Co‐option of microbial associates by insects and their impact on plant–folivore interactions

Abstract

Plants possess a suite of traits that make them challenging to consume by insect herbivores. Plant tissues are recalcitrant, have low levels of protein, and may be well defended by chemicals. Insects use diverse strategies for overcoming these barriers, including co-opting metabolic activities from microbial associates. In this review, we discuss the co-option of bacteria and fungi in the herbivore gut. We particularly focus upon chewing, folivorous insects (Coleoptera and Lepidoptera) and discuss the impacts of microbial co-option on herbivore performance and plant responses. We suggest that there are two components to microbial co-option: fixed and plastic relationships. Fixed relationships are involved in integral dietary functions and can be performed by microbial enzymes co-opted into the genome or by stably transferred associates. In contrast, the majority of gut symbionts appear to be looser and perform more facultative, context-dependent functions. This more plastic, variable co-option of bacteria likely produces a greater number of insect phenotypes, which interact differently with plant hosts. By altering plant detection of herbivory or mediating insect interactions with plant defensive compounds, microbes can effectively improve herbivore performance in real time within and between generations.

Stress priming, memory, and signalling in plants

“…Particular emphasis is placed on the role of chromatin organization, transcription factors, posttranslational modifications, phytohormones, and metabolites involved in stress management. Plant responses do depend not only on the plant's intrinsic capability to cope with a specific stress but also on habitat conditions and the availability of symbionts, as pointed out by Douma et al () and Mason, Jones, and Felton () in this issue.…”

“…These bacteria induce the SA pathway, which suppresses the wound‐induced JA‐regulated defence, thus attenuating the plant‐defensive effects on the larvae (Chung et al, ). Mason et al () review current knowledge on the role of microbes in plant–insect interactions and emphasize that studies on plant defences against herbivory should not only consider the two counterparts, that is, the plants and herbivores, but also take into account the hidden players, that is, symbiotic microbes associated with the herbivores and plants.…”

Microbiome of the larvae of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) from maize plants

“…The common associations between insect guts and bacteria are facultative in nature and seem to perform context-reliant functions (Manson, Jones, & Felton, 2018). Caterpillars (larvae) of Lepidoptera have been suggested to naturally lack resident gut symbionts (Hammer, Janzen, Hallwachs, Jaffe, & Fierer, 2017).…”

Bacterial communities of herbivores and pollinators that have co-evolved Cucurbita spp

“…Many microbes ingested by insects likely pass transiently through the digestive tract and may not confer any impact on the host insect (Oliver et al 2008, Hammer et al 2017, Hammer et al 2019). However, some microbes are able to colonize insects as hosts, and can have diverse and consequential – yet often cryptic – roles in mediating ecological interactions between plants, other insects and other microbes (Shapiro et al 2012, Chung et al 2013, Shapiro et al 2013, Wang et al 2016, Mason et al2018). For example, many pollinators likely transfer microbes between flowers during normal foraging that may directly affect other visiting insects, or indirectly alter traits determining floral attractiveness (Yang et al, McArt et al 2014, Ravoet et al 2014, Vannette and Fukami 2016, Rering et al 2018, Figueroa et al 2019).…”