- An infestation of fall armyworm has spread rapidly across Africa since it first appeared on the continent in 2016; it’s now been reported in 44 countries, with 80 different types of crops affected.
- For farmers and policymakers, the go-to solution has been to spray crops with pesticides, but researchers have warned of harm to farmers from unsafe use of the pesticides, as well as impacts on other insects that would otherwise keep the pests in check.
- Researchers have suggested a biocontrol solution — releasing large numbers of a wasp species known to infest fall armyworm eggs — but doubts remain about how effective it will be in a region with small farms and high crop diversity.
- There are also calls for better agronomic practices, such as more regular weeding of farms and crop rotation, to deny the pest a year-round supply of its preferred food.
Early one morning in April 2017, Anne Anyole found strange caterpillars feeding on her maize crop. At first she thought it was stalk borer, a pest familiar to farmers in western Kenya’s Kakamega county, especially when the weather is dry.
Maize is usually planted in March during the onset of the long rains that usually continue into August. But in 2017, it was still dry until early April, and the maize was still low to the ground, barely knee height.
Anyole went to the local agrovet, as rural shops supplying agriculture and veterinary products are known in Kenya. They sold her a pesticide commonly used in spraying vegetable pests. Anyole doesn’t usually use pesticides on her farm. She plants maize in March and then weeds it diligently until it’s ready to harvest four or five months later.
The caterpillars disappeared after she sprayed her field, but reappeared two or three days later. It was fall armyworm (Spodoptera frugiperda).
“I realized that the damage to the crops was increasing and more devastating than ever,” Anyole said. That year, farmers across Kakamega county turned desperately to every alternative, including spraying their crops with laundry detergent and painstakingly picking worms off their crops by hand and crushing them, but nothing proved effective.
“Since 2017, I have been harvesting low yields,” Anyole says. “I cannot get surplus to sell and pay school fees for my kids as it is my main source of income.” Where she says she would have harvested 800 kilograms (1,760 pounds) of maize after each of Kenya’s two growing seasons, her fields have yielded barely 250 kilos (550 pounds) per season since the armyworm appeared.
 Fall armyworm (Spodoptera frugiperda). Image courtesy G. Goergen/IITA via Flickr (CC-NC-SA-2.0) |
FAW made its first appearance in Africa in Nigeria in 2016. Scientists have not yet established how it reached the continent from Latin America, but once it arrived, it spread rapidly. S. frugiperda moths can migrate more than 500 kilometers (300 miles) before mating and laying their eggs — and can fly much longer distances with favorable winds.
In an alarmingly short span of time, the pest spread from West Africa to Southern Africa and then into East Africa. It has now been reported in 44 countries with infestations affecting 80 different crops.
“There was a lot of panic by farmers and governments,” says MaryLucy Oronje, a specialist in insects and crop production at the Centre for Agriculture and Bioscience International (CABI).
Across the continent, governments urged farmers to protect their crops by spraying them with insecticides. In Rwanda and Zambia, soldiers were deployed to spray maize fields in the fight against FAW.
“Most of the insecticides that have been used against FAW are not specific to armyworm, but are broad spectrum chemicals,” Oronje told Mongabay. “They will also kill off bees and other beneficial insects, such as predators and parasitoids that reduce insect pest populations and benefit indirectly as they help reduce other insect pest populations.”
Marc Kenis, head of risk analysis and invasion ecology at CABI, says that the problem of using insecticides is exacerbated by the fact that many smallholders do not protect themselves adequately when using insecticides, or else use banned insecticides.
Kenis told Mongabay that insecticides could also affect natural enemies of the FAW and other pests on farm, which may favor the emergence of secondary pests and oblige farmers to use more and more insecticides.
Oronje adds, “It’s possible that other animals are also affected and will continue to be affected by these insecticides. The extensive use of pesticides in Africa will later have impacts on biodiversity.”
She told Mongabay that no studies have been carried out to evaluate the impact on farmers themselves of the heavy use of insecticides since FAW’s appearance, but she worries that few smallholders know how to use these toxic chemicals safely or have the right protective equipment.
Kenis is among the researchers looking for ways to control fall armyworm that will be both cheaper and less risky to human health and the environment than hugely increased insecticide use. One such solution is what is known as biological control, in this case attacking fall armyworm with another species. This can be done either by introducing a new predatory species or by stimulating local populations of natural enemies.
Earlier this year, Kenis was the lead author of a study published in the April 2019 issue of the journal Insects, which announced that at least one natural predator of fall armyworm is already present in Africa. Telenomus remus is a tiny black wasp with a shiny body less than a millimeter long. It injects its eggs into fall armyworm eggs, where they develop into tiny white larvae barely visible to the naked eye. These larvae may be small, but they have a big appetite: they eat their hosts, and an adult wasp emerges instead of an armyworm caterpillar.
Kenis says deploying T. remus or another local parasitoid against fall armyworm poses hardly any risk.
“There is no health risk since a parasitoid cannot harm humans. The environmental risk is also limited since T. remus already occurs in Africa and has already found its place in the ecosystem,” he says.
There’s a catch, though: some predatory insects of this type naturally reach high levels of parasitism (sometimes above 50 percent), but studies of T. remus in the Americas have found the parasitoid is not an effective biocontrol agent by itself, says Kenis, because its natural parasitism rates are very low.
Deploying the tiny wasps as an effective biological control would involve breeding batches of hundreds of thousands of them on cardboard trays of FAW eggs, and releasing them into afflicted fields as they hatch. In the Americas, this method has achieved parasitism rates of greater than 90 percent.
“We can hope that in Africa, they may be able to do the same, thus inflicting high mortality in each FAW generation, which T. remus cannot do,” Kenis says.
The main challenge for using T. remus will be to find cost-effective methods to deploy it in the field. It has been used successfully in large-scale commercial operations in Mexico and the Bahamas to protect high-value vegetable crops grown in relatively small areas. Effectively controlling fall armyworm across much larger areas will be difficult, says Kenis: “But we hope to find very cheap ways to produce T. remus which could make it affordable as well for smallholders.”
Frederic Baudron, a senior scientist and systems agronomist from International Maize and Wheat Improvement Centre-CIMMYT Zimbabwe, is skeptical. “When an exotic pest is introduced to a new continent, it generally comes without its suite of natural enemies (think of the massive rabbit problem in Australia for example). It takes time for local natural enemies to control the pest (and doesn’t always happen). In addition, compared to the Americas, African agriculture is characterized by its very low input use, small farms, high diversity and high heterogeneity. Most solutions are thus not transferable,” Baudron says.
He tells Mongabay that biocontrol is not the focus of most interventions in Africa. There are calls for better agronomic practices such as more regular weeding of farms and crop rotation, to deny the pest a year-round supply of its preferred food, but as fall armyworm spreads rapidly, most interventions in the continent have turned to pesticides — for farmers and policymakers alike, it feels like a familiar and decisive intervention, despite the cost.
“This year, cases of FAW in Kenya, for example, are expected to be higher because of the delay in onset of rainfall, different planting times by farmers and high temperatures recorded this year,” Oronje says. The warmer the weather, the faster fall armyworm passes through its life cycle. Infestations have been recorded across the western part of the country where maize is a popular crop; the extent of the damage will only be assessed after September’s harvest has been tallied.
“There is a need to make scientific decisions on the risks of biocontrols and ensure that it only kills FAW,” Oronje says. “African governments need to hasten trials because the increasing temperatures will escalate the reproduction of FAW.
“We hope that this is something that can be upscaled after approvals from governments,” she adds.
As research into biological controls and other environmentally friendly solutions continues, Oronje says there will need to be increased education for farmers and agricultural extension officers about which insecticides work best, and how to use them safely.
“The consensus in the continent is that a combination of these three approaches — pesticides, biocontrol and agronomic practices — will be required to effectively control FAW,” Baudron says.
Banner image: Field inspection for fall armyworm in Kakamega County, Kenya. Image by Gilbert Nakweya for Mongabay.
Citation
Kenis, M., Du Plessis, H., Van den Berg, J., Ba, M. N., Goergen, G., Kwadjo, K. E., … Polaszek, A. (2019). Telenomus remus, a candidate parasitoid for the biological control of Spodoptera frugiperda in Africa, is already present on the continent. Insects, 10(4), 92. doi:10.3390/insects10040092
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