Researchers have identified a naturally occurring soil fungus, Metarhizium rileyi, capable of killing the larval stage of the African armyworm, a pest notorious for devastating key crops such as maize, sorghum, millet, and sugarcane across Africa.

The African armyworm is a migratory caterpillar that not only strips crops of foliage but also damages grazing pastures. This indirectly affects livestock health, as the larvae’s feeding triggers toxic chemical release in grasses like kikuyu, causing poisoning symptoms in cattle.

Challenges of Current Control Methods

Traditional control measures have primarily relied on pyrethroid-based insecticides, which are only effective against very young larvae measuring 1-5 mm. This limitation has resulted in incomplete control and persistent outbreaks, such as the one that affected parts of southern Africa, including South Africa and Zimbabwe, between February and April 2025.

Fungal Biocontrol Discovery

During field inspections in KwaZulu-Natal, South Africa, entomologists observed numerous dead armyworm larvae infected with Metarhizium rileyi. The fungus produces spores that invade and kill the larvae, visible as white and green growths on their bodies.

This marks the first successful isolation and report of this fungus as a natural enemy of the African armyworm in South Africa. Previously, Metarhizium rileyi was recognized for controlling similar pests, such as the fall armyworm in the Philippines.

Implications for Sustainable Pest Management

  • The discovery opens avenues for developing fungal-based biopesticides that offer environmentally friendly pest control options.
  • Mass production and registration of this fungus as a biopesticide could enhance integrated pest management strategies during outbreak seasons.
  • Such biological control agents may reduce reliance on chemical insecticides, minimizing environmental and livestock health risks.

The next steps involve scaling up production and conducting further research to establish commercial viability and regulatory approval for use in affected regions.