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RESEARCH ARTICLE (Open Access)

Discovering the ecological roles of entomopathogenic fungi in tropical rainforests

Clement Kiing Fook Wong A B * and Wey Lim Wong B C
+ Author Affiliations
- Author Affiliations

A Department of Agricultural and Food Science, Faculty of Science, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia.

B Centre for Agriculture and Food Research, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia.

C Department of Biological Science, Faculty of Science, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia.




Dr Clement Kiing Fook Wong is a lecturer in Plant Pathology at Universiti Tunku Abdul Rahman, Malaysia. His main area of study is the use of biological control agents in managing pest and disease to facilitate sustainable agriculture.



Dr Wey Lim Wong is a lecturer in Parasitology at Universiti Tunku Abdul Rahman, Malaysia. His research interest includes the study of host-searching behaviour of natural enemies in managing pest population in agriculture.

* Correspondence to: kfwong@utar.edu.my

Microbiology Australia 46(3) 125-129 https://doi.org/10.1071/MA25035
Submitted: 1 July 2025  Accepted: 26 August 2025  Published: 11 September 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the ASM. This is an open access article distributed under the Creative Commons Attribution 4.0 International License (CC BY)

Abstract

Entomopathogenic fungi (EPF) play various ecological roles in maintaining the stability of the tropical rainforests. Besides regulating insect population, EPF contribute significantly to nutrient cycling and tree health. These soil-dwelling fungi interact with arthropods and trees through endophytic and rhizosphere associations. The symbiotic relationship between EPF and plants promotes resistance and tolerance against pests and diseases via host induced systemic and volatile-mediated defence responses. EPF also facilitate nutrient recycling by decomposing insect cadavers and solubilising soil nutrients for plant uptake. Despite their ecological importance, EPF diversity and its ecological function in tropical rainforests remain underexplored. Hence, future research integrating soil nutrient levels, insect populations and tree species is crucial to better elucidate the ecological roles of EPF in tropical rainforests. This review highlights the need for conserving EPF as part of the tropical ecosystems to sustain soil health and forest resilience in the face of deforestation and climate change.

Keywords: biocontrol, conservation, diversity, ecology, entomopathogenic fungi, nutrient cycling, tropical rainforests.

Introduction

Tropical rainforests are complex ecosystems, characterised by elevated temperatures and high rainfall, and are home to a diverse range of microorganisms, plants and animals. The warm and humid conditions facilitate the decomposition of organic matter, forming the nutrient-rich topsoil layer. As a result, microbial communities thrive in fertile forest soils characterised by abundant nutrients, organic matter, moisture and aeration which are crucial for growth and reproduction.1

Entomopathogenic fungi (EPF) are a group of soil fungi that cause infections specifically on insects. They function primarily in the regulating soil-inhabiting insect population. In natural soil conditions, EPF are protected from ultra-violet irradiation from the sun and against biotic and abiotic factors.2 They are also commonly known for their role as biopesticides in the agriculture sector as an environmental-friendly alternative compared to the use of chemicals.2,3 Nonetheless, the ecological services of EPF are far beyond their typical role as pest control in the rainforest. The diversity of EPF is an important indicator of rainforest health. As the population decreases rapidly as a result of deforestation and climate change, there is an urgent need to conserve EPF species.4 They often form intricate interactions with vegetation through nutrient cycling and endophytic relationships, thereby sustaining the stability and health of the rainforest ecosystem4,5 (Fig. 1).

Fig. 1.

The multifaceted ecological roles of EPF in a forest ecosystem.


MA25035_F1.gif

EPF diversity and its general life cycle

To date, there are more than 1000 species of EPF reported to infect insects.6 Most characterised EPF strains are discovered in the orders of Entomophthorales, Onygenales, Neozygitales and Hypocreales.6,7 The Entomophthorales displayed remarkable insecticidal activity but it is technically challenging to grow them on artificial growth media under laboratory conditions.7 As they are biotrophic in nature, this group of host-specific fungi relies on living insects for reproduction and could cause widespread disease outbreaks (epizootics). On the other hand, the generalist Hypocreales are readily cultured on artificial nutrient media due to their saprophytic nature. Hence, they are widely studied for their ecological roles.8 Some notable genera of Hypocrealeans that are widely distributed in tropical rainforests includes Beauveria, Metarhizium, Isaria, Paecilomyces, Purpureocillium, Cordyceps and Ophiocordyceps.916 In nature, certain genera or species of EPF have evolved specific or wide insect host range. For instance, Ophiocordyceps unilateralis alters behaviour of ants by controlling zombified ants to climb to an elevated position before its death to facilitate spore dissemination.13 Various studies in tropical rainforests of China and certain regions of Southeast Asia including Vietnam, Thailand, Indonesia and Malaysia have uncovered diverse and some novel EPF species. Comparative studies generally concluded that lower diversity of EPF was reported in agricultural soils compared to soils from secondary and undisturbed forests thereby highlighting the need for conserving EPF.916

EPF typically live and reproduce in soil for most their life cycle, occurring as asexual spores or conidia in natural, cultivated soils or externally on infected hosts (insect cadavers).5 The population of EPF is influenced by various edaphic factors such as the presence of cover crops, soil texture, pH, levels of organic matter and existing soil microbiota.4,17 Conducive soil environment serves as a reservoir for dormant asexual spores until a susceptible arthropod host is encountered. Alternatively, the soil-dwelling spores may be disseminated to above ground plant parts by wind, rain or insects.18 The life cycle of EPF begins when the spores or conidia come in contact with susceptible host tissue. Upon contact, spore germination is triggered and forms the germ tube. Prior to penetration, the germ tube forms a structure known as appressorium, an important structure that creates a suction pressure onto the insect cuticle, followed by the production of enzymes that degrade insect cuticles, allowing the penetration of hyphae into its insect host. The hyphae continue to colonise its host and finally, produce conidia which will then be dispersed after host death.15 Physically, the infected insects are covered with mycelia and mummified, causing a symptom known as mycosis.5

Ecological roles of EPF

EPF offers essential ecosystem services by suppression of the insect population naturally, promoting tree growth, enhancing tolerance to pests and diseases, while also regulating the soil nutrient cycle in forest soils. Diversity studies of EPF in tropical rainforests are common but information on the ecological roles is scarce.916 Hence, the current review is derived from broader plant and tree species with the aim of providing insights of how EPF can potentially impact the stability of tropical rainforests ecosystem.

A regulator of insect population

The diversity and population of EPF is an indicator of forest health against insect pests’ infestation. Unlike conventional pesticides, EPF do not result in complete elimination of the pest population. They work in a density-dependent manner, suppressing the insect population without causing substantial damage to the overall forest population.8 Unfortunately, there is limited evidence of how EPF regulate the pest population in the natural setting and even less is known on the association of EPF diversity and pest population in forest ecosystems.3,8 Nonetheless, the introduction of specific species of EPF as biological control agents in managing invasive pest species of forest trees including cypress aphids, eucalyptus weevils, Asian long-horned beetles and emerald ash borers have resulted in successful suppression.19 Compared to the immediate effects of pesticides, EPF requires time and suitable climatic conditions to populate and the initial application can be quite costly. As the population establishes itself in the long run, biocontrol might be a better option for sustainable pest management as insect resistance issue is relatively less than pesticide resistance.20

Improving tree health

Aside from being an insect pathogen, EPF are known for their endophytic nature in plants. Endophytes are microbes that thrive in plant tissues without causing any host symptoms while providing several benefits such as plant growth promotion and protection against biotic and abiotic stress.20 In return, the host plants provide carbon and energy, derived from photosynthesis, for the growth and reproduction of EPF.21 The occurrence of endophytic EPF in forest trees has been confirmed by several studies but the tripartite interaction among EPF, forest vegetation, biotic or abiotic stress in the natural state remains unexplored.20,22

In EPF-colonised tissues, the metabolic activity of the host plant changes. Plant volatiles are produced to attract natural enemies of herbivorous insects.20 Other studies have discovered that pests feeding on EPF-colonised plants are more attractive to predators possibly due to weakened immune response and increased attractant (volatile) production by feeding insects.22 Mycosis was also observed in chewing insects that feed on EPF-colonised plants. Hyphae growing within the plant tissue does not produce infectious structure (conidia). As the wounded plant tissues were exposed to the environment during the feeding process, conidiation occurs on the wounded surface hence, providing opportunity for conidia to germinate and penetrate into its host.4,8

EPF-colonised plants often show elevated expression of defence-related genes as part of the host induced systemic defence response (ISR) to prepare plants against future infections.23 During ISR, the heightened production of secondary metabolites, antimicrobials and enzymes are crucial to deter pests and to break down the cell wall of plant pathogens.24 Colonisation of endophytic EPF can occur naturally in plants or by artificial introduction as biopesticides into specific plant organs, increasing host tolerance against pests and diseases.23,24

Soil nutrient cycling

Beyond pathogenicity, EPF play a crucial role in soil nutrient cycling. Although most studies are limited to agriculture crops, these findings could provide useful insights on the possible roles of EPF in regulating soil nutrient in a forest ecosystem. The decomposition of insect cadavers returns nutrient including nitrogen (N) and phosphorus (P) to the soil.25 Solubilisation of soil nutrients such as P and iron (Fe) by EPF were observed in agricultural soils resulting in improved growth and yield of various agricultural crops. These fungi produced organic acids and siderophore, a small Fe-chelating molecule, to enhance the bioavailability of nutrients for plant uptake.26 In addition to nutrient cycling, rhizosphere competent EPF that adhere to the root surface function to protect plant roots from ground-dwelling insects as well as to improve plant growth, possibly through the secretion of plant growth promoting hormones such as indole-acetic-acid (IAA).26,27 Rhizospheric EPF are often attracted to root exudates as their carbon source for growth. Certain genera such as Metarhizium spp. are commonly found to be rhizosphere competent whereas Beauveria spp. are often found in the bulk soil.28 The rhizosphere competence of EPF is also dependent on plant species as colonisation preference could be affected by specific chemical constituents of root exudates.29

Maintaining forest tree diversity

Diverse EPF are associated with greater diversity of forest tree species. EPF protects trees against pest species and ensures balance in soil nutrient cycling. Consequently, a stable population of tree species can be maintained, in which a healthy forest provides nutrient rich soil for EPF to thrive (Fig. 2). Interestingly, EPF were found to exert plant growth promoting properties when soil fertility is optimal. In infertile soil, plant growth is inhibited by EPF. Under nutrient deficient conditions, EPF act as a sink that retrieves nutrients from plants as they compete for resources for survival and reproduction.30 Such observation might also explain the difference of EPF diversity between agricultural and forest soils. Changes in soil edaphic factors such as pH, organic matter and nutrient level significantly affect the population of sensitive EPF species due to competition for space and nutrients.31

Fig. 2.

A proposed interaction between EPF, insect population and tree species in a forest ecosystem.


MA25035_F2.gif

Some studies have demonstrated that EPF diversity in subtropical rainforests and alpine forests of China is affected by not only by soil edaphic factors but also land elevation.31,32 At different elevation, the types of vegetation might have affected the population and pest species leading to changes in EPF diversity. The shift in soil physicochemical properties at various elevation could further influence the number of EPF species present in the bulk soil and rhizosphere.33 Although several EPF census studies were reported in tropical rainforests of Southeast Asia and Southern China, further investigations are required to prove the hypotheses in order to provide a clear understanding on the complex relationship between EPF diversity and tree species in a rainforest ecosystem.916 Important parameters including soil fertility, seasonal changes (i.e. dry and monsoon seasons) and insect population should be taken into consideration when designing such studies.

Conclusion and future perspectives

At present, the ecological roles of EPF in the tropical rainforest ecosystem remain fragmented. Although there are attempts to compare the diversity of EPF species, the outcomes are merely a compilation of species present in different habitats of forest and agricultural lands. Additional studies are therefore necessary to better understand the multifaceted roles of EPF based on the following aspects:

  1. The impacts of elevation, seasonal changes, soil edaphic factors and EPF species on forest tree population and diversity.

  2. The mechanisms of EPF in sustaining tree health through endophytic and rhizospheric interaction.

Conducting such integrative studies might prove to be challenging and time-consuming. Perhaps, it is more manageable to conduct pot trials on saplings of selected forest tree species by artificial inoculation of EPF but parameters such as land elevation can be challenging to simulate. Understanding the complex interaction between EPF and the tropical forest ecosystem is an important step towards conserving EPF, an important indicator of forest health and resilience.

Data availability

Data sharing is not applicable as no new data were generated or analysed during this study.

Conflicts of interest

The authors declare that they have no conflicts of interest.

Declaration of funding

This research did not receive any specific funding.

Acknowledgements

The authors thank the reviewers for providing helpful suggestions and improvement.

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Biographies

MA25035_B1.gif

Dr Clement Kiing Fook Wong is a lecturer in Plant Pathology at Universiti Tunku Abdul Rahman, Malaysia. His main area of study is the use of biological control agents in managing pest and disease to facilitate sustainable agriculture.

MA25035_B2.gif

Dr Wey Lim Wong is a lecturer in Parasitology at Universiti Tunku Abdul Rahman, Malaysia. His research interest includes the study of host-searching behaviour of natural enemies in managing pest population in agriculture.