Locust Swarms Could Expand Their Range in a Hotter, Stormier World

Rising temperatures could expand the area of the globe under threat from crop-devouring locusts by up to 25 percent in the coming decades, a new study found, as more places experience the cycles of drought and torrential rain that give rise to biblical swarms of the insects.

Desert locusts for millenniums have been the scourge of farmers across northern Africa, the Middle East and South Asia. They love hot, dry conditions, but they need the occasional downpour to moisten the soil in which they incubate their eggs.

Human-caused warming is heating up the locusts’ home turf and intensifying sporadic rains there. That is exposing new parts of the region to potential infestations, according to the study, which was published Wednesday in the journal Science Advances.

“Given that these countries often serve as global breadbaskets and are already grappling with climate-driven extremes like droughts, floods and heat waves, the potential escalation of locust risks in these regions could exacerbate existing challenges,” said Xiaogang He, one of the study’s authors and an assistant professor of civil and environmental engineering at the National University of Singapore.

Other scientists cautioned, however, that climate change is also affecting locust threats in another important way. When they are not gathering by the tens of millions and laying waste to whole landscapes, these insects lead meek, solitary lives in arid zones. As the planet warms, some of these areas could become too hot and dry even for the locusts, leaving smaller territories in which they can multiply and congregate.

This might make it easier to use pesticides to stop outbreaks before they can morph into all-out plagues, said Christine N. Meynard, a researcher at the National Research Institute for Agriculture, Food and Environment in Montpellier, France. “If you can focus on fewer areas” for fighting locusts, “it’s a lot better,” said Dr. Meynard, who wasn’t involved in the new study.

Locust invasions might be best known as a form of divine punishment, but scientists have long understood that the insects’ lives are linked intimately with weather, climate and ecology.

For long stretches of time, desert locusts stay scattered and out of sight in dry places including the Sahara and the Sahel in Africa and the Thar Desert in India and Pakistan. When it rains, their eggs flourish and so does the surrounding vegetation, giving the hatchlings lots to munch on.

As the land dries out again, they begin to convene in the spots where greenery remains. They then take flight in swarms to search for more food, darkening skies and gobbling up crops across some of the poorest places on the planet.

In 2019, the worst locust infestations in a generation began descending on a stretch of the globe from East Africa to central India. The United Nations Food and Agriculture Organization and its partner agencies undertook a vast operation to protect crops and livestock and to secure food supplies for tens of millions of people.

Dr. He and his colleagues used mathematical modeling to examine how climate factors shape the way locust invasions unfold across large areas. They found that the timing of seasonal rains across the region can cause far-flung places to be at disproportionate risk of experiencing swarms at the same time.

India and Morocco, for instance, are thousands of miles apart. And yet locust plagues are highly likely to be synchronized in the two countries, the researchers found. Similarly for Pakistan and Algeria. “Concurrent locust infestations have the potential to trigger widespread crop failures, jeopardizing global food security,” Dr. He said.

Based on what he and his colleagues determined about how rainfall, temperatures, soil moisture and winds affect where locusts end up, they also predicted how global warming might change the picture.

They estimated that the pests’ total range could expand by 5 percent to 25 percent before 2100, depending on how much warmer the planet gets. Some places that don’t have locusts today could start seeing them in the coming decades, the researchers found. These include areas of Afghanistan, India, Iran and Turkmenistan.

A different species, the South American locust, plagues farms in Argentina, Bolivia, Brazil, Paraguay and Uruguay. Other research has predicted that warming will increase the geographic range of that pest, too.

Climate and ecology aside, Dr. Meynard and other researchers see sociopolitical conditions as another important factor behind locust risks. In conflict-ravaged Yemen, for instance, pest populations were able to grow unchecked in recent years, which might have worsened the outbreaks in 2019 and 2020.

More stable countries have improved their monitoring and management of locusts, Dr. Meynard said. “There has been some progress, definitely,” she said.

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