Diversity of entomopathogenic fungi (EPF) in soil across adjacent forest and pasture habitats and their interactions with arthropod hosts : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand

Abstract

Entomopathogenic fungi (EPF) are natural pathogens of insects that play a critical role in regulating arthropod populations and maintaining ecological balance. These fungi are commonly found in the soil, where they interact with invertebrates and with other microorganisms, making soil an essential reservoir for collecting EPF isolates. Understanding the distribution and prevalence of EPF across different habitats is crucial for their effective utilization in the biological control of agricultural pests. In this thesis, the diversity of entomopathogenic fungi (EPF) in adjacent forest and pasture habitats of the North Island, New Zealand, was comprehensively investigated. This study utilized an integrative approach, combining traditional techniques such as insect baiting and semi-selective plating with advanced molecular methods, including metagenomics and metabarcoding, to explore EPF communities across these contrasting habitats. In Chapter 1, I introduced the current understanding of EPF and identified key research gaps, setting the foundation for the study. Chapter 2 focused on the incidence of EPF across forest, forest-pasture boundary, and pasture habitats and the association with soil invertebrates. The results showed the highest EPF prevalence in forest soils, followed by boundary zones and finally pastures, demonstrating the influence of habitat conditions on EPF diversity. In Chapter 3, I characterized EPF isolates, primarily Beauveria spp. and Metarhizium spp., and found that forest and boundary soils caused up to 80% mortality in Tenebrio molitor larvae within seven days, indicating their insecticidal potential. Chapter 4 expanded the analysis by applying metagenomic and metabarcoding approaches, revealing additional fungal taxa, such as Cordyceps, Lecanicillium and Ophiocordyceps, which traditional methods could not detect. Chapter 5 assessed the efficacy of EPF isolates against agricultural pests, with pasture-derived isolates achieving higher pathogenicity and potential as cost-effective biocontrol agents. Finally, in Chapter 6, I synthesized these findings, emphasizing the ecological importance of soil habitats as reservoirs for EPF diversity and the adaptability of local isolates to specific environments. I recommended future research to expand studies into transitional zones, conduct field trials, and investigate the evolutionary mechanisms underpinning EPF adaptation and pathogenicity.