Fall armyworm Spodoptera frugiperda (Smith 1797) on damaged corn leafs with excrement ID 76957233 © Mikhail Kochiev | Dreamstime.com Fall armyworm Spodoptera frugiperda (J.E. Smith, 1797) on the damaged corn leafs with excrement
The fall armyworm has destroyed maize crops across more than 20 African countries © Mikhail Kochiev/Dreamstime

An invasion of fall armyworms from the Americas has ravaged crops across more than 20 African countries, putting hundreds of millions of people at risk of hunger.

Experts warned this week that the continent will struggle to contain the threat posed by the 3.4cm caterpillars that have no known effective predator.

“This is science fiction turned fact,” said Boddupalli Prasanna, a director at the International Maize and Wheat Improvement Center. “The fall armyworm is much more evil than other [pests] because I don’t think it can be eliminated. Meanwhile, the range of options available to tackle it are limited and the cost of these options is expensive.” 

The fall armyworm is native to the Americas and survives in temperatures above 10 degrees Celsius. It is named after the time of year it does most damage — autumn — and its feeding habits; after devouring a crop the whole “army” advances.

It feeds on 80 different plant species but the most prevalent strain eats maize, which is the staple of 200m people in sub-Saharan Africa. About 300,000 hectares across the region have already been ravaged.

Roger Day, at the Centre for Agriculture and Biosciences International, estimated the fall armyworm would cause damage worth about $3bn to Africa’s maize crop over the next 12 months.

Unless the insects advance is contained there is a risk of “further spread into Europe via the Mediterranean basin and Asia through the Middle East is almost certain”, the UN’s Food and Agriculture Organisation warned in a report. 

“The most likely scenario is that it’s going to spread both geographically and in intensity,” said Lewis Hove, a crop resilience expert at the FAO. “The infestation rate [in crops] is usually around 80 per cent but in some areas it is 100 per cent.” 

Scientists believe the fall armyworm arrived in Africa in a shipment of maize. It was first detected on the continent in west Africa in January 2016. A year later, it was in southern Africa and it has since swept north, with some moths flying up to 100km a day. It has recently been reported as far north as Ethiopia. 

Unless sprayed with effective insecticides quickly after initial detection, the fall armyworm becomes extremely hard to contain. 

Each adult moth lays up to 2,000 eggs during its two-week life, usually in batches of 100-200 on immature maize plants. Newly-hatched larvae often tunnel directly into maize before crawling to the ground to pupate. 

Michael Otiwi, a researcher at Uganda’s National Agricultural Research Organisation, said African farmers are becoming increasingly desperate as the insect proves resistant to most chemicals. 

“Recommended doses of insecticides are not sufficient so farmers are using double or even triple,” he said. “But these don’t work usually and pose serious issues for the safety of the users and the environment.” 

An extensive drought that has affected large swaths of sub-Saharan Africa for much of the last year has exacerbated the situation as it creates the prolonged hot, dry conditions in which the armyworm thrives. 

Experts at a conference of Nairobi this week said the only major crop that appeared to be able to resist the pest is cassava, probably because it produces cyanide. 

Joe DeVries, vice-president of the Alliance for a Green Revolution in Africa, said it was difficult to estimate the cost of trying to contain the fall armyworm in Africa, but added that the $600m Brazil spends on containment annually “is a good benchmark”. 

Mr Prasanna said the aim of the Nairobi conference was to find solutions to tackle the armyworm in both the short, medium and long term. Developing resistant strains of maize is likely to take at least four years, he said. 

One of the ways the US has been able to mitigate the armyworm’s impact is through the use of genetically-modified maize, but this is rarely planted in sub-Saharan Africa, where there is widespread opposition to such crops. 

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