Insect decline: Climate change and farming may have halved some populations

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Warmer temperatures and intense agriculture may be responsible for a 49 per cent decline in insect numbers in some areas, with the tropics worst hit



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20 April 2022

Idea leuconoe butterfly

The paper kite butterfly (Idea leuconoe); insect species are on the decline

Shutterstock/trancedrumer

The combined effects of climate change and agriculture may be responsible for large declines in insect populations around the world, with worst-hit regions seeing a 49 per cent drop in numbers.

“In areas where we have high-intensity farming, coinciding with high climate change, we see reductions of [nearly] 50 per cent in the abundance of insects compared to places [with untouched] vegetation, where very little climate change has occurred,” says Charlotte Outhwaite at University College London.

The study is the first to measure the effects of both warmer temperatures and agriculture on insect biodiversity on a global scale.

“There are a number of studies that looked at a smaller scale, but I’m not aware of any that look at the global effects,” says Outhwaite.

Outhwaite and her colleagues analysed data from 264 earlier studies that together tracked insect biodiversity across a total of 6095 sites around the world. The studies covered 17,899 insect species including beetles, wasps, butterflies and crickets, with data collected between 1992 and 2012.

The team first classified each of the thousands of sites into groups depending on whether or not they had been disrupted by human activity, including if they had been used for high-intensity or low-intensity agriculture. They defined sites of high-intensity agriculture as those in which only one crop type was grown, or high levels of pesticide were used.

By comparing the temperature at each site as recorded some time between 1992 and 2012 with a baseline average temperature measured in the same region between 1901 and 1930, the researchers calculated the extent of local warming over recent decades. They then created a model to assess links between temperature changes and both the number and diversity of insect species.

They found that in regions with the highest temperature rises and high-intensity agriculture, there were 49 per cent fewer insects than in regions where the effects of climate change are minimal and there is little human activity. What’s more, in the regions worst affected by climate change and farming, there were 27 per cent fewer insect species than in regions little affected by climate change and farming.

The team also discovered that insect numbers and diversity declined more in tropical regions compared with non-tropical regions, probably because the insects in tropical regions are less well adapted to temperature rises.

“Insects in temperate regions are much closer to their cold limits than their warm limits, whereas in the tropics, places are just getting too hot for them,” says Outhwaite.

On a positive note, the researchers discovered that fewer insects are lost around areas of low-intensity agriculture – even in the face of climate change – if the agricultural land is surrounded by more natural habitat.

“In sites where there is a lot of natural habitat in the surrounding area, we don’t see as high reductions in biodiversity compared to places with very little natural habitat in the surrounding area,” says Outhwaite.

“The study makes an unequivocal case that increasing global temperatures and agriculture are major drivers of insect loss,” says David Wagner at the University of Connecticut. “It is the first study to show a strong link between climate warming and losses of insect life and by extension the losses of the ecosystem services insects provide for us: pollination, pest control, nutrient recycling and soil formation.”

Journal reference: Nature, DOI: 10.1038/s41586-022-04644-x

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