Halting the march of the armyworm: fungus discovery offers hope to African farmers

Hearing about fields full of dead caterpillars enveloped in a mysterious white substance intrigued the South African scientist Letodi Luki Mathulwe. Something was killing off the African armyworm – one of the most devastating pests for farmers in east and southern Africa.The white substance was a naturally occurring fungus and it was wiping out the caterpillar, which gained its name from its march-like advance through fields of crops.An outbreak of African armyworm (Spodoptera exempta) in 2025 had started in northern South Africa and by April had reached the eastern province of KwaZulu-Natal, where Mathulwe was working for the agriculture department. Every day she was getting panicked calls from local farmers who were finding the caterpillars in their fields.Mathulwe went out to the KwaZulu-Natal countryside to see for herself and it was there, in the fields of Kikuyu grass – crucial grazing for livestock – that she realised she had made an important discovery.Armyworms eating grass. A soil fungus could offer a new way to tackle the hugely destructive caterpillars where chemical controls have fallen short. Photograph: Letodi Luki Mathulwe“Something was killing the insects naturally. I was intrigued because in other areas the insects were alive and destroying the grass but as soon as they come here, there’s something that is killing them,” she said.As an entomologist who had studied the use of fungi to kill insect pests, Mathulwe immediately gathered samples of the dead armyworms and the fungus to test at her laboratory in Pietermaritzburg.Her team’s results, now presented in a peer-reviewed research paper, showed she was right in her hunch that the fungus could be used in the fight against the armyworms.It was a major breakthrough, said Mathulwe, because while there are chemical treatments for dealing with the caterpillars in the early stages of life, nothing has proven effective against mature populations.The African armyworm not only eats staple crops such as maize and sorghum but also releases a chemical compound in grass that can make cattle sick.The impact can be brutal for farmers. One outbreak in 2017 was estimated to have destroyed up to 40% of Zambia’s maize production.Major outbreaks of armyworms have threatened the food security of some African countries. Photograph: Courtesy of Letodi Luki MathulweIt also sends food prices soaring and puts strain on government budgets. Last year’s outbreak caused problems for farmers in countries such as Zimbabwe, where inflation had hit 736% in 2024, and Malawi, where it reached 35% in 2024.The African armyworm causes the most damage in its caterpillar stage but is also hard to control when it develops into a moth, allowing populations to migrate.“When we discovered this fungus, we realised we could develop this into a product that can be eventually used when the next outbreak happens,” said Mathulwe.“I think it will be a great thing – it will eventually eliminate the fear for farmers that the insect creates because once it’s present within grazing fields, farmers start to panic.”Mathulwe said there was still more work and more testing to do in developing a product for use by farmers.“I think it will create a lot of hope for farmers, because it will mean that their animals won’t get sick if the farmer is able to control the presence of the insects within their field,” she said.