Locust Swarms Are Eating Their Way Across Two Continents

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Climate change is worsening the largest plague of the crop-killing insects in 50 years, threatening famine in Africa, the Middle East and the Indian subcontinent.

As giant swarms of locusts spread across East Africa, the Arabian Peninsula and the Middle East, devouring crops that feed millions of people, some scientists say global warming is contributing to proliferation of the destructive insects.

The largest locust swarms in more than 50 years have left subsistence farmers helpless to protect their fields and will spread misery throughout the region, said Robert Cheke, a biologist with the University of Greenwich Natural Resources Institute, who has helped lead international efforts to control insect pests in Africa.

“I’m concerned about the scale of devastation and the effect on human livelihoods,” Cheke said, adding that he also worried about “the impending famines.”
“Despite the coronavirus pandemic, the region needs money and equipment to deploy insect control teams in the affected regions,” he said.

New swarms are currently forming from Kenya to Iran, according to the the United Nations locust watch website. Addressing the outbreak requires urgent, additional funding and technical help from developed countries, Cheke said, because the tiny size and budget of the United Nation’s Food and Agricultural Organization team responsible for locust monitoring and control is already overwhelmed.

Changes in plant growth caused by higher carbon dioxide levels, as well as heat waves and tropical cyclones with intense rains, can lead to more prolific and unpredictable locust swarming, making it harder to prevent future outbreaks.

The desert locust (Schistocerca gregaria) needs moist soil to breed. When rains are especially heavy, populations of the usually solitary insects can explode. In Kenya, one of the biggest swarms detected last year was three times the size of New York City, according to a March 12 article in the journal Nature. Swarms a fraction of that size can hold between 4 billion and 8 billion locusts.

At times, the locusts in East Africa have swarmed so thick that they have prevented planes from taking off and their dead bodies have piled up high enough to stop trains on their tracks.

Global Warming’s Many Impacts on Insects

The changing climate has spurred other insect invasions. Warmer winters, for example, are magnifying an ongoing bark beetle outbreak in western North America. Until the 1980s, periodic cold snaps kept the beetles in check. But since then, the tree-killing bugs have swarmed—not as fast as desert locusts, but just as destructively. Since 2000, they’ve killed trees across about 150,000 square miles in Canada and the western U.S., an area nearly the size of California. In recent years, historic bark beetle outbreaks have also devastated European forests.

Other research shows that seasonal shifts caused by global warming are disrupting cycles of insect reproduction and plant pollination, including a recently documented decline of bumblebees, threatening food production in some areas.
Global warming is also affecting the feeding and breeding patterns of North America’s grasshoppers, species that behave similarly to locusts. In the 1930s, swarms of grasshoppers destroyed crops in the Midwest, even eating wooden farm tools and clothes that were drying outside. States like Colorado used flamethrowers and explosives to battle the insects.

It’s hard to predict how grasshoppers will respond to today’s changing climate, said University of Oklahoma biologist Ellen Welti, who studies the relationship between insects and plants.

But, she said, “Warmer winters, with less egg mortality and changes in precipitation patterns that affect the amount and quality of plant food, could lead to outbreaks of particular grasshopper species or other herbivorous insects.”

Locust outbreaks could be driven by changes in plant nutrients caused by extreme weather, Welti said, like more frequent soggy tropical storms, which make plants grow faster but dilute elements like nitrogen. “Locusts have a weird physiology—they like low nitrogen plants,” she said of connections she explored in a recent study published in the Proceedings of the National Academy of Sciences.  But the current locust outbreaks, Welti said, are occurring against the backdrop of an alarming global decline in overall insect abundance, which is also, to some degree, connected to climate change and will have far-reaching ecosystem impacts…

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