Fungus offers alternative for biological control of fall armyworm

Published research analyzed the immune responses of Spodoptera frugiperda to the entomopathogenic fungus Metarhizium rileyi, a promising alternative for the biological control of this insect.

The study, conducted by researchers at the China Institute of Agricultural Sciences, used RNA sequencing and microscopic observation to understand how third-instar larvae of the S. frugiperda react to fungal infection at different stages.

The results indicate that the caterpillar's immune response changes as the infection progresses, providing key insights for improving the efficacy of biopesticides.

The research identified three main stages of fungal infection in the fall armyworm:

• Fungal penetration into the cuticle (0-48h): In this initial phase, M. rileyi releases enzymes to break through the insect's external barrier. In response, the caterpillar activates metabolic pathways related to energy, detoxification, and melanization. Immunological actions such as the Toll and IMD signaling pathways are activated to fight the infection.

• Internal fungal infection (48-96h): During this period, the fungus spreads through the hemolymph and reaches peak expression of genes related to the insect's immune system. The cellular response becomes predominant, with hemocytes encapsulating and phagocytosing hyphal bodies. Phagocytosis intensifies due to increased expression of genes associated with the production of reactive oxygen species (ROS) and hormone biosynthesis.

• Fungal emergence and host death (96-120h): In this final phase, immune activity is paralyzed and the caterpillar dies. The fungus emerges from the insect's cuticle, forming new conidia to infest other individuals.

The study findings reinforce the potential of M. rileyi as biocontrol of S. frugiperda. However, some limitations still need to be overcome, such as the prolonged time of action and the need to improve the virulence of the fungus for different stages of the caterpillar life cycle. The results provide support for the engineering of more effective strains and the development of next-generation biopesticides.

Extras:

• The article can be read at doi.org/10.3390/insects16020199

• Cultivar Magazine published an article on the "bioinsecticidal potential of the fungus Metarhizium rileyi" in 2020

• Learn more about "Spodoptera frugiperda"