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Changing climate creates ideal conditions for devastating locust swarms

Mature desert locust. Image by Obi Anyadike/The New Humanitarian

Mature desert locust. Image by Obi Anyadike/The New Humanitarian

  • A second wave of locust swarms is spreading across the Horn of Africa, following an earlier swarm that devastated large areas at the end of 2019.
  • Increased rainfall and storm frequency have created conditions conducive to swarms of desert locusts.
  • Swarms are basically impossible to control once they form, and widespread aerial and ground spraying of insecticides risks damaging the environment.

Scientists, agricultural officers and farmers are struggling to protect crops from a fresh wave of desert locusts.

Earlier swarms overran the Horn of Africa region in December 2019, and the U.N.’s Food and Agriculture Organization (FAO) predicted a second wave would emerge. That second wave duly emerged in April, spreading across northeastern Kenya before moving into Uganda and South Sudan in May. These swarms are made up of the younger and more voracious offspring of the locust swarms that hit the region in December and January.

“This is not the first time that East Africa has seen locust upsurges approach this scale,” says Hamisi Williams, an FAO representative in Kenya, “but the size of the current situation is unprecedented in recent memory — sort of a 100-year storm.”

A swarm of desert locusts (Schistocerca gregaria), numbering anywhere between 10 million and 100 million individuals, can fly up to 150 kilometers (90 miles) a day. Swarms have been known to migrate to Ethiopia and Somalia from as far away as India. As they move, the females lay eggs, leaving behind the nuclei of successive swarms that emerge a few weeks later.

Williams says climate change, which has affected storms and rainfall patterns in this region, is an important driver of locust population dynamics. Over the past three years, more frequent Indian Ocean cyclones have played a role in increased numbers of locusts.

“In 2018, two cyclones dumped heavy rain on the uninhabited portion of the Arabian Peninsula known as ‘The Empty Quarter.’ There, locusts can breed and reproduce freely, undisturbed by humans. The locusts bred in the Empty Quarter for nine months, over three generations. That is the original source of the East Africa upsurge we are seeing now,” Williams told Mongabay.

These swarms can easily cross the narrow bodies of water that surround the Arabian Peninsula. They overflew the Red Sea, the Gulf of Aden, and the Arabian Sea to arrive in the Horn of Africa in 2019. There, says Williams, another spell of abnormally high rainfall in December 2019 triggered another spasm of reproduction.

Cyril Ferrand, head of the FAO Resilience Team East Africa, picks up the tale. “On Dec. 28, the swarms came in from Ethiopia and Somalia. The arid and semi-arid countries that they flew into were conducive for breeding, given the warm weather and moist soil caused by the heavy rains of 2019. These first generation ‘Kenyan born’ locusts grew [multiplied] 20 times, and their offspring would also grow 20 times larger, bringing the expected number of locusts from the original ones to 400 times bigger than the first which flew into the country.”

Locust swarm at Samburu, Kenya. Image by Sven Torfinn/FAO.
Locust swarm at Samburu, Kenya. Image by Sven Torfinn/FAO.

The insects have swarmed at a time when their preferred food is available in abundance in East Africa: rangeland blooming freshly green after rainfall and fields filled with new-planted crops.

National governments, the FAO and the Desert Locust Control Organization for Eastern Africa (DLCO-EA) are cooperating to control the locust swarm by spraying insecticide from the air. One DLCO-EA aircraft positioned at Lodwar, in northern Kenya, is conducting cross-border spraying over Uganda and South Sudan. But the global coronavirus pandemic has slowed the importation of pesticides and restricted movement of ground control personnel, says Stephen Njoka, the DLCO-EA director.

This second wave of locusts will deal a heavy blow to food security, according to Daniel Otaye, associate professor of plant pathology from the Department of Biological Sciences, Egerton University, Kenya.

Locusts are best controlled before they invade the farms; but once swarms do appear, Otaye says they can be diverted away from crops by growing other plants like Mexican marigolds (Tagetes erecta) around the edges of fields (as border crops). These “bait” plants attract the locusts, congregating them so they can more easily be sprayed with insecticide.

Farmers can also dig up locust eggs, which females lay just below the surface of the ground. “They lay about 50 eggs in a hole 5 centimeters [2 inches] below the ground, and cover them with a foam that looks like a sponge used for washing,” Otaye says. “When these are spotted, they are dug up with a hoe or plowed to bring eggs to the surface to expose them to the air. That way, the eggs dry up or are eaten by birds.”

In hot and dry conditions, this practice can reduce the insects’ population by 80-90%.

But the approach most widely used is the general spraying of insecticides across large areas. Kenyan environmentalists have warned that this will have harmful effects on the environment. “This looks like the magic bullet in that once vegetation is treated, the insects either go away or eat the plants and die. However, the pesticides being chemicals, their spread over large areas can be an environmental disaster. The harmful effect of chemical pesticides on the soils, groundwater and aquatic fauna is an issue,” Otaye says.

He says pesticides could also have devastating effects on beneficial insects, such as bees and ladybugs, as well as earthworms, damaging ecosystem health.

Scientists are collecting data to strengthen control measures, including through cellphone apps allowing people to report sightings of locusts as they spread across the region. Observer reports of the locusts’ life cycle are vital to choosing the right strategies at each moment.

“If they are immature (pink) we know they will not start laying eggs soon, and aerial spraying is best to use. If they are mature (yellow) the race is on to ensure that they do not start breeding. When they are spotted coupling, at this stage they do not fly and mainly concentrate on burying eggs before they die. At this point, the better strategy is to wait until the eggs start hatching and have the ground teams spray using hand-held sprayers,” Williams says.

Banner image: A mature desert locust. Image by Obi Anyadike/The New Humanitarian.

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