Africa is currently experiencing the worst outbreak of locusts in decades. The insects are threatening the food supply for the continent, and there is no end in sight.

Desert locusts are to blame, and they are the most destructive of all known locust species. A combination of rapid growth and large appetites makes them especially troublesome. A recent swarm in Kenya was estimated to contain 100-200 billion locusts. As each locust can eat its own weight in food every day, that all adds up to the swarm devouring as much food as 84 million people every day.

Keith Cressman, senior locust forecasting officer at the FAO, recently returned from northeast Somalia and reports that the locusts are like “a moving carpet of yellow and black objects” each behaving the same way, and packed together so densely that you can’t even see the ground below them.

The insects have already destroyed hundreds and thousands of acres of crops in East Africa, and the UN is calling for international help to quell the crisis. They fear the numbers could grow 500 times by June and reach 30 different countries.

Several factors caused the massive outbreak. In May 2018, a cyclone hit the desert “empty quarter” of Oman, Yemen, and Saudi Arabia. After the unusual rainfall, vegetation flourished, and the well-fed locusts increased their population 400-fold over 6 months. Normally, the populations would shrink when plants die after the desert dries out again, and timely control efforts can prevent populations from booming.

In this case, however, a second cyclone hit in October 2018 and the population continued to increase—an estimated 8000-fold by March 2019. The locusts headed to southern Iran, crossing territory that hadn’t seen the insects in 50 years, and moved east into India and Pakistan. Last summer, many flew south with prevailing winds into Yemen, where civil war prevented any spraying of pesticides. The swarms moved to Ethiopia and Somalia in October 2019.

Compounding the problem, yet another cyclone unexpectedly hit the Horn of Africa in December 2019 and more breeding ensued. By the end of that month, growing swarms had entered Kenya. They reached Uganda and Tanzania in the past few days.

The next generation of locusts is now maturing and could devastate crops planted at the end of March if action isn’t taken rapidly. “We have a short window of opportunity to act,” Dominique Burgeon, director of emergencies at the Food and Agriculture Organization of the United Nations (FAO), said at a briefing Monday in New York City.

Tackling large locust swarms is challenging and requires fast-acting chemical pesticides sprayed from aircraft. Ethiopia and Kenya are now spraying those chemicals. Although the pesticides break down within 1 day, villages must be warned to temporarily move their livestock.

In Somalia, which has large grazing areas, FAO is instead helping the country use biopesticides. They consist of spores of the fungus Metarhizium acridum, which produces a toxin that kills only locusts and related grasshoppers. Since the last major locust outbreak in Africa, in 2003–05, researchers have been able to make the biopesticide cheaper, more effective, longer lasting in the desert, and easier to store.

“Large-scale use [of fungus] to control an invasion of desert locusts would be a first,” says Michel Lecoq, a retired entomologist who worked on locust control at the French Agricultural Research Center for International Development. “If successful, it will be a big step forward.”

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