Fungal Attack on Fall Armyworms: Effects and Process

Jim Crocker
2nd April, 2024

Fungal Attack on Fall Armyworms: Effects and Process

Scanning electron microscopy illustrates the sequential infection cycle of Metarhizium rileyi on Spodoptera frugiperda larvae, progressing from initial conidial attachment and appressoria formation (A–F) through cuticular penetration (G–I) to extensive hyphal colonization and final sporulation (J–O).

Image adapted from: Yang et al. / CC BY (Source)

Key Findings

  • Researchers in China found a fungus, Metarhizium rileyi, can kill fall armyworm pests
  • The fungus infects and overcomes the armyworm's immune defenses, leading to death
  • This biological method could offer an eco-friendly alternative to chemical pesticides
Entomopathogenic fungi are microorganisms that can infect and kill insects, offering a potential eco-friendly alternative to chemical pesticides in managing agricultural pests. One such fungus, Metarhizium rileyi, has garnered attention for its ability to control various caterpillar populations that damage crops like soybeans. Researchers from Shenyang Agricultural University have recently explored the effectiveness of M. rileyi against the fall armyworm, a significant pest that affects crops globally[1]. The fall armyworm, Spodoptera frugiperda, is a moth whose larvae can cause extensive damage to crops, including maize and rice. The economic impact of this pest is substantial, prompting the need for effective control strategies. Chemical insecticides have traditionally been used, but they pose environmental risks and pests can develop resistance to them. Biological control methods, such as using natural predators or pathogens, are being investigated as sustainable alternatives. The study conducted by Shenyang Agricultural University quantified the virulence of M. rileyi strain EFNL-08 against third-instar larvae of the fall armyworm. The research aimed to not only measure how effectively the fungus could kill the larvae but also to understand the infection process and the larva's immune response to the fungal attack. Virulence is a term that describes the degree of damage a pathogen can cause to its host. In this study, researchers observed that M. rileyi effectively infected and killed the fall armyworm larvae. The process begins when the fungus's spores come into contact with the insect's cuticle, the protective outer layer. The spores germinate, and the fungus penetrates the cuticle, eventually reaching the insect's hemolymph, an equivalent to blood in humans. Once inside, the fungus faces the host's immune defenses. Insects have circulating hemocytes, which are cells in their hemolymph that play a role in the immune response, much like white blood cells in mammals. These hemocytes can engulf and destroy foreign particles, a process known as phagocytosis[2]. However, some pathogens, like M. rileyi, have evolved mechanisms to evade or suppress these immune responses. The study at Shenyang Agricultural University detailed how M. rileyi overcomes the armyworm's defenses, leading to the insect's death. This expands upon previous research that documented how another strain of Metarhizium, Metarhizium anisopliae, affects the sand fly vector of Visceral Leishmaniasis by reducing egg hatching and larval survival, and shortening adult lifespan[3]. It also builds on knowledge about insect immune responses to pathogens, as seen in the triatomine bug Rhodnius prolixus, where different hemocyte types react to various threats[2]. The study also ties into earlier findings regarding the dimorphic program of M. rileyi, which is the fungus's ability to change form during infection[4]. This process is regulated by quorum-sensing molecules, which are chemical signals that prompt a coordinated response among fungal cells when they reach a certain density. Understanding this process is crucial as it may reveal targets for enhancing the fungus's effectiveness as a biocontrol agent. The significance of the research extends beyond the laboratory. If M. rileyi can be effectively used in the field, it could reduce the reliance on chemical insecticides, mitigating their environmental impact and the issue of pest resistance. The study provides a foundation for further research into the practical application of M. rileyi and possibly other entomopathogenic fungi in pest management strategies. In conclusion, the work by Shenyang Agricultural University represents an important step in the fight against the fall armyworm. By detailing the virulence of M. rileyi and its interaction with the host's immune system, the study contributes to the understanding of how entomopathogenic fungi can be harnessed in sustainable agriculture. This research underscores the potential of biological control methods in integrated pest management programs, which aim to use a combination of techniques for effective, environmentally sound pest control.

BiochemEcologyMycology

References

Main Study

1) Pathogenicity, infection process, physiological and biochemical effects of Metarhizium rileyi against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) larvae

Published 30th March, 2024

https://doi.org/10.1186/s41938-024-00781-9

Related Studies

2) Phagocytosis of latex beads and bacteria by hemocytes of the triatomine bug Rhodnius prolixus (Hemiptera: Reduvidae).

Journal: Micron (Oxford, England : 1993), Issue: Vol 39, Issue 4, Jun 2008

3) The effects of the fungus Metarhizium anisopliae var. acridum on different stages of Lutzomyia longipalpis (Diptera: Psychodidae).

https://doi.org/10.1016/j.actatropica.2009.10.018

4) Fungal dimorphism in the entomopathogenic fungus Metarhizium rileyi: Detection of an in vivo quorum-sensing system.

https://doi.org/10.1016/j.jip.2016.03.013


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