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

Can a newly discovered soil fungus stop the devastating African armyworm when chemicals have failed? Gaby Clark Scientific Editor Andrew Zinin Chief Editor The African armyworm is a highly destructive migratory pest that damages maize, sorghum, millet and sugarcane. These caterpillars also cause indirect damage to livestock by destroying grazing lands and pastures. The last major outbreak of armyworm in southern Africa was from February to April 2025. It affected South Africa's KwaZulu-Natal, Limpopo, Gauteng and Mpumalanga provinces and neighboring Zimbabwe. Controlling armyworm has proved a major challenge. The most common method has been applying a pyrethroid-based synthetic chemical insecticide. But the method has proved less effective in achieving complete control because the insecticide is effective only against larval instars (caterpillars) when they are about 1–5 mm in length and more susceptible to the poison than mature larvae. The insect undergoes complete metamorphosis, consisting of the egg, larva (caterpillar), pupa and adult stages. The adult is a moth. The caterpillar stage is the most damaging. I am an entomologist, and my work focuses mainly on integrated pest management of economically important agricultural insect pests. Specifically, it looks at the use of disease-causing (entomopathogenic) fungi and nematodes as biological control agents of insects in agro-ecosystems. In a recent paper, I set out my findings on a fungus that naturally infects and kills the larval instars of the African armyworm. This is the first report of the presence and successful isolation of the fungus in South Africa. African armyworm killer fungus discovered in South Africa Outbreaks of the African armyworm are mainly characterized by high densities of the insect's larval instars: They form dense armies that move across the ground together. It feeds on plants and can completely strip crop leaves to ground level. Damage to kikuyu grass pastures also means there's less for livestock to eat, and they can get sick from poisoning. This is because when the larvae feed on the grass, it releases a cyanogenic chemical compound as a defense mechanism against the insect. The cyanide compound is toxic to livestock, mostly cattle. Clinical signs of kikuyu grass poisoning in cattle affected during insect outbreaks include abdominal pain, dehydration, excessive drooling of saliva, sham drinking—where affected animals fail to drink even if they put their mouths into the water—incoordination (loss of muscle control, resulting in unsteady and involuntary movements), and cardiac and respiratory distress. When I inspected kikuyu grass pastures infested with the insect in KwaZulu-Natal, I observed that something was killing the larval instars of the African armyworm. It turned out to be an isolate of the fungus Metarhizium rileyi. This fungus lives in soil and is one of many entomopathogens that infect and kill various insect pests. They are often used in agriculture to manage pests that cause severe damage to crops. Several fungus-based insecticides are commercially available and have proven effective. I found that dead African armyworm larvae covered large areas of the fields, mostly attached to blades of grass, with some on the soil surface. They were infected with Metarhizium rileyi. The infection was visible as white and green conidia, which are asexual spores on the insects' cuticle surfaces. This was the first observation and report of the efficacy of this fungus against the African armyworm. Previously, the fungus was reported to be an effective biological control agent of the fall armyworm in countries such as the Philippines. The discovery opens an opportunity to explore and develop this organism as a potential biological control product for use during outbreak seasons in South Africa and other regions globally. Mass production of this fungal species on a commercial scale and registration of the fungus as a biopesticide against the insect would be the next step. It could add to management strategies that can be effectively used during outbreak seasons. Provided by The Conversation This article is republished from The Conversation under a Creative Commons license. Read the original article.