March of the Armyworm
Across Africa, a new invasive pest is damaging crops at an alarming rate – and it might soon go global.
Mohamud Abdu stands tall in his maize field in Alaba, Ethiopia, a small agricultural district over 200 kilometers south of the country’s capital, Addis Ababa. Smooth green leaves reach up to his waist. The field is off a dirt road where children ride old bicycles and the occasional wooden cart, pulled by donkeys and piled high with people, passes by.
photo Stephanie Parker
The sea of green where Abdu stands looks lush and healthy at first glance. The maize stalks are planted closely together and the leaves rustle gently in the wind. But upon inspection, these leaves are riddled with holes and plant detritus litter the remainder. Abdu pries open the whorl of a nearby maize plant with his fingers, and takes out a small caterpillar, roughly an inch long. It squirms on his palm.
“At first I tried handpicking the worms,” he says through a translator, explaining how he would go from plant to plant to pick off the caterpillars and squish them between his fingers. “But then I saw that they had returned. The problem was out of control.”
When Abdu first noticed the extent of the damage, he went to the local agricultural office, which gave him chemical pesticides. But, he says, the pesticides did not work. He even took the worm in his hand and sprayed it directly with the pesticide and says that still did not kill it.
That’s because the caterpillar munching its way through Abdu’s two-hectare farmland was the fall armyworm, a voracious crop pest that is native to the Americas but is a new arrival on the African continent. In the summer of 2017, Abdu says at least 50 percent of his maize crop was damaged by these worms that are wreaking havoc across farmlands in sub-Saharan Africa and posing a major threat to food security on the continent. And agricultural experts worry that it is a matter of when, not if, it will spread to the Middle East, Europe, and Asia. In other words – the rest of the world.
The fall armyworm is so named because of the way it marches through crops en masse during late summer and autumn in the Americas. Its scientific name, Spodoptera frugiperda, refers to the grey-patterned wings of the fall armyworm moth and the caterpillar’s penchant for destroying fruits (“frugiperda” is Latin for “lost fruit”). African farmers have long had to deal with infestations of the native African armyworm, Spodoptera exempta, which tend to cause serious damage to crops during rainy seasons or after periods of prolonged drought.
Native to tropical and subtropical regions of the Americas, the fall armyworm was first found and identified on the African continent in Nigeria in January 2016. Since then, it has been marching east and south through Africa like, well, an army.
It’s not clear how or when exactly this pest arrived in Africa. Some scientists think the caterpillar or its eggs may have reached the continent via imported produce. But it is also possible that it accidentally boarded a commercial flight. The insect reproduces quickly, with a lifecycle of 30 to 90 days, depending on the climate, and is a strong flyer, with adult moths covering up to 100 kilometers a night, even more if there is a strong wind. The longest recorded fall armyworm flight was 1,600 kilometers from Mississippi to southern Canada in 30 hours.
Either way, within a year the fall armyworm spread rapidly across the continent – as far east as Somalia and as far south as South Africa, and even to the island nations of Madagascar and Cape Verde. The United Nations’ Food and Agriculture Organization (FAO) says that by February this year, only 10 out of 54 African states had not reported infestation and that the pest is on the brink of causing devastating food shortages, especially in southern African countries that are recovering from a severe drought and are already deeply food insecure.
The fall armyworm feeds on over 80 different plant species that include rice, sorghum, and millet, but it especially likes maize, a staple crop that is the main food source of more than 300 million Africans. Unlike other larval pests, the fall armyworm doesn’t just eat the leaves or the fruit of a plant; it bores into the stalks as well, damaging the crops from both inside and out. There are other reasons – including the moth’s strong flying powers, the highly fertile adult female moth’s ability to lay more than 1,000 eggs in its 10-day life, and its tendency to develop pesticide resistance – that make it hard to keep this pest in check. Its inability to survive in cold temperatures is one of the key things that has helped keep the fall armyworm under control in most of the United States. In Brazil, however, where the warmer weather allows fall armyworms to breed all year round, it costs about $600 million a year to control them. Africa’s temperatures remain high all year long as well, and that has allowed the pest to proliferate faster than the continent’s mostly subsistence farmers can handle.
While climate change is a common culprit when it comes to agricultural problems, experts seem to agree that this is more of a globalization problem than a climate one. Africa’s climates were already ideal for the fall armyworm. However, while climate change hasn’t impacted the fall armyworm’s spread, it may have an effect on its level of damage. “To me, the most important factor is the double whammy of the stressed plants due to erratic rains, which could be due to climate change, and the fall armyworm, which can really reduce yields,” says Allan Hruska, FAO’s principal technical coordinator for fall armyworm.
The US Agency for International Development (USAID) reports that the pest may have cost up to $13 billion in crop losses in Africa so far. But it is still not clear exactly how much damage the fall armyworm is causing. For instance, the nonprofit Centre for Agriculture and Bioscience International (CABI) did surveys in Ghana and Zambia and those farmers reported on average around a 45 percent crop loss. However, because this is a new pest, it is possible they were overestimating the damage at the time.
“If we were losing that amount continentally, we’d already be in famine I think,” says Roger Day, program executive for CABI’s Action on Invasives program. “My estimate based on that logic is that the losses must be somewhat lower.”
photo Stephanie Parker
Hruska estimates the average loss to be closer to around 10 to 20 percent, but notes that individual farmers may see higher numbers, especially if their plants are already weakened to begin with. “We still don’t know how much yield loss is caused by the fall armyworm. And it’s not just yield loss but who is losing the yield. Even a 10 to 20 percent yield loss to smallholder farmers is a big deal because it’s their food security, not cash sales. These are subsistence farmers, and the majority of the maize they grow is for personal consumption.”
The fall armyworm is just one of the latest in a long line of agricultural pests invading new areas of the world. Thanks to increased travel and global trade, species are able to cross oceans at speeds and with frequency that would have been impossible only centuries ago. “Everything is moving around much more and that automatically increases the risk of pests being moved around,” Day says.
In 2006, for example, another American pest made its way across the Atlantic, landing in Spain. Tuta absoluta, known as the South American tomato leafminer, then found its way to Africa. The insect is a voracious tomato pest – in 2016, the term “tomato Ebola” was coined due to its toll on Nigerian tomato crops. Already it is in continental Europe, most of Africa, the Middle East, and now Asia as well.
Another invasive agricultural pest getting a fair amount of media attention went from east to west. Coffee rust, Hemileia vastatrix, is a fungus native to Ethiopia. In the late 1800s, it found its way to Ceylon, modern day Sri Lanka, and toppled the country’s coffee growing market. Around 100 years later, it showed up in Brazil and within a decade had spread throughout South and Central America’s coffee growing regions. It lay dormant for the next 30 years, but in 2012, it experienced resurgence and heavily disabled the Central American coffee growing industry.
“When you move a species to someplace new without its natural predators to keep it in check, it can become invasive,” Day says. Species often co-evolve, meaning that in the Americas, the fall armyworm has had predators evolving alongside it over thousands of years. But when it made the journey to Africa, it went alone, leaving its natural enemies behind. And once an invasive species is established, eradication is often no longer an option; the only hope is to reach a point of managed stasis where the pest is well-enough controlled that it cannot cause an undue level of damage.
That is where we are with the fall armyworm, and the focus of governments, agricultural scientists, and aid organizations has now turned towards management. First stop: chemical pesticides.
While a problem on the scale of the fall armyworm will likely take years to manage, farmers and governments looking for a quick, interim solution more often than not rely on chemicals. “The immediate reaction on the part of national governments is to go to pesticides,” Hruska explains. “There’s political pressure to do something immediately … Donors give money to governments and they buy pesticides and either give them away [to farmers] or apply them [on the fields] themselves.”
photo courtesy of Food and Agriculture Organization
However, even as an interim measure, this is a flawed option. First, most African farmers are smallholders who can’t afford a regular supply of pesticides, and government handouts last only so long. Then there’s the issue of the pesticides themselves. The fall armyworm has already developed resistance to many pesticides in its native range. Besides, most locally available pesticides tend to be broad-spectrum ones that don’t necessarily work on the fall armyworm. To compound the problem, even these are sometimes mislabeled, highly toxic chemicals that can prove hazardous not only to the environment but to the farmer and the farmer’s family as well.
“In some cases you’re getting really hazardous materials into the hands of farmers who have never really used these things before,” says Hruska. “So the exposure can be quite high due to the lack of experience and lack of knowledge about these substances.”
Unlike in the United States, where maize is planted in neat rows and giant spraying machines can cover fields in precise amounts of pesticide, maize in Africa is usually planted close together, more haphazardly. It grows up to about six feet tall. With just the backpack sprayers that most of these farmers use, caterpillars at the top of the plants are very difficult to reach.
Alongside the smattering of unverified pesticides, African farmers are also resorting to more traditional control methods such as handpicking the armyworms one by one and applying ash, sand, salt, or soil into the whorl of the maize plant to suffocate the caterpillar. Some farmers are spreading lard on young maize stalks to attract ants up the stems to eat the fall armyworm larvae. Others are using a mixture of sugar and fish soup to attract ants or applying crushed neem leaves, which contain the insect repelling chemical azadirachtin.
Hruska sees these indigenous practices as important tools in the fight against the pest. He says that the FAO is encouraging farmers to explore and study local practices, because some of them are effective, and some are “effective enough.”
“These practices might sound primitive, but they are locally available and almost free and, in some cases, they cause a high percentage of mortality among fall armyworm,” he says. “If there’s 10 to 20 percent yield loss from the fall armyworm, and if ash can halve that amount, that may be enough for [the farmers] to get by on.”
Some are not as convinced. BM Prasanna, director of the Global Maize program at the Mexico-based International Maize and Wheat Improvement Center, for instance, is more skeptical. “We keep hearing about indigenous-based practices but we need to test this,” he says. “How effective is this practice? How affordable is this practice? How widely available is this practice? Can we scale up this practice across the country, across the continent?”
Either way, everyone agrees that there is an urgent need to work out fast and effective ways to the stall the relentless march of the fall armyworm through Africa.
A few low buildings surrounded by test fields of millet and sorghum and insect traps that look like phone booths make up the National Institute for Agronomic Research of Niger. The research center in Maradi, Niger’s third largest city, sits an hour’s drive from the country’s border with Nigeria. Inside the lab, air conditioners work valiantly against the heat and intermittent power failures. Amid glass cages and petri dishes, doctoral student Laouali Amadou works to figure out biological control solutions to the fall armyworm invasion.
Amadou had been working on biological control for two millet pests – the pearl millet headminer and stemborer – but with the recent arrival of the fall armyworm in Niger, a deeply food insecure country that was ranked 187 out of 188 countries on the UN’s 2015 Human Development Index, he expanded his research to biological control agents for the caterpillar.
Amadou has identified some locally available biological agents that show promise in controlling fall armyworm. One of these is Habrobracon hebetor, a tiny wasp that is a larval parasitoid, meaning it will predate on insects in the larval/caterpillar stage. This wasp is effective at killing young headminer larvae and has potential to do the same to fall armyworms. “We have seen that the Habrobracon hebetor can kill the [armyworm] larvae and it can lay eggs on the laboratory level,” Amadou says. The few field tests that Amadou and his team have run so far are showing some positive results too, but the rate at which the wasp kills the armyworm is lower than in the laboratory setting.
Other parasitoids with potential include Trichogramma, a small wasp that feeds on insect eggs, which has native sub-species spread across the world. In Brazil, Trichogramma wasps are used as part of the country’s overall pest control strategy. However, the fall armyworm egg clusters, which look like a small, white droplet of spit, are protected by tiny scales, which Trichogramma can have difficulty penetrating.
“Parasitoids and their hosts co-evolve together,” says FAO’s Hruska. “Those niches haven’t yet been filled in Africa, so there’s less natural control of fall armyworm in Africa than in the Americas.” A popular strategy to combat this is to import the pest’s natural enemies. Researchers are, for instance, considering using Telenomus remus, another egg parasitoid native to Papua New Guinea that is currently being used to help control the fall armyworm in Florida. At least a dozen Telenomus species can presently be found across Africa, and Amadou has also found a species of Telenomus attacking fall armyworm eggs, but has not yet identified which one. Of course, bringing in these enemies could cause other problems. “There’s a touch of irony in that area,” CABI’s Day says, “because the problem is invasive species and the solution is to bring in another exotic.”
Crop scientists are also exploring a number of alternative control strategies, including building plant resistance through crossbreeding and using genetically modified corn.
Researchers have yet to find a single solution that’s effective against this pest.
Robert Beiriger, a senior biological scientist specializing in plant breeding at the Everglades Research and Education Center, has been working for the past decade on hardier plant hybrids that can survive armyworm attacks. He has been working on managing the fall armyworm in Florida for nearly 30 years and is also working with scientists on the pest in Africa. “We’ve got the corn out in the field growing now and I am hopeful we may have some test hybrids to send to Africa this fall,” Beiriger says.
Bt (Bacillus thuringiensis) transgenic corn is used heavily in Brazil and the United States, but the fall armyworm has also evolved resistance to some Bt toxins as well. Besides, on the African continent, South Africa is the only country that even permits GMO crops to be grown, making Bt maize untenable in most of the continent.
Beyond the regulations, it is hard to imagine how smallholder farmers who often cannot afford basic agricultural inputs would be able to afford modified seeds. “Even if it’s approved, not every farmer can afford it,” says Muni Muniappan, director of the USAID-funded Feed the Future Innovation Lab for Integrated Pest Management (and, full disclosure, my former boss). “And one variety might not be suitable all over the continent. The pest doesn’t just attack corn; it attacks others crops.”
Researchers are also exploring integrated pest management techniques, an economic and environmentally sensitive approach that relies on a combination of common-sense practices – such as using biopesticides made of plant extracts, insect pathogens like fungi, viruses, and bacteria, natural pest predators like wasps and ladybugs, and intercropping fields with plants that repel pests. These techniques do not necessarily totally eliminate pests, but can help keep their populations, as the FAO puts it, “below the economic injury level,” while minimizing risks to human health, beneficial and non-target organisms, and the environment.
“Interestingly, some of the traditional cropping systems farmers use are already more resilient in that sense,” Day says, pointing to a push-pull intercropping system that’s used by some farmers in Africa. In this system, maize is planted alongside Desmodium, a legume that repels certain pests. The edge of the maize field is then lined with Napier grass, which attracts the pests away from the maize. Researchers have found that fall armyworm infestation is 80 percent lower in plots in where push-pull has been adopted.
“There is no single technology that is ideal against fall armyworm,” says CIMMYT’s Prasanna. “If you want to sustainably manage or control this pest you need to adopt a broad range of tools.”
While the Sahara has thus far provided a barrier against the fall armyworm traveling north, it is only a matter of time until it turns up in Egypt and from there, it’s an easy flight to other parts of North Africa, the Middle East, and eventually, Europe and Asia. Already, the fall armyworm is in Sudan’s Nile valley.
“Bioclimatic models won’t show Egypt as a suitable place and in the desert, corn won’t grow,” Muniappan says. “But it doesn’t take the Nile into account and on either side of the river, there is agriculture and there is corn growing there.”
The FAO is planning a workshop on fall armyworm in Egypt in next few months to train Egyptian officials, farmers, and plant doctors – local experts trained to help farmers – and USAID is offering prize money for digital tools that help farmers obtain information and make management decisions. And in a clear indication that countries outside of Africa recognize that this is a global problem, the European Food Safety Authority has produced an urgent pest categorization for the fall armyworm and is working on a full risk assessment for the continent that should be ready this summer.
Meanwhile, for the tens of thousands of small farmers like Abdu whose fields have already been invaded, there’s no quick solution at hand. It will take a host of strategies to control this pest, and Abdu and farmers like him, having no other option, will continue to plant maize and wait.
Stephanie Parker is a freelance environmental writer and photographer living in Switzerland.