A locust plague hit East Africa. The pesticide solution may have dire consequences.

Heavy use of a broad-spectrum pesticide seems to have slowed the desert locust invasion. What the repercussions of that approach are isn’t yet clear.

Seen from the air at dawn, a swarm of desert locusts begins to move across farmland toward the forests of Mount Kenya.

A swarm of locusts is awe inspiring and terrible. It begins as a dark smudge on the horizon, then a gathering darkness. A rustle becomes a clatter that crescendos as tens of millions of voracious, finger-sized, bright yellow insects descend on the land. Since late 2019, vast clouds of locusts have shrouded the Horn of Africa, devouring crops and pastureland—and triggering an operation of staggering proportions to track and kill them.

So far, a ground and air spraying campaign over eight East African countries, coordinated by the United Nations Food and Agriculture Organization (FAO), has staved off the worst—the very real prospect that the locusts would destroy the food supply for millions of people. Last year, the operation protected enough pastureland and food stocks, by the FAO’s calculations, to feed 28 million people in the Greater Horn of Africa and Yemen for an entire year.

But progress comes with yet-unknown consequences to the landscape, and responders have sought to find the elusive balance between eradicating the invading pests without destroying foliage and harming insects, wildlife, and humans. Northern Kenya is renowned worldwide for its bee diversity, and farmers and conservationists worry that bees are becoming casualties.

So far, 475,000 gallons (1.8 million liters) of chemical pesticides have been sprayed over 4.35 million acres (1.76 million hectares) at a cost the FAO says is $118 million. The spraying is expected to continue this year.

Assessments of possible environmental damage are incomplete at best, though the effects of pesticides have been well documented for decades in other settings. Broad spectrum pesticides are not only very effective at killing locusts, they also kill bees and other insects. They leach into water systems and can damage human health.  

“Of course, there is collateral damage,” says Dino Martins, an entomologist and executive director of the Mpala Research Center in Kenya. “All these chemicals are designed to kill insects and they do so in very large numbers.”

Caught off guard

Kenya had not suffered a major locust invasion in 70 years. When the first swarms arrived in 2019, the country was woefully unprepared for what had been, quite reasonably, regarded as a remote threat.

“They had no equipment, no expertise, no pesticides, no aircraft, no knowledge,” says Keith Cressman, the FAO’s senior locust forecaster.

The swarms began forming in 2018 after cyclones dumped heavy rain on the inhospitable deserts of Arabia, allowing locusts to breed unseen in the wet sands. Strong winds in 2019 blew the growing swarms into Yemen’s inaccessible conflict zones, then across the Red Sea into Somalia, Ethiopia, and Kenya.

In the early stages of the locust control effort Kenya threw everything it had at the problem. “It was a panic reaction,” says James Everts, a Dutch ecotoxicologist specializing in the environmental effects of pesticide use.

The spraying continued even as the COVID-19 pandemic spread and shuttered much of the world. Donning face masks against the coronavirus, hundreds of local volunteers, as well as members of Kenya’s National Youth Service, shouldered knapsack sprayers and, with minimal training, unloaded on the locusts with whatever pesticides happened to be in stock. They sprayed tens of thousands of liters of deltamethrin, as well as hundreds of liters of fipronil, chlorpyrifos, and other insecticides, many of which are banned in Europe and parts of the United States.

In one documented case in the northern region of Samburu, a ground control team sprayed 34 times the recommended dose of pesticide on a patch of ground, killing bees and beetles while spilling pesticide on themselves and crops.

“In the beginning it was an emergency,” says Thecla Mutia, who leads an FAO team monitoring the environmental effects of locust-control efforts in Kenya. “The whole idea was to manage this as fast as possible to ensure food security.”

The FAO says, however, that it did not approve the use of volunteers in the campaign nor the spraying of pesticides not recommended for locust control.

Pesticides banned in Europe and the U.S.

Designed to kill, pesticides are toxic by definition, but they are also blunt weapons. Three of the four chemicals recommended by the FAO and authorized by regional governments—chlorpyrifos, fenitrothion, and malathion—are broad-spectrum organophosphates, widely used pesticides sometimes referred to as “junior-strength nerve agents” because of their kinship to Sarin gas. The other, deltamethrin, is a synthetic pyrethroid, which is especially toxic to bees and fish, though much less so to mammals.

The FAO’s Pesticides Referee Group, which vets pesticides for use in locust control, lists all four chemicals as high risk to bees, low or medium risk to birds, and medium or high risk to locusts’ natural enemies and soil insects, such as ants and termites.

The European Union banned chlorpyrifos early last year, and in the U.S. state bans have been enforced in New York, California, and Hawaii. Fenitrothion, too, is banned in Europe, but permitted in the U.S. and in Australia, where the government deploys it as a central weapon in the fight against locusts.

“We are not hiding what conventional pesticides are,” says Cyril Ferrand, FAO resilience team leader in Nairobi, who points out that doing nothing was not an option in the face of the rapidly expanding swarms. “We want to lower the population of desert locusts in a way that is responsible.”

Non-toxic alternatives

Non-toxic biological alternatives that kill locusts, but do no other harm, have been available for decades. Yet chemical pesticides remain the weapon of choice, accounting for 90 percent of the spraying in the current East Africa campaign.

Biopesticide development began in the late 1980s after the end of a years-long locust plague that stretched from North Africa to India.

“When we saw the figures of the millions of liters of pesticide being sprayed, even the donor community was horrified,” recalls Christiaan Kooyman, a Dutch scientist who developed the biopesticide using a fungus, Metarhizium acridum, that attacks locusts. “And they asked the scientists, ‘Is there nothing else we can do?’”

Metarhizium, which has been on the market since 1998, is recommended by the FAO as the “most appropriate control option” for locusts, yet is rarely used. It is slow acting with a low “knockdown” rate—meaning it kills over days rather than hours. It is expensive and tricky to apply. And it is most effective against immature “hoppers,” rather than the adult swarms that are the greater threat.

Its best feature—that it kills only locusts—also makes it a less profitable product. Companies have little incentive to manufacture metarhizium and go through the costly bureaucratic process of registering it in a country until it is needed—and by then it is too late.

“Locusts aren’t around very much, and manufacturers are not keen on producing something that doesn’t get used,” says Graham Matthews, a British scientist and the founding chair of the Pesticides Referee Group. When the swarms arrive, “you don’t want to wait for production, you want it off-the-shelf,” he adds. 

Instead, governments reach for the broad-spectrum toxic chemicals mass-produced by large agrochemical companies.

Extent of harm is unknown

What makes widespread spraying of chemical pesticides especially worrisome to farmers, herders, scientists, and conservationists in Kenya is that so little is known about what, if any, harm the pesticides have done. A U.S. government environmental assessment of the regional locust operation warned of the “potential for significant adverse impacts on environment and human health,” and a review by the World Bank found the environmental risk to be “substantial.”

Yet more than a year into the control campaign, the FAO’s assessment of the environmental impact of the spraying has not been made public.

“The excessive use of pesticides is of course detrimental to biodiversity, but it has not really been quantified as to what the level of impact is,” says Sunday Ekesi, an entomologist and director of research and partnerships at the International Center of Insect Physiology and Ecology (ICIPE) in Nairobi, part of a government task force set up to tackle the desert locust invasion.

“Our key concern is the impact it has on the pollinators,” says Anne Maina, of the Biodiversity and Biosafety Association of Kenya. The farmers she works with attribute reduced honey and mango harvests to the disappearance of bees. Martins shares these concerns, but says the lack of monitoring information means it is impossible to know what’s really going on.

“Northern Kenya and the greater Horn of Africa is one of the world’s hotspots of bee diversity, with thousands of species, most of which we know absolutely nothing about,” he says. “We need to develop tools that allow us to both control locusts and protect the fragile biodiversity of the region’s drylands.”

The FAO’s 2003 guidelines on safety and environmental precautions acknowledge that aerial spraying may have less impact on human health than ground spraying, but often creates “more environmental concerns” because it risks contaminating ecologically sensitive areas. Aerial spraying increases the potential for “uncontrolled drift,” whereby chemicals—much like the locusts themselves—are blown off course by the wind.

Mutia, the FAO’s team leader for environmental monitoring, insists that ground-spraying teams have become better trained and local communities are better informed about the spraying and the risks to themselves and their livestock. Kenya’s overall locust operation today has improved since the early weeks of the invasion.

“Done right, the environmental impact is very low,” says Cressman.

A key report still under wraps

Still, Mutia’s environment and health monitoring report, finished last September, has yet to be made public. And there is confusion over why. The FAO says the report is for Kenya’s agriculture ministry to release, but a ministry spokeswoman says the FAO has yet to deliver it.

In an interview, Mutia says she found “no cause for alarm,” in her review of the spraying.

However, a copy of the report obtained by National Geographic paints a more detailed and problematic picture, with evidence of heavy overdosing at the Samburu site and widespread lack of communication with residents in sprayed areas.

In four of the 13 sites inspected, there was no sign of locust deaths at all, suggesting either that the spraying had been ineffective or that the monitoring teams weren’t in the right locations. The report says they were repeatedly given inadequate location information and lacked the helicopters and other vehicles required to quickly reach more remote sites.

“Our main concern has been the focus on control of the locusts without a parallel monitoring system of the undesired effects,” says Raphael Wahome, an animal scientist at the University of Nairobi. He says the FAO’s information should be made available to researchers and others: “Your guess is as good as mine as to what is happening wherever [the pesticides] have been used.”

Editor's note: The county in northern Kenya that was heavily sprayed was Samburu.

Editor's note: After this story was published, the FAO reviewed its data and provided updated numbers for the amount of pesticide sprayed, the area affected, and the cost. Those numbers have been incorporated into the article, along with the FAO's statement that it did not support the use of volunteers in the locust control campaign nor the use of pesticides not recommended for the purpose.

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