Planet may get too hot for tropical insects, warn scientists

MANY tropical insects could be wiped out by the end of the century because of climate change, scientists have warned.

Insects such as beetles, butterflies, aphids and other insects living in tropical areas such as rain forests will be unable to cope with dramatic temperature rises predicted for the next 100 years, according to research by the University of Washington.

Scientists say insects in the tropics are far more sensitive to temperature rises than those elsewhere. They predict it will be difficult for them to survive temperature rises of up to five degrees predicted by 2100.

The team found that even though temperature changes might not be as extreme in tropical areas as in more temperate regions, species in those areas have a far greater risk of extinction with warming of just a degree or two. That is because they are used to living within a much smaller temperature range.

In contrast, Arctic species can be used to living in temperatures ranging from below zero to 16C and typically live at temperatures well below their maximum limit.

A decline in insect numbers could have huge impacts on the food chain and the pollination of plants.

Joshua Tewksbury, assistant professor of biology at the University of Washington, said: "What we found was that if we use climate models to move the climate forward and ask how are they going to do in the future, the insects living in the tropics are already living in climates that are quite warm compared to what they want to live in.

"There is not a very big buffer – there's not lot of space for the climate to increase. A small amount of warming leads to decline in these species.

"A 5C increase in many tropical locations would be very problematic for a large number of insects."

The team studied 38 insects to see how their ability to tolerate temperature change varies across the planet.

Unlike temperate areas such as the UK, where there are more defined seasons, there is little way insects can escape the heat in tropical regions by adapting.

"If you warm up a tropical rain forest by 4C, it's warmed up all year long, so there's no way they can hide," Prof Tewksbury explained.

"There's a lack of seasonabilty so there's no way they can adapt to live in the spring."

And unlike warm-blooded animals, cold-blooded organisms cannot regulate their body temperatures by growing a fur coat when it is cold, or shedding it when it gets warm.

They are limited to seeking shade when it is too hot or burrowing into the soil. If it is still too hot in the shade they will not be able to survive.

Prof Tewksbury said it is more difficult to notice when species living in tropical areas are being affected by climate change.

In temperate regions with seasons, it is easy to see when a plant such as a daffodil flowers at the wrong time of year, but in areas without seasons changes can be more difficult to spot.

"Part of the reason we decided it was important to do the research was because there's been a lot of emphasis on more temperate regions and not as much research being done in tropical areas," he said.

Curtis Deutsch, assistant professor of atmospheric and oceanic sciences at the University of California, who was joint author of the paper detailing the research, said: "Many tropical species can only tolerate a narrow range of temperatures because the climate they experience is pretty constant through-out the year.

"Our calculations show that they will be harmed by rising temperatures more than would species in cold climates.

"Unfortunately, the tropics also hold the large majority of species on the planet."

• The research is published in the Proceedings of the National Academy of Sciences.

Among the species at risk

Leaf beetle: The common name for beetles in the Chrysomelidae family. There are more than 35,000 species and many live in tropical areas, such as the cloud forests in Ecuador.

Tropical butterflies: These include the beautiful Blue Morpho (Morpho menelaus), which lives in South American rain forests.

Bark beetle: Members of the Curculionidae family. Many live in tropical forests and are known for their habit of reproducing in the inner bark of trees.

Dung beetles: Members of the Scarabaeidae family, they feed partly or exclusively on faeces. They live in tropical areas, as well as temperate climates.

Fruit fly: These small flies belongs to the Drosophilia family and feed on rotting fruit. Most species are in tropical regions.

Aphid: Belongs to the Aphidoidea family. The minute plant-feeding insects are also known as plant lice. They live all over the world, including tropical regions.