Can a newly discovered soil fungus stop the devastating African armyworm when chemicals have failed?

A newly discovered soil fungus, Metarhizium rileyi, has shown promise in controlling the African armyworm, a highly destructive pest that has plagued southern Africa in recent months. The fungus was identified after researchers observed its effects on the larvae of the armyworm during an outbreak in KwaZulu-Natal province in early 2025. The discovery comes amid growing concerns over the diminishing effectiveness of traditional chemical pesticides against the pest. The African armyworm, known for its ability to migrate long distances and devastate crops, has caused widespread damage to maize, sorghum, millet, and sugarcane fields. During the latest outbreak, which spanned from February to April 2025, the pest affected several provinces in South Africa, including KwaZulu-Natal, Limpopo, Gauteng, and Mpumalanga, as well as neighboring Zimbabwe. The larvae, which grow up to 7 cm in length, form dense groups that move across farmland, stripping vegetation down to the ground. Their feeding activity also poses risks to livestock, particularly cattle, due to the release of cyanogenic compounds from the grasses they consume, leading to poisoning symptoms such as abdominal pain, dehydration, and respiratory distress. Traditional methods of controlling the armyworm have relied heavily on synthetic pyrethroid-based insecticides. However, these chemicals are most effective only against young larvae measuring 1–5 mm in length. As the larvae mature, they become increasingly resistant to such treatments, making chemical control less reliable. This limitation has prompted scientists to seek alternative solutions, especially biological ones that target all life stages of the pest. An entomologist specializing in integrated pest management recently published research detailing the discovery of Metarhizium rileyi as a potential biological control agent. The study revealed that the fungus naturally infects and kills the larval instars of the African armyworm. This marks the first documented case of the fungus being isolated and tested in South Africa, despite previous reports of its efficacy against the fall armyworm in countries like the Philippines. During field inspections in KwaZulu-Natal, the researcher observed numerous dead armyworm larvae coated in white and green conidia, aseptical spores produced by the fungus, on both grass blades and the soil surface. These findings suggest that the fungus is actively spreading through the environment and successfully targeting the pest. The presence of the spores on the larvae’s exoskeleton indicates that the infection process is occurring naturally, without human intervention. The discovery of Metarhizium rileyi offers a new avenue for managing the African armyworm, particularly during future outbreaks. Unlike chemical pesticides, which can lose effectiveness over time due to resistance, biological controls like this fungus may provide a sustainable solution. Researchers are now exploring ways to mass-produce the fungus for commercial use as a biopesticide. If registered and approved, it could be deployed alongside existing control measures to enhance overall pest management strategies. Efforts are underway to assess the scalability of using Metarhizium rileyi in agricultural settings. Scientists are evaluating how best to cultivate the fungus in controlled environments and ensure its viability under different climatic conditions. Once these steps are completed, the next phase will involve testing the biopesticide in real-world scenarios to confirm its effectiveness against the armyworm in various ecosystems. The potential application of this fungus extends beyond southern Africa. Given its demonstrated success against similar pests elsewhere, it could be adapted for use in other regions facing similar challenges. Researchers emphasize the importance of continued studies to fully understand the ecological impact of introducing such a biological control agent into new environments. Further investigations are needed to determine the optimal methods for deploying Metarhizium rileyi in large-scale agricultural practices. While initial results are promising, ongoing trials will help establish whether the fungus can consistently suppress armyworm populations without harming non-target organisms. The ultimate goal is to integrate this biological control into existing pest management frameworks, providing farmers with a more resilient tool against this persistent threat.