Fear the fall: the armyworm that threatens food growers everywhere

The fall armyworm could be one of the most devastating threats to sub-Saharan African life that the continent has seen in generations. In addition, it could potentially spread across the world, damaging the livelihood of millions and threatening essential food sources.


The fall armyworm could be one of the most devastating threats to sub-Saharan African life that the continent has seen in generations. In addition, it could potentially spread across the world, damaging the livelihood of millions and threatening essential food sources.

This moth species has been a blight on the Americas, especially Brazil and other nearby South American countries, since 1957. When a caterpillar, these moths burrow into crops and eat them from the inside out. There are several varieties of the armyworm, or spodoptera genus, but the fall variety (spodoptera frugiperda) is the family that causes the most widespread damage.

The African armyworm and the fall

The first reports of the fall armyworm hitting Africa cropped up in January 2016, when the insect was found in Nigeria. It quickly spread to surrounding areas, including Togo and Benin. By May 2017, an estimated 26 African countries found fall populations, with several countries such as Rwanda having to mobilise their military to coordinate distribution of anti-pest measures.

Ghana’s agricultural minister recently asked for a state of national emergency to be declared as a result of spodoptera frugiperda’s impact. It was originally hoped that the pest would be contained in the vicinity of Nigeria, but it is a strong flier and dominant southern winds have spread the insect across southern Africa.

The African continent already had its own native pests such as Spodoptera exempta. There are a few important distinguishing features between the two genuses, most notably the Spodoptera has a penchant for maize, but only eats the leaves of the plant. This is still a significant issue, but is much easier for the farmer to spot and control.

However, the fall variety is concealed inside the corn, meaning farmers often cannot see the problem before it’s too late. It also means that the caterpillar is hidden away from any contact pesticides that might be used on the crop.

Professor Kenneth Wilson of the University of Lancaster Environment Centre is an expert on the interaction between parasites and their hosts. He has spent much of his career studying the African armyworm and methods of combatting the pest. He said: “In terms of the damage it might cause, it’s difficult to tell.

“It mainly attacks maize and sweetcorn. Once the reports start trickling in over the next few months, we’ll know the magnitude of the effect. My feeling is that there will be perhaps a 20% reduction in maize yield. That’s the sense I’m getting from talking to people.”

Maize occupies over 400 million hectares of growing space on the continent and is a staple food for millions.

Fighting a losing battle

Wilson also suggests many fall armyworm populations have developed resistances to many of the most common chemical pesticides due to their extensive use in the Americas, especially North America, and that: “it’s very likely that this new invader has come along with resistances to many of the used chemicals”. In addition, most farmers on the subcontinent cannot afford to import an expensive anti-pest measure.

"It mainly attacks maize and sweetcorn… my feeling is that there will be perhaps a 20% reduction in maize yield."

Other methods have been considered to combat the pest. In the Americas genetically modified (GM) crops such as Bt-corn are being used, which has been developed to have in-built measures to protect against pests and disease, such as producing a protein while growing that kills off lepidoptera larvae. However, concern is growing that the moth is also evolving to be resistent to the protein.

While Bt-corn is a short-term fix for the cereals market, this won’t be reassuring for other crop growers. The fall has been reported on more than 80 different host plants, including those of vital economic importance to the southern Africa region such as cotton and tobacco. The species has even been shown to be cannibalistic.

According to Wilson, one potential hope for crop growers is the cassava plant, which is grown extensively on the continent. Because cassava is cyanogenic, it’s possible the natural cyanide in the plant would kill off any fall caterpillars.

Wilson’s response has been to try and adapt a method he has been developing to combat African armyworm that uses a bacculovirus to control the population. He said: “One of the advantages of a bacculovirus is that it is inherently very genetically diverse. We know from our field sampling when researching for the African armyworm that there are at least 100 different genetic mutations before you could get resistance evolving. In my mind you could spray as much bacculovirus as you like and not worry about resistance.”

Worryingly though, in its most recent tests his team has not been able to adapt the African armyworm virus for use against the fall, though Wilson remains confident that an effective measure will be developed.

A desolate outlook for a bleak future?

Wilson expects that the pest will soon arrive in Yemen and from there could affect southern Europe, northern Europe, and  Asia. He said: “There has been some evidence of a shift polewards of insects and pests”, referring to change in insect behaviour as a result of global warming. He added: “As Europe warms up it could be better for them.”

The fall armyworm has been a pest for generations, but it is now that we are starting to see the potential devastation that could be wrought throughout the world. It could take at least three years before an effective countermeasure can be developed and it will take longer for any new pesticides or bacculovirus strains to be approved for use in the many jurisdictions of the world.