Climate, large agriculture halving insect populations

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Paris (AFP)- Global warming and intensive agriculture are driving insect populations down by nearly half compared to areas less affected by rising temperatures and industrial agriculture, researchers said Wednesday.

The researchers measured both insect abundance and species numbers in regions around the world and compared them to insects in more pristine habitats.

The study published in Nature found that the double whammy of global warming and shrinking habitats not only affected the population, but also caused a 27% drop in species diversity.

“Reductions are greatest in the tropics,” lead author Charlie Outhwaite, a macroecologist at University College London’s Center for Biodiversity and Environment Research, told AFP.

But fewer data from the tropics, which are the most biodiverse, mean the global decline in insects is likely worse than the study’s figures suggest, she said.

The calculations may also be overly conservative because the areas used to assess change – although the most pristine on the planet – have already been degraded to some degree by human activity.

Although consistent with earlier estimates of insect decline, the new findings are based on different methodologies.

Covering 18,000 species, from beetles to butterflies to bees, the study relied on 750,000 data points collected from 1992 to 2012 at 6,000 sites.

“Previous studies have been done on a small scale on a limited number of species or groups of species,” Outhwaite said.

The consequences of insect decline are significant.

About three-quarters of the world’s 115 major food crops depend on animal pollination, including cocoa, coffee, almonds and cherries.

Some insects are also crucial for pest control, especially other insects.

Some insects are also crucial for pest control – especially other insects Youri KADOBNOV AFP/File

Ladybugs, praying mantises, ground beetles, wasps and spiders all play a crucial role in controlling insect pests, from aphids and fleas to cutworms and caterpillars.

Insects are also crucial for waste decomposition and nutrient cycling.

“A catastrophic record”

The study is the first to examine the combined impact of rising temperatures and industrial agriculture, including the widespread use of insecticides.

“We often only consider one driver of change, such as land use, when in reality many drivers will impact the same space,” Outhwaite said.

The interaction between these drivers, the study shows, is worse than if they had acted independently.

Even without climate change, the conversion of a rainforest to agricultural land leads to drier and warmer areas due to the removal of vegetation that provides shade and traps moisture in the air and soil. floor.

Add a degree or two of warming, and these regions get even hotter and drier, pushing some insect species to or beyond their limits.

In some areas, insects now experience long periods of temperatures above the highest extremes of less than a century ago.

In some regions, insects now experience long periods of temperatures above the highest extremes of less than a century before.
In some regions, insects now experience long periods of temperatures above the highest extremes of less than a century before. ORLANDO SIERRA AFP/File

So far, intensive agriculture and habitat loss have been the main drivers of insect decline.

Previous research, for example, estimates that the number of flying insects in Europe has fallen by an average of 80%, causing bird populations to decline by more than 400 million in three decades.

“We know you can’t keep losing species without ultimately causing a catastrophic outcome,” said Tom Oliver, professor of applied ecology at the University of Reading.

“You can’t keep pulling rivets out of an airplane without it eventually falling out of the sky.”

agricultural hope

The new study points to a strategy that could extend a lifeline to endangered insects.

Areas with low-intensity agriculture — less chemicals, less monoculture — that were surrounded by at least 75% natural habitat saw only a 7% drop in insect abundance.

But if the density of the surrounding natural habitat fell below 25%, the insect population fell by nearly two-thirds.

A bumblebee walks towards a flowering tomato plant
A bumblebee walks towards a flowering tomato plant Patrick Pleul dpa/AFP/File

“I think this discovery gives us hope that we can successfully design landscapes to produce food where biodiversity can thrive,” Jane Hill, professor of ecology at the University of York, told Science Media. Center.

Insects make up about two-thirds of all terrestrial species and have been the basis of key ecosystems since their emergence nearly 400 million years ago.

Moles, hedgehogs, anteaters, lizards, amphibians, most bats, many birds and fish all feed on insects.

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