Molecular Rationale of Insect-Microbes Symbiosis—From Insect Behaviour to Mechanism

Abstract

Insects nurture a panoply of microbial populations that are often obligatory and exist mutually with their hosts. Symbionts not only impact their host fitness but also shape the trajectory of their phenotype. This co-constructed niche successfully evolved long in the past to mark advanced ecological specialization. The resident microbes regulate insect nutrition by controlling their host plant specialization and immunity. It enhances the host fitness and performance by detoxifying toxins secreted by the predators and abstains them. The profound effect of a microbial population on insect physiology and behaviour is exploited to understand the host–microbial system in diverse taxa. Emergent research of insect-associated microbes has revealed their potential to modulate insect brain functions and, ultimately, control their behaviours, including social interactions. The revelation of the gut microbiota–brain axis has now unravelled insects as a cost-effective potential model to study neurodegenerative disorders and behavioural dysfunctions in humans. This article reviewed our knowledge about the insect–microbial system, an exquisite network of interactions operating between insects and microbes, its mechanistic insight that holds intricate multi-organismal systems in harmony, and its future perspectives. The demystification of molecular networks governing insect–microbial symbiosis will reveal the perplexing behaviours of insects that could be utilized in managing insect pests.

The role of Drosophila microbiota in gut homeostasis and immunity

“… 5 , 6 Microbiomes contribute to nearly every aspect of animal biology including pathogen susceptibility and autoimmunity, adaptation to environmental stresses, range expansion, and metabolism. 7 For instance, molecular advances show that numerous marine invertebrates require transient microbe-derived chemical cues, often associated with biofilms, to proceed from one developmental stage to the next. 8–10 Additionally, bacteria that shelter in the human gut and intestines assist in digesting endogenous and exogenous carbohydrates, provide vitamins, and maintain immune homeostasis.…”

Insect-Microorganism Interaction Has Implicates on Insect Olfactory Systems

“…Some microorganisms do not have active dispersal mechanisms of their own and need to use external forces, such as insect vectors, to help them spread [21][22][23]. In addition, a variety of microorganisms are nourished by insects, which coexist alongside their hosts [24], and many microorganisms also have remarkable influences on insect biological processes such as development [25], physiology [26], nutrition [27], survival [28], immunity [29], and even vector competence [30]. Thus, throughout the long period of co-evolution, insects have formed close relationships with microorganisms, which interact with and depend on each other, and evolve in concert [31][32][33][34].…”

Pathophysiology and transcriptomic analysis of Picea koraiensis inoculated by bark beetle-vectored fungus Ophiostoma bicolor

“…Both beetle and fungal partners have developed from occasional and sporadic to relatively stable and intimate relationship during their historical co-occurrence in the same habits ( Bleiker and Six, 2009 ; Biedermann and Vega, 2020 ; Chakraborty and Roy, 2021 ; Singh et al, 2021 ). The benefits of beetle vectors to fungi are evident; for example, beetles can bring the fungi to new hosts and create inoculation holes.…”