Plant-Herbivore Interactions: Insights from Chemical Ecology and Chemodiversity

Dear Colleagues,

Chemically mediated interactions between plants and herbivores are known as key drivers of ecological and evolutionary processes in terrestrial, marine, and freshwater ecosystems. Herbivores, faced with resources with different nutritional characteristics and palatability, have developed several adaptations that drive plants concomitantly, and consequently, to produce secondary metabolites (SMs), with different patterns of diversification (chemodiversity), forming the basis for chemical ecology. The specific mechanisms through which trophic relations contribute to the diversification of SMs, and ultimately to the maintenance of biodiversity in the environment, as well as their role in structuring biological communities are still to be explored. Despite the knowledge accumulated in decades of study, there are still many gaps that need to be filled, involving, for example, previous and current plant–herbivore interactions at the population level and the observed patterns of conserved SMs (constitutive) versus activated or induced ones.  Further, there is a need to broaden the one-sided focus to different specific life stages at different organizational levels for the entire developmental process and their respective assessments of chemical responses to biological drivers such as herbivory. At the ontogenetic level, there are few analyses of the production of herbivore effectors and the expression of plant defense genes that can considerably expand the range of reproduction targets.

In this Special Issue, original articles, methods, opinions, perspectives, hypotheses, modeling, and reviews exploring these approaches in marine, freshwater, and terrestrial environments will be very welcome. The themes can also be varied, involving aspects such as metabolism, metabolomic, effects of biotic and abiotic factors on chemical mediation, and chemical mediation as a structuring element at different levels of organization.

We are excited to create this Special Issue that covers plant–herbivore chemical interaction in aquatic and terrestrial environments at different scales of chemodiversity in the journal Plants. This Special Edition aims to collect high-quality manuscripts on different aspects involving chemically mediated plant–herbivore interactions.

Prof. Dr. Renato Crespo Pereira
Prof. Dr. Davyson de Lima Moreira
Dr. Bernardo Antonio Perez Da Gama
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• chemical ecology
• chemical mediation
• phenotypic chemical diversity
• plant defense traits
• evolution of chemical defense
• chemodiversity
• chemically mediated interactions
• herbivory

Title: Metabolic networks reveal the innate resistance mechanisms of Wild guava (Psidium cattleianum) against tea mosquito bug, Helopeltis antonii Signoret
Authors: Kamala Jayanthi
Affiliation: Indian Institute of Horticultural Research
Abstract: Wild crop relatives harbour innate host plant defences against insect herbivores compared to the domesticated species. We studied the relative response of the Tea mosquito bug (TMB), Helopeltis antonii Signoret (Hemiptera: Miridae), one of the most damaging insect pests to cultivated Guava (Psidium guajava) along with its wild relatives (Psidium cattleianum, Psidium chinensis, Psidium molle and Psidium friedrichstalianum). Cage assays (no-choice/dual-choice) revealed that P. cattleianum was less preferred over other species. Headspace collection of volatiles from P. guajava and P. cattleianum plants and subsequent olfactometer bioassays (single/dual-choice) further revealed that the volatiles of P. cattleianum significantly repelled the bugs compared to the cultivated species. Electrophysiological studies involving GCEAD/GCMS confirmed the presence of potent repellent chemical cues (β-Ocimene, Tridecane, 1R-α-Pinene, α-Terpinene and Nerolidol) in P. cattleianum which are absent in cultivated species. Post-TMB infestation, the herbivore induced plant volatiles (HIPVs) of P. guajava were found to be more attractive to mirid bugs over P. cattleianum. Upon feeding by H. antonii, cultivated guava leaves developed intense brownish necrotic lesions compared to P. cattleianum. Subsequent biochemical studies revealed a massive secondary metabolites build-up (phenolic acid and flavonoids) as well as increased production of antioxidant enzymes [catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD)] in P. cattleianum over cultivated. The cultivated guava leaves showed decreased POD activity and a build-up of free radicles [Hydrogen peroxide (H2O2)] compared to the wild counterparts which might have led to programmed cell death (localized cell death) resulting in necrotic lesions. LCMS metabolic profiling indicated that the rapid production of specific phenolic acids (t-cinnamic acid, p-coumaric acid, o-coumaric acid, protocatechuic acid, caffeic acid, ferulic acid) and flavonoids (luteolin, catechin, epicatechin, quercetin, myricetin) in P.cattleianum immediately post-infestation and the effective neutralization of H2O2 by antioxidant enzymes might have prevented the programmed cell death. On the contrary, the imbalance generated between H2O2 production and its incomplete removal by antioxidant enzymes/cellular phenolics might have caused significant damage to the leaves of cultivated species, P. guajava, facilitating the development of necrotic lesions, making it more susceptible to TMB infestation. The study offers helpful insights into the innate direct and indirect defences of P. cattleianum and its associated metabolic networks against H. antonii

Title: Olfactory response of the green lacewing Chrysoperla externa to volatile organic compounds and chemical composition of leaf essential oils in Eucalyptus urograndis
Authors: Jean Carlos Santos
Affiliation: Universidade Federal de Sergipe, Departamento de Ecologia, São Cristóvão, SE, Brazil
Abstract: The importance of chemical communication between plants and predators in ecological interactions and integrated pest management cannot be overstated. Studying this communication is essential to understand the intricate relationships between these organisms. This study focused on the behavioral responses of green lacewing Chrysoperla externa (Neuroptera: Chrysopidae) larvae to the volatile organic compounds in young, mature, undamaged, and damaged leaves of saplings of Eucalyptus urograndis (Myrtaceae). In addition, this study investigated the chemical composition of leaf essential oils and their effects on green lacewings. The responses of C. externa larvae to the odors emitted by the leaves were evaluated using an experimental behavioral test with a Y-tube olfactometer. The essential oil was extracted from young and mature leaves, with and without hydrodistillation damage. The larvae exhibited attractive responses to the volatiles emitted without the participation of herbivores and preferentially selected odors emitted by young leaves with simulated herbivory. The chemical composition was analyzed using gas chromatography coupled with mass spectrometry, and 32 compounds were identified, some of which have not been identified in previous studies. This study found that young leaves had a higher essential oil content than mature leaves. Among the identified compounds, eucalyptol, α-Terpineol, Aromadendrene, and α-Terpinyl acetate were the major compounds. An inversion in the content of eucalyptol (which decreased) and α-terpinyl acetate (which increased) was observed when young and mature leaves were damaged. This study provides basic data on the potential use of eucalyptus forests as maintainers of natural chrysopid populations in the field and the development of compounds based on essential oils capable of attracting natural enemies of forest crop pests.