A naturally occurring soil fungus has been identified as a potential biological control agent against the African armyworm, one of the most destructive crop pests in eastern and southern Africa, according to new research by South African entomologist Letodi Luki Mathulwe.
The discovery began when Mathulwe, working for the agriculture department in KwaZulu-Natal, investigated fields of dead caterpillars covered in a white substance. The substance turned out to be a fungus that was killing the armyworms, whose name comes from their march-like advance through crops.
Discovery in Kikuyu grass fields
In 2025, an outbreak of African armyworm (Spodoptera exempta) started in northern South Africa and by April had reached KwaZulu-Natal. Mathulwe received daily panicked calls from farmers finding caterpillars in their fields. She went to the countryside and found the dead insects in Kikuyu grass, which is crucial for livestock grazing.
“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.
Mathulwe, who had studied fungi for pest control, collected samples of dead armyworms and the fungus, and tested them at her laboratory in Pietermaritzburg. Her team's results, published in a peer-reviewed paper, confirmed the fungus could be used against the armyworms.
Breakthrough against mature populations
This is a major breakthrough, Mathulwe said, because while chemical treatments exist for early-stage caterpillars, nothing has been effective against mature populations. The African armyworm eats staple crops like maize and sorghum, and releases a chemical compound in grass that can make cattle sick.
The impact is severe. A 2017 outbreak destroyed up to 40% of Zambia's maize production. It also drives up food prices and strains government budgets. Last year's outbreak caused problems in Zimbabwe, where inflation hit 736% in 2024, and Malawi, where it reached 35% in 2024.
Developing a natural product
The armyworm causes most damage as a caterpillar but is also hard to control as a moth, enabling migration. “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 noted that more testing is needed before a product is ready for 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.
