Entomopathogenic and nematophagous fungi serve as sources of fungal formulations that are environmentally friendly for sustainable green control (biological control) of agricultural and forestry pests, and hence are called pest biocontrol fungi. Fungal formulations based on entomopathogenic fungi, such as Beauveria (Cordycipitaceae) and Metarhizium (Clavicipitaceae) in ascomycetous Hypocreales, are named fungal insecticides (acaricides) or mycoinsecticides (mycoacaricides). The environmentally friendly property of such fungal pesticides depends on the nature of fungal cells (conidia or mycelial pellets) formulated as active agents, which infect target pests through cuticular penetration to colonize the host hemocoel for yeast-like budding propagation until host death from mummification but do not cause either pest resistance or environmental residue as usually caused by chemical counterparts. Despite the advantage of such active agents, formulated fungal cells are often sensitive to oxidative stress from host immune response in the infection process, hyperosmotic stress from host hemolymph during hemocoel colonization, and solar ultraviolet (UV) radiation and heat stress in summer. Therefore, aside from easy large-scale production, the fungal biocontrol potential depends not only on fungal pathogenicity and virulence against target pests but also on cellular tolerance / resistance to various stresses encountered in the host and the external environment. Particularly, frequent outbreaksof pest populations occur in summer months characterized by high temperatures and strong solar UV radiation. These conditions are detrimental to formulated fungal cells, thereby negatively affecting the field persistency and efficacy of fungal formulations against arthropod pests. The need to maximize the fungal biocontrol potential has driven the development of fungal stress biology over the past two decades, resulting in great advances both in understanding genetic and molecular principles of fungal resistance to various stresses and in making use of the principles for rational application of fungal pesticides in sunny summer days.
This book comprises eight chapters to summarize the advances in the stress biology of pest biocontrol fungi. Chapters 1-6 provide comprehensive reviews on different topics, followed by Chapters 7 and 8 to present two typical case studies. Chapter 1 focuses on the key roles and principles of mitogen-activated protein kinase (MAPK) signaling pathways that regulate multiple stress responses, which are required for entomopathogenic and nematophagous fungi adapting to the host and the environment. Chapters 2 and 3 turn to pivotal roles of autophagy-related proteins and antioxidant enzymes in orchestrating the fungal biocontrol potential, respectively, followed by molecular insights into entomopathogenic fungal’s tolerance to heat (Chapter 4) and solar UV damage (Chapter 5). Chapter 6 gives an overview of the operation principles of molecular machinery that can recover conidia from solar UV damage to support rational application strategies of fungal insecticides in summer. Chapter 7 presents a basic study that sought to elucidate anti-UV roles and mechanisms of two RAD proteins in the laboratory. Chapter 8 presents a field study to test whether two fungal insecticides applied in the late afternoon to avoid solar UV damage are more efficacious against major rice insect pests than those applied in the morning for exposure to solar UV damage on sunny summer days. A large body of information compiled in this book will benefit researchers in the fields of crop protection and forest protection.
Table of Contents
Chapter 1 MAPK-Cascaded Pathways Required for Adaptation of Entomopathogenic and Nematophagous Fungi to Hosts and Environment 1
1.1 Introduction 2
1.2 Composition of MAPK cascades 4
1.3 Regulatory role of Fus3 cascade 7
1.4 Regulatory role of Hogl cascade 9
1.5 Regulatory role of Slt2 cascade 12
1.6 Functions of three MAPKK-like proteins 14
1.7 Upstream signaling for activation of MAPK cascades 15
1.8 Transcriptional regulation of MAPK cascades 16
1.9 Concluding remarks 18
Acknowledgements 19
References 19
Chapter 2 Autophagy Associated with Fungal Biocontrol Agents’ Adaptation to Host and Environment 27
2.1 Introduction 28
2.2 Autophagy-related proteins in fungal biocontrol agents 29
2.3 Monitoring autophagic events in fungal biocontrol agents 34
2.4 Autophagic events associated with fungal bio-control potential 35
2.5 Regulatory network of autophagy in fungal biocontrol agents 39
2.6 Concluding remarks 39
Acknowledgements 40
References 40
Chapter 3 Antioxidant Enzymes Associated with Biocontrol Potential of Insect Mycopathogens 46
3.1 Introduction 47
3.2 Antioxidant enzymes and their catalytic activities 49
3.3 Contributions of antioxidant enzymes to fungal biocontrol potential 55
3.4 Regulatory network for antioxidant enzymes 58
3.5 Concluding remarks 59
Acknowledgements 60
References 61
Chapter 4 Molecular Basis of Entomopathogenic Fungal Tolerance to Heat Stress 69
4.1 Introduction 70
4.2 Inter-specific and intra-specific variability in fungal heat tolerance 71
4.3 Effects of culture conditions on CHT and related cellular components 74
4.4 Contributions of trehalose and mannitol to fungal heat tolerance 76
4.5 Molecular basis and control of fungal heat tolerance 78
4.6 Genetic improvement of fungal heat tolerance 84
4.7 Safety of heat-tolerant fungal insecticides to apiculture 86
4.8 Concluding remarks 87
Acknowledgements 88
References 89
Chapter 5 Molecular Basis of Entomopathogenic Fungal Resistance to Solar UV Radiation 101
Chapter 6 Molecular Machinery Supporting Recovery of Conidia from Solar UV Damage and Rational Application of Mycoinsecticides 137
Chapter 7 Radi and Radio Tied to Photolyase Regulators Acquire High Photoreactivation Activity to Protect Insecticidal Fungal Cells from Solar UV Damage 163
Chapter 8 Fungal Insecticides Applied in Late Afternoon Are More Efficacious against Rice Insect Pests than Those Applied for Exposure to Solar UV Damage in the Morning 201
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Research and Application Advances in Stress Biology of Pest Biocontrol Fungi
