researchers call for greater focus on insect physiology, more measurements in poorly studied regions, and a more realistic understanding of how rapidly living systems can adjust.

In the tropics, where insects underpin so much life, the room for error may be narrower than previously believed.