As global warming accelerates, scientists say it’s more important than ever to understand how climate extremes such as heatwaves, droughts and extreme rains affect locust outbreaks that can destroy billions of dollars worth of crops within a few weeks when the insects swarm.
A study published today in Science Advances suggests that, if global warming isn’t curbed, west India and west central Asia could become locust hotspots in the decades ahead, raising new challenges for control efforts, and further threatening food security and livelihoods in already vulnerable regions.
The scientists said suitable locust habitat could increase about 5 percent in a low-emission future with limited warming, compared to locust distribution between 1985 to 2000. But with high emissions and greater warming, it could increase by as much as 13 to 25 percent during the 2065 to 2100 period.
If the global temperature keeps rising, it “may create favorable conditions for locust development in previously low-temperature regions,” said co-author Xiaogang He, assistant professor for civil and environmental engineering at the National University of Singapore.
“The projected high likelihood of extreme rainfall could provide moist soil for egg incubation” in new areas, he said. Increased moisture also boosts vegetation that feeds and shelters locusts. The potential new habitat areas are dominated by deserts and dry shrublands with “sandy and silty soil, which is a precondition for locust breeding,” he added.
While the study looked at linkages between locust populations and movements and climate variables, he said they did not try to make a direct causal link showing now physical mechanisms of warming affect any particular outbreak. Instead, the modeling is aimed at getting a better understanding of the risk of synchronized outbreaks at a continental scale. That could help refine early warning systems, which would definitely need more detailed local on-the-ground measurements and observations to be effective, he added.
“Here, we develop a data-driven framework to assess the compound risk of locust outbreaks in the Middle East and North Africa,” the authors wrote in the study. “A warming climate will lead to widespread increases in locust outbreaks with emerging hotspots in west central Asia, posing additional challenges to the global coordination of locust control.”
During the last major outbreak in the early 2020s, locusts ravaged crops, trees and pastures across Africa, the Arabian Peninsula and South Asia, which affected 25 million people in 23 countries and caused $1.3 billion in damage. At the peak of the infestation, live swarms interfered with air traffic and locust carcasses blocked rail lines. Desert locusts are the most destructive migratory pests on the planet, with swarms that can travel 90 miles per day, eating the same amount of food as 35,000 people.
Can Control Measures Keep Pace With Climate Change?
In one phase of its life, the desert locust (Schistocerca gregaria) that affects East Africa and South Asia is a loner, feeding on local vegetation in isolated pockets. But long regional droughts ending with soaking rains favor the development of destructive swarms—and global warming is intensifying both of those extremes.
The new paper bolsters other findings about how global warming affects the threat of locust plagues and adds nuance about climate links between simultaneous outbreaks in different regions, said Martin Huseman, science director of the State Museum of Natural History in Karlsruhe, Germany.
“It’s not surprising, as the climatic factors largely determine the outbreaks, and areas with similar climate will have similar risks,” said Huseman, who has studied locusts, but was not an author on the new paper.
But the risks increase dramatically if global warming continues or accelerates, as suggested by recent research. That would lead to a northward shift of locust habitat, “resulting in the emergence of new hotspots in West India, Iran, Afghanistan, and Turkmenistan,” said He, the author of the new study.
That trend is already shown by a 2019 locust outbreak in the southern part of the Arabian Peninsula, known as the Empty Quarter, which was “previously unsuitable for breeding due to vegetation conditions,” he said. “Similarly, Kenya, which had limited locust invasion areas between 1985 and 2002, has since become one of the most severely affected countries from 2003 to 2020.”
French researcher Cyril Piou, who has been working on locust control for about 20 years, said global warming adds a new twist to the ancient story of locust plagues. He was not an author of the new paper, and he said the study would have benefited from more local input.
“This is a species that was mentioned in the Old Testament,” he said, adding that improved management and control of locust swarms has reduced the impacts of outbreaks in recent decades. Before that, there were large outbreaks regularly affecting Eastern Africa, Western Africa and India, “with many years of swarms crawling from country to country, before the 1960s,” he said.
The new paper doesn’t seem to account adequately for those improvements in pest control efforts, which could affect the projections, he said, adding that he was “a bit sad” that the authors of the new paper didn’t collaborate more with people on the ground in the affected countries.
“There are many scientists in these countries that actually know a lot about locust ecology and management,” he said. “And they could have gotten some grasp of this information to avoid arriving at conclusions … without knowing what’s happening already on the ground.”
Human Factors Are Also Important
Many scientists agree that climate change “has the potential to produce more frequent outbreaks, bigger swarms (of locusts), and widespread food insecurity,” entomologist Jody Greene wrote in a 2022 blog post for Entomology Today. But she cautioned that warming is only one factor in a complex equation, and that human actions are equally important.
“The desert locust crisis is less about the insect and more about conflict and insecurity among people,” she wrote. “It is a story that demonstrates what can happen when countries do not coordinate enough among one another.”
Surveillance, emergency funding, new technologies, weather information, geographic information systems and historical records all have to be shared to inform regionally cooperative, proactive locust control measures to achieve locust-free conditions, she wrote.
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In fact, the outbreak from 2019 to 2022 started when unusual rains in the Empty Quarter fueled breeding that was not noticed, and “thus left uncontrolled,” said locust expert Robert Cheke, an entomologist and ornithologist with the United Kingdom Natural Resources Institute.
“Some moved to Pakistan and Iran where the monsoon season was longer than usual,” he said. Others migrated to Yemen and Somalia, where regional conflicts prevented some monitoring and control efforts, which further spurred the outbreak.
Piou said if rainfall increases in desert areas, there is a higher chance of desert locust outbreaks. But projections for rainfall in a warming climate aren’t made at a scale detailed enough to help much with projecting those events.
“Rainfall patterns are very hard to predict,” he said. A scarcity of weather stations in many of the areas affected by locusts adds even more uncertainty.
“Saying we are going to see a large increase of desert locust outbreaks at the end of the century, that, for me, is a bit dangerous to say,” he said.
Bob Berwyn
Reporter, Austria
Bob Berwyn an Austria-based reporter who has covered climate science and international climate policy for more than a decade. Previously, he reported on the environment, endangered species and public lands for several Colorado newspapers, and also worked as editor and assistant editor at community newspapers in the Colorado Rockies.
