Insects and Their Beneficial Microbes

Angela E. Douglas

• Publisher: Princeton University Press
• Year: 2022
• Print ISBN: 9780691192406
• eBook ISBN: 9780691236230
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

A comprehensive overview of symbiotic relationships between insects and microbes

Insects and Their Beneficial Microbes is an authoritative and accessible synthesis of insect associations with beneficial microorganisms. Angela Douglas distills the vast literature in entomology and microbiology, as well as the burgeoning microbiome literature, to explore the full scope of insect-microbial interactions and their applications to real-world problems in agriculture and medicine.

Douglas investigates how insects acquire and support their microbial partners, and examines how microorganisms contribute to insect nutrition, the defense against natural enemies, and the detoxification of natural allelochemicals and chemical insecticides. She analyzes how beneficial microbes can be harnessed to solve real-world problems in insect pest management, including strategies to suppress the transmission of viruses and microbial disease agents by mosquitoes and other insects. She also addresses the use of insects as biomedical models for effective microbial therapies treating a range of chronic human diseases, and considers how knowledge of insect-microbial interactions can promote the health of beneficial insects, especially in the context of environmental pollutants and climate change.

Insects and Their Beneficial Microbes provides a much-needed conceptual framework for the growing discipline of insect-microbial interactions, and offers a wealth of insights into insect symbioses from molecular, physiological, ecological, and evolutionary perspectives.

1

Introduction

THE DIVERSITY OF INSECTS AND THEIR MICROBIAL SYMBIONTS

The insects are a supremely successful group of animals, particularly in terrestrial habitats. By the criteria of number of individuals, number of species, ecological importance, and functional diversity, the insects dwarf all other terrestrial animals.

The basis for this book is that associations with beneficial microorganisms make an important contribution to the success of the insects. For example, the role of the leafcutter ants as the dominant herbivores in many Neotropical grassland and forest habitats is founded on their cultivation of plant-degrading fungi in their nests; the obligate blood-feeding lifestyle of bedbugs, sucking lice, and tsetse flies is enabled by internal bacteria that produce vitamins in short supply in vertebrate blood; and many insects, including bumble bees and honey bees, harbor gut microorganisms that protect these insects from virulent pathogens.

In general terms, insect associations with beneficial microorganisms are not exceptional. Most animals host beneficial microorganisms, from which they derive nutrients, protection from natural enemies, or other services (McFall-Ngai et al., 2013). There are, however, two ways in which microbial associations in insects are special. The first is the remarkable diversity of form and function of associations in insects, as discussed in chapters 2–4. The second way relates to the significance of insects to humans. Some insects are pests and disease vectors of agricultural, medical, and veterinary importance, and others are valuable to humans, for example, as pollinators and biological control agents. As our knowledge of insect associations with microorganisms develops, it is becoming increasingly evident that this understanding can be harnessed for novel strategies to control insect pests (chapter 5) and as model systems in biomedical research (chapter 6).

The purpose of this chapter is to provide an overview of the insects and their microbial partners. Section 1.1 introduces the reader to the diversity of insects and microorganisms. Section 1.2 describes the essentials of insect form and function, with an emphasis on the insect structures that provide habitats for microorganisms and insect traits that facilitate and limit microbial colonization. (An extended consideration of insect structure and function is provided by Simpson and Douglas (2013).) In section 1.3, I consider the terminology used to describe interactions involving beneficial microorganisms. Finally, section 1.4 outlines the contents of this book.

1.1 Naming the partners

1.1.1 The insects

There is overwhelming molecular and morphological evidence that the insects are a monophyletic group, comprising some 28 orders grouped within five subclasses (table 1.1 and fig. 1.1A) (Misof et al., 2014). The common ancestor of insects was likely terrestrial, and the earliest fossil insects are from the early Devonian period (ca. 410 million years ago). The class Insecta, together with the classes Collembola (springtails), Protura (coneheads), and Diplura (two-pronged bristletails), comprise the subphylum Hexapoda, which is defined by the possession of three pairs of thoracic legs; insects differ from other hexapods in having external mouthparts. The sister group of the Hexapoda is an obscure group of marine Crustacea, the class Remipedia, with fewer than 30 known species that are apparently restricted to coastal aquifers. In other words, the insects have evolved from within the Crustacea (crabs, lobsters, shrimps, etc.).

Many aspects of the biology of insects are shaped by their body plan, comprising a segmented body with paired jointed appendages (fig. 1.1B), supported by a versatile exoskeleton. This body plan permits rapid and precisely controlled movement, which has facilitated the evolution of complex behavior. It is also well suited to small size, which is associated with high reproductive rates and specialization to a multitude of ecological niches unavailable to larger animals. In addition to these ancestral traits, two evolutionary innovations account for the success of the insects. The first innovation was the origin of flight early in the diversification of the group, with the oldest fossils of winged insects at 324 million years ago in the early Carboniferous era. All extant insects other than the jumping bristletails and silverfish have wings or have evolved from winged insects; a few groups, including the parasitic lice (within the order Psocodea) and fleas (order Siphonaptera), have secondarily lost their wings. The second key innovation was co...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• Preface
• 1. Introduction: The Diversity of Insects and Their Microbial Symbionts
• 2. The Diversity of Insect-Microbial Associations
• 3. How Insects Acquire and Control Their Microbial Symbionts
• 4. Microbial Services
• 5. Harnessing Microbial Symbionts to Manage Insect Pests and Vectors of Disease
• 6. The Insect Microbiome as a Biomedical Model
• 7. Priorities for the Study of Insect-Microbial Associations
• References
• Index