Plant resistance towards insect herbivores: a dynamic interaction

Rice master regulator 'HYR' enhances growth and defense mechanisms with consequences for fall armyworm growth and host selection

Rice (Oryza sativa L.), the staple food for half of the world's population, suffers heavy damage by insect herbivores, especially the emerging fall armyworm (FAW), Spodoptera frugiperda. HIGHER YIELD RICE (HYR), a master regulator of multiple biological pathways with an established gene regulatory network, has been found to improve rice yield to ∼29% and tolerance to environmental stress. However, its impact on defense has not been explored. We hypothesized that, FAW would target HYR plants because of its vigorous growth and lead to trade-offs for defense. Through a series of experiments with HYR and its wild type (WT), we show that HYR plants have enhanced below-ground growth, physiological traits, and direct and indirect defense traits including leaf trichomes, wax, and volatile organic compounds. To test possible phytohormone-mediated defense signaling, we focussed on jasmonic acid and salicylic acid gene expression panel and found that most of these genes are highly expressed in HYR when compared to its WT counterpart. Bioassays examining developmental milestones also revealed that HYR plants effectively deter FAW, and when force-fed, caused negative effects. Collectively, our findings suggest that the master regulator HYR (Higher Yield Rice expressing) plants enhance growth and physiological traits, as well as physical and chemical defense mechanisms through co-ordinated defense gene expression, which deter herbivore feeding, growth, development, and host selection.

The plant-beneficial fungus Trichoderma harzianum T22 modulates plant metabolism and negatively affects Nezara viridula

BACKGROUND

Plant-beneficial fungi play an important role in enhancing plant health and resistance against biotic and abiotic stresses. Although extensive research has focused on their role in eliciting plant defences against pathogens, their contribution to induced resistance against herbivorous insects and the underlying mechanisms remain poorly understood. In this study, we used insect bioassays and untargeted metabolomics to investigate the impact of root inoculation of sweet pepper with the plant-beneficial fungus Trichoderma harzianum T22 on direct defence responses against the insect herbivore Nezara viridula.

RESULTS

We observed reduced relative growth rate of N. viridula on leaves of fungus-inoculated plants, with no change in mortality. Untargeted metabolomic analyses revealed that inoculation with T. harzianum did not affect the leaf metabolome in the absence of herbivory five weeks after inoculation. However, compared to non-inoculated plants, inoculated plants exhibited significant metabolic alterations in herbivore-damaged leaves following N. viridula feeding, while changes in the metabolic profile of distant leaves were less pronounced. Notably, metabolites involved in the shikimate-phenylpropanoid pathway, known to be involved in plant defence responses, displayed higher accumulation in damaged leaves of inoculated plants compared to non-inoculated plants.

CONCLUSION

Our results indicate that root inoculation with T. harzianum T22 affects plant defences against N. viridula, leading to reduced insect performance. Metabolite-level effects were primarily observed in damaged leaves, suggesting that the priming effect mainly results in localized metabolite accumulation at the site of attack. Future research should focus on identifying the detected compounds and determining their role in impairing N. viridula performance.

Auxin-salicylic acid seesaw regulates the age-dependent balance between plant growth and herbivore defense

According to the plant vigor hypothesis, younger, more vigorous plants tend to be more susceptible to herbivores compared to older, mature plants, yet the molecular mechanisms underlying this dynamic remain elusive. Here, we uncover a hormonal cross-talk framework that orchestrates the age-related balance between plant growth and herbivore defense. We demonstrate that the accumulation of salicylic acid (SA), synthesized by Nicotiana benthamiana phenylalanine ammonia-lyase 6 (NbPAL6), dictates insect resistance in adult plants. NbPAL6 expression is driven by the key transcription factor, NbMYB42, which is regulated by two interacting auxin response factors, NbARF18La/b. In juvenile plants, higher auxin levels activate NbmiR160c, a microRNA that simultaneously silences NbARF18La/b, subsequently reducing NbMYB42 expression, lowering SA accumulation, and thus weakening herbivore defense. Excessive SA in juvenile plants enhances defense but antagonizes auxin signaling, impairing early growth. Our findings suggest a seesaw-like model that balances growth and defense depending on the plant's developmental stage.

The Role of Phenylpropanoids and the Plant Microbiome in Defences of Ash Trees Against Invasive Emerald Ash Borer

Plants have coevolved with herbivorous insects for millions of years, resulting in variation in resistance both within and between species. Using a manipulative experiment combined with untargeted metabolomics, microbiome sequencing and transcriptomics approaches, we investigated the roles of plant metabolites and the microbiome in defence mechanisms in native resistant Manchurian ash (Fraxinus mandshurica) trees and non-native susceptible velvet ash (Fraxinus velutina) trees against the highly invasive emerald ash borer (EAB, Agrilus planipennis). Comparative transcriptomics and metabolomics analyses show that the phenylpropanoid pathway, which is enriched in differentially expressed genes and differentially abundant metabolites, may serve as a potential regulator of resistance. Additionally, the microbiome is distinctly shifted in two ash species. Indicator taxa analysis reveals that the distinct genera are dominant in the galleries of two ash species, for example, Pseudomonas in velvet, and Hafnia-Obesumbacterium in Manchurian. The strong correlation between indicator taxa and metabolites suggests that the chemical compounds might impact the microbial community in phloem directly or indirectly, or vice versa. This study significantly enhances our understanding of the variation in resistance between ash species and its contribution to the invasion success of EAB, providing valuable insights for the development of pest management strategies.

High Nitrogen Enhances Maize Susceptibility to Holotrichia parallela via β-Caryophyllene-Mediated Olfactory Recognition and Jasmonate Suppression

Excessive nitrogen application not only affects plant development but also significantly influences plant-pest interactions. This study investigates how nitrogen fertilization modifies the metabolism of maize (Zea mays) and its interaction with Holotrichia parallela, a key soil-dwelling pest. High-nitrogen (HN) conditions increased the emission of volatile organic compounds (VOCs), with β-caryophyllene and palmitic acid strongly attracting larvae behavior selection, and β-caryophyllene attracting female oviposition. RNA interference targeting HparOR19 and HparOR22 genes confirmed the role of β-caryophyllene in pest olfactory recognition. Conversely, low-nitrogen (LN) conditions stimulated jasmonic acid (JA)-related defenses, while HN promoted the production of primary metabolites such as glucose, fructose, and sucrose, which act as feeding stimulants. These findings highlight the intricate relationship among nitrogen fertilization, maize metabolism, and pest behavior, underscoring the necessity of integrating metabolic insights into effective pest management strategies.

From Digestion to Detoxification: Exploring Plant Metabolite Impacts on Insect Enzyme Systems for Enhanced Pest Control

This review provides an in-depth examination of the intricate interactions between plant metabolites and the digestive and antioxidative enzymes in insects, highlighting their essential roles in shaping insect herbivory and adaptation strategies. Plants have evolved a diverse arsenal of secondary metabolites to defend against herbivorous insects, which, in response, have developed sophisticated adaptations to overcome these defenses and efficiently exploit plant resources. We outline the importance of digestive enzymes, such as proteases and amylases, which allow insects to break down complex plant compounds and access vital nutrients. Additionally, the review focuses on antioxidative enzymes in the insect midgut, including superoxide dismutase and catalase, which play a crucial role in mitigating oxidative stress generated during digestion and other metabolic processes. Synthesizing findings from various studies, this review also considers how environmental factors, such as heavy metal exposure and temperature changes, influence these enzymes' activity levels. It highlights the dual function of antioxidative enzymes in detoxifying harmful plant-derived compounds while preserving cellular stability. The implications of these biochemical interactions for pest management are discussed, with an emphasis on the potential for developing biopesticides that target specific enzymatic pathways to disrupt insect feeding and growth. By elucidating the biochemical mechanisms that underlie plant-insect interactions, this review enhances our understanding of co-evolutionary dynamics and offers insights into sustainable agricultural practices that could leverage these interactions for effective pest control. Finally, the review proposes future research directions aimed at identifying novel plant metabolites with enzyme-modulating properties and exploring the ecological impacts of enzyme-targeted pest management approaches.

Pepper feeding derivative Brucella sp. in the gut of Spodoptera litura (Lepidoptera: Noctuidae) affect the growth and development of host larvae

BLTY is a pepper cultivar that has resistance to young larvae of Spodoptera litura Fabricius, whereas FXBX is a pepper cultivar suitable for the growth of S. litura larvae. The obtained microbiomics data suggest that the BLTY leaves fed S. litura larval guts inhabited more Brucella. In this study, two Brucella spp. (2FC-4 and 2FC-15) and one Microbacterium sp. (2FC-22) were isolated from the guts of BLTY and FXBX leaf-fed S. litura, respectively. The loading of 2FC-4 and 2FC-15 reduced the survival rate, average larval weight, diet consumption, pupation rate, and emergence rate of S. litura, whereas the efficacy of 2FC-22 was in contrast with that of the two Brucella spp. By constructing the germ-free (GF) and 2FC-4, 2FC-15, or 2FC-22 mono-associated gnotobiotic S. litura larvae, we found that the loading of 2FC-4 and 2FC-15 disrupted the peritrophic membrane and midgut walls of the tested larvae. In addition, the loading of 2FC-4 or 2FC-15 increased the juvenile hormone content and decreased the ecdysone content in S. litura. The loading of 2FC-4 or 2FC-15 decreased the activities of protease, trehalose, amylase, and invertase and increased the activities of SOD, CAT, and POD. In this study, we analyzed the resistance of BLTY to S. litura from the perspective of the gut microbiota; the selected Brucella sp. can be used for the biological control of Spodoptera pests and Microbacterium sp. can be used as an additive in the daily maintenance of Spodoptera populations.

Comparative Transcriptome Analysis Reveals Expression of Defense Pathways and Specific Protease Inhibitor Genes in Solanum lycopersicum in Response to Feeding by Tuta absoluta

Understanding plant-insect interactions can help control the harm of herbivorous pests. According to transcriptome data, transcripts of Solanum lycopersicum responding to feeding by Tuta absoluta were screened for important endopeptidase inhibitors. These genes were annotated as serine-type endopeptidase inhibitors from the potato inhibitor I family, potato type II proteinase inhibitor family, and soybean trypsin inhibitor (Kunitz) family. Based on the analysis of expression patterns, Solyc09g084480.2, Solyc03g020080.2, Solyc03g098760.1, and Solyc01g009020.1 were identified as key genes in the defense system of S. lycopersicum. The major endopeptidase genes such as Tabs008250, Tabs007396, and Tabs005701 in the larval stages of T. absoluta were also detected as potential targets of the plant endopeptidase inhibitors. The interaction mode between these endopeptidase and endopeptidase inhibitors was predicted based on the protein structure construction. This study aims to reveal the molecular response of S. lycopersicum to feeding by T. absoluta with high throughput sequencing and bioinformatics analysis.

Comparative translational reprogramming of Glycine max during mechanical wounding

Glycine max (soybean) is a highly protein-rich legume that also contains oils and vitamins. Unfortunately, soybean faces many biotic and abiotic stresses including heat, drought, pests, wounds, infections, and salinity, which limits the crop productivity. Among these, mechanical wounding (MW) causes significant harm to plants, creates a passage for invading pathogens, and disrupts plant metabolism. Thus, exploring soybean responses at the molecular and biochemical levels during mechanical damage is essential. Additionally, MW resembles insect bites, which offers important insights into the immune systems identical to MW and pest attacks. In this investigation, we executed a comparative proteome evaluation of the PUSA9712 soybean variety following MW. Based on specifications of log2FC ≥ 1 and p-value ≤ 0.05, the study disclosed 786 differentially abundant proteins (DAPs) upon MW, among which 294 were elevated and 492 were down-regulated. The function annotation and pathway analysis of DAPs displayed their role in ROS signaling, flavonoid biosynthesis, ABA synthesis, JA-synthesis, defense against pathogens, fatty acid synthesis, brassinosteroid (BR) signaling, carbohydrate metabolism, proteolysis, calcium signaling, and protein kinase pathway. Lipoxygenase, V-type ATPases, Annexin, NsLTP, and ATP-dependent Clp protease proteolytic subunit DAPs can be promising candidates to strengthen soybean crop's resilience to mechanical damage and pest/pathogen attacks and need further functional characterisation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-025-01562-w.

Compounds Involved in the Invasive Characteristics of Lantana camara

Lantana camara L. is native to tropical America and has naturalized in many other tropical, subtropical, and temperate regions in Asia, Africa, Oceania, North and South America, and Europe. L. camara infests diverse habitats with a wide range of climatic factors, and its population increases aggressively as one of the world's 100 worst invasive alien species. Its infestation reduces species diversity and abundance in the natural ecosystems and reduces agricultural production. The life history characteristics of L. camara, such as its high reproductive ability and high adaptive ability to various environmental conditions, may contribute to its ability to infest and increase its population. Possible evidence of the compounds involved in the defense functions of L. camara against natural enemies, such as herbivore mammals and insects, parasitic nematodes, pathogenic fungi and bacteria, and the allelochemicals involved in its allelopathy against neighboring competitive plant species, have accumulated in the literature over three decades. Lantadenes A and B, oleanonic acid, and icterogenin are highly toxic to herbivore mammals, and β-humulene, isoledene, α-copaene thymol, and hexadecanoic acid have high insecticidal activity. β-Caryophyllene and cis-3-hexen-1-ol may function as herbivore-induced plant volatiles which are involved in sending warning signals to undamaged tissues and the next plants of the same species. Farnesol and farnesal may interrupt insect juvenile hormone biosynthesis and cause abnormal metamorphosis of insects. Several triterpenes, such as lantanolic acid, lantoic acid, pomolic acid, camarin, lantacin, camarinin, ursolic acid, and oleanonic acid, have demonstrated nematocidal activity. Lantadene A, β-caryophyllene, germacrene-D, β-curcumene, eicosapentaenoic acid, and loliolide may possess antimicrobial activity. Allelochemicals, such as caffeic acid, ferulic acid, salicylic acid, α-resorcylic acid, p-hydroxybenzoic acid, vanillic acid, unbelliferone, and quercetin, including lantadenes A and B and β-caryophyllene, suppress the germination and growth of neighboring plant species. These compounds may be involved in the defense functions and allelopathy and may contribute to L. camara's ability to infest and to expand its population as an invasive plant species in new habitats. This is the first review to focus on how compounds enhance the invasive characteristics of L. camara.

Protein Dynamics in Plant Immunity: Insights into Plant-Pest Interactions

All living organisms regulate biological activities by proteins. When plants encounter pest invasions, the delicate balance between protein synthesis and degradation becomes even more pivotal for mounting an effective defense response. In this review, we summarize the mechanisms by which plants regulate their proteins to effectively coordinate immune responses during plant-pest interactions. Additionally, we discuss the main pathway proteins through which pest effectors manipulate host protein homeostasis in plants to facilitate their infestation. Understanding these processes at the molecular level not only deepens our knowledge of plant immunity but also holds the potential to inform strategies for developing pest-resistant crops, contributing to sustainable and resilient agriculture.

HcCYP6AE178 plays a crucial role in facilitating Hyphantria cunea's adaptation to a diverse range of host plants

Strong multi-host adaptability significantly contributes to the rapid dissemination of Hyphantria cunea. The present study explores the involvement of cytochrome P450 monooxygenase (P450) in the multi-host adaptation of H. cunea and aims to develop RNA pesticides targeting essential P450 genes to disrupt this adaptability. The results showed that inhibiting P450 activity notably reduced larval weight and food-intake across seven plants groups. The P450 gene HcCYP6AE178 was highly upregulated in H. cunea larvae from medium- and low-preference host plant groups. Silencing HcCYP6AE178 significantly decreased H. cunea larval body weight, increased larval mortality, inhibited energy metabolism genes expression and interfered with growth regulatory genes expression. Overexpression of HcCYP6AE178 enhanced the tolerance of Drosophila and Sf9 cells to the plant defensive substances cytisine and coumarin. The RNA pesticide CS-dsHcCYP6AE178 constructed using chitosan (CS) exhibited remarkable stability. Treatment with CS-dsHcCYP6AE178 effectively reduced H. cunea larval body weight, heightened larval mortality, and disrupted growth regulatory genes expression in low-preference host plant groups. Combined treatment of CS-dsHcCYP6AE178 and coumarin significantly elevated H. cunea larval mortality compared to coumarin alone, accompanied by the inhibition of growth regulatory genes expression and an abnormal increase in energy metabolism genes expression. Taken together, HcCYP6AE178 is essential for the adaptation of H. cunea to multiple host plants, and RNA pesticides targeting HcCYP6AE178 can effectively impair the performance of H. cunea in different host plants.

Effects of Larch Woolly Adelgid Infestation on Morphological, Histological and Allelochemical Traits of European Larch Needles

The study was carried out to assess the effect of the larch wooly adelgid Adelges laricis Vallot (Hemiptera: Adelgidae) infestation on its secondary host, the European larch Larix decidua Mill. Morphology and anatomy of adelgid-infested needles, and content of defense phenolic compounds including individual flavonoids isorhamnetin, kaempferol, quercetin, rutin, catechin, epicatechin, apigenin, ampelopsin and taxifolin, were analyzed. The amount of total phenols in needles from adelgid-infested twigs of L. decidua increased following the development of the A. laricis population, from the end of April until the end of June. The most abundant among flavonoids were the flavanols, mainly catechin and epicatechin, which predominated in the larch needles during the whole period of adelgid infestation. The content of catechin and epicatechin increased following the increase in the adelgid population number. An increase in content occurred also in flavanonols ampelopsin and taxifolin, while the content of the flavonol kaempferol decreased as the population number of A. laricis increased. The analysis of the anatomical structure of needles showed changes in the shape of the needles, the presence of a thicker layer of epicuticular waxes, and a higher number of mesophyll layers as a result of adelgid feeding.

Comparative Metabolic Defense Responses of Three Tree Species to the Supplemental Feeding Behavior of Anoplophora glabripennis

Elaeagnus angustifolia L. can attract adult Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky), and kill their offspring by gum secretion in oviposition scars. This plant has the potential to be used as a dead-end trap tree for ALB management. However, there is a limited understanding of the attraction ability and biochemical defense response of E. angustifolia to ALB. In this study, we conducted host selection experiments with ALB and then performed physiological and biochemical assays on twigs from different tree species before and after ALB feeding. We analyzed the differential metabolites using the liquid chromatograph-mass spectrometer method. The results showed that ALB's feeding preference was E. angustifolia > P.× xiaohei var. gansuensis > P. alba var. pyramidalis. After ALB feeding, the content of soluble sugars, soluble proteins, flavonoids, and tannins decreased significantly in all species. In three comparison groups, a total of 492 differential metabolites were identified (E. angustifolia:195, P.× xiaohei var. gansuensis:255, P. alba var. pyramidalis:244). Differential metabolites were divided into overlapping and specific metabolites for analysis. The overlapping differential metabolites 7-isojasmonic acid, zerumbone, and salicin in the twigs of three tree species showed upregulation after ALB feeding. The specific metabolites silibinin, catechin, and geniposide, in E. angustifolia, significantly increased after being damaged. Differential metabolites enriched in KEGG pathways indicated that ALB feeding activated tyrosine metabolism and the biosynthesis of phenylpropanoids in three tree species, with a particularly high enrichment of differential metabolites in the flavonoid biosynthesis pathway in E. angustifolia. This study provides the metabolic defense strategies of different tree species against ALB feeding and proposes candidate metabolites that can serve as metabolic biomarkers, potentially offering valuable insights into using E. angustifolia as a control measure against ALB.

Genotypic Variation and Potential Mechanisms of Resistance against Multiple Insect Herbivores in Cranberries

Plant genotypes often exhibit varying resistance levels to herbivores. However, the impact of this genotypic variation on resistance against multiple herbivores remains poorly understood, especially in crops undergoing recent process of domestication. To address this gap, we studied the magnitude and mechanism of resistance in 12 cranberry (Vaccinium macrocarpon) genotypes to three leaf-chewing herbivores - Sparganothis fruitworm (Sparganothis sulfureana), spotted fireworm (Choristoneura parallela), and spongy moth (Lymantria dispar) - along a domestication gradient (native 'wild' genotypes, 'early hybrid' genotypes, and 'modern hybrid' genotypes). Like cranberries, S. sulfureana and C. parallela are native to the United Sates, while L. dispar is an invasive pest. We measured the survival and growth of larvae on each genotype, as well as variation in plant performance (height and biomass) and leaf defensive chemical traits (C/N ratio, total phenolics, total proanthocyanidins, and flavonols levels) in these genotypes to elucidate potential resistance mechanisms. We found differences in C. parallela and L. dispar larval performance across genotypes, with larvae performing better on the modern hybrid genotypes, while S. sulfureana showed no differences. Morphological and chemical traits varied among genotypes, with total phenolics being the only trait correlated with C. parallela and L. dispar larval performance. Notably, the wild genotypes 'McFarlin' and 'Potter' had higher total phenolics and were more resistant to both herbivores than the modern hybrids 'Demoranville' and 'Mullica Queen.' This research contributes to a comprehensive understanding of the impact of crop domestication on multiple insect herbivores, offering insights for future breeding efforts to enhance host-plant resistance against agricultural pests.

Herbivory by Leaf-Cutting Ants: Exploring the Jasmonate Response in Host and Non-Host Plants

Leaf-cutting ants (Formicidae; Atta spp., Acromyrmex spp.) cut off pieces of leaves and other plant tissue and feed it to their symbiotic fungi. As this foraging behavior poses an imminent threat to agriculture, leaf-cutting ants are considered as pests of huge ecologically and economically importance. Consequently, research on leaf-cutting ants focused on their foraging decisions and interactions with their cultivated symbiotic fungi, whereas their effect on the attacked plants, apart from the loss of plant tissue, remains largely unknown. In this study, we investigated the consequences of an attack by leaf-cutting ants and analyzed the plants' defense responses in comparison to chewing caterpillars and mechanical damage. We found that an attack by leaf-cutting ants induces the production of jasmonates in several host and non-host plant species (Arabidopsis thaliana, Vicia faba, Phaseolus lunatus, Tococa quadrialata). Additionally, we showed in the natural host plant lima bean (P. lunatus) that leaf-cutting ant damage immediately leads to the emission of typical herbivory-induced plant volatiles, including green leaf volatiles and terpenoids. Further data exploration revealed clear differences in the defense-related phytohormone profile in plant species of Neotropical and Eurasian origin. Taken together, we show that leaf-cutting ant infestation and their way of clipping the plants' tissues induce jasmonate and jasmonates-mediated responses and do not differ from those to mechanical injury or larval feeding.

Constitutive Level of Specialized Secondary Metabolites Affects Plant Phytohormone Response to Above- and Belowground Herbivores

Plants defend themselves chemically against herbivory through secondary metabolites and phytohormones. Few studies have investigated how constitutive variation in secondary metabolites contributes to systemic herbivory response. We hypothesized that plants with lower constitutive defenses would induce a stronger phytohormone response to spatially separated herbivory than plants with high constitutive defense. We used growth chamber bioassays to investigate how aboveground herbivory by Colorado potato beetle (Leptinotarsa decemlineata, CPB) and belowground herbivory by northern root-knot nematode (Meloidogyne hapla, RKN) altered phytohormones and glycoalkaloids in roots and shoots of two lines of wild potato (Solanum chacoense). These lines had different constitutive levels of chemical defense, particularly leptine glycoalkaloids, which are only present in aboveground tissues. We also determined how these differences influenced the preference and performance of CPB. The susceptible wild potato line responded to aboveground damage by CPB through induction of jasmonic acid (JA) and OPDA. However, when challenged by both RKN and CPB, the susceptible line retained high levels of JA, but not OPDA. Beetles gained more mass after feeding on the susceptible line compared to the resistant line, but were not affected by nematode presence. Belowground, JA, JA-Isoleucine, and OPDA were higher in the resistant line compared to the susceptible line, and some compounds demonstrated response to local herbivory. In contrast, the susceptible line did not induce phytohormone defenses belowground. These findings allow us to predict that constitutive level of defense may influence the threshold of herbivory that may lead to plant-mediated effects on spatially separated herbivores.

Metabolic and Molecular Insights Into Nicotiana benthamiana Trichome Exudates: An Ammunition Depot for Plant Resistance Against Insect Pests

Nicotiana benthamiana, a widely acknowledged laboratory model plant for molecular studies, exhibits lethality to certain insect pests and can serve as a dead-end trap plant for pest control in the field. However, the underlying mechanism of N. benthamiana's resistance against insects remains unknown. Here, we elucidate that the lethal effect of N. benthamiana on the whitefly Bemisia tabaci arises from the toxic glandular trichome exudates. By comparing the metabolite profiles of trichome exudates, we found that 51 metabolites, including five O-acyl sugars (O-AS) with medium-chain acyl moieties, were highly accumulated in N. benthamiana. Silencing of two O-AS biosynthesis genes, branched-chain keto acid dehydrogenase (BCKD) and Isopropyl malate synthase-C (IPMS-C), significantly reduced the O-AS levels in N. benthamiana and its resistance against whiteflies. Additionally, we demonstrated that the higher expression levels of BCKD and IPMS-C in the trichomes of N. benthamiana contribute to O-AS synthesis and consequently enhance whitefly resistance. Furthermore, overexpression of NbBCKD and NbIPMS-C genes in the cultivated tobacco Nicotiana tabacum enhanced its resistance to whiteflies. Our study revealed the metabolic and molecular mechanisms underlying the lethal effect of N. benthamiana on whiteflies and presents a promising avenue for improving whitefly resistance.

Leafhopper salivary carboxylesterase suppresses JA-Ile synthesis to facilitate initial arbovirus transmission in rice phloem

Plant jasmonoyl-L-isoleucine (JA-Ile) is a major defense signal against insect feeding, but whether or how insect salivary effectors suppress JA-Ile synthesis and thus facilitate viral transmission in the plant phloem remains elusive. Insect carboxylesterases (CarEs) are the third major family of detoxification enzymes. Here, we identify a new leafhopper CarE, CarE10, that is specifically expressed in salivary glands and is secreted into the rice phloem as a saliva component. Leafhopper CarE10 directly binds to rice jasmonate resistant 1 (JAR1) and promotes its degradation by the proteasome system. Moreover, the direct association of CarE10 with JAR1 clearly impairs JAR1 enzyme activity for conversion of JA to JA-Ile in an in vitro JA-Ile synthesis system. A devastating rice reovirus activates and promotes the co-secretion of virions and CarE10 via virus-induced vesicles into the saliva-storing salivary cavities of the leafhopper vector and ultimately into the rice phloem to establish initial infection. Furthermore, a virus-mediated increase in CarE10 secretion or overexpression of CarE10 in transgenic rice plants causes reduced levels of JAR1 and thus suppresses JA-Ile synthesis, promoting host attractiveness to insect vectors and facilitating initial viral transmission. Our findings provide insight into how the insect salivary protein CarE10 suppresses host JA-Ile synthesis to promote initial virus transmission in the rice phloem.

Phenylalanine treatment induces tomato resistance to Tuta absoluta via increased accumulation of benzenoid/phenylpropanoid volatiles serving as defense signals

Tuta absoluta ("leafminer"), is a major pest of tomato crops worldwide. Controlling this insect is difficult due to its efficient infestation, rapid proliferation, and resilience to changing weather conditions. Furthermore, chemical pesticides have only a short-term effect due to rapid development of T. absoluta strains. Here, we show that a variety of tomato cultivars, treated with external phenylalanine solutions exhibit high resistance to T. absoluta, under both greenhouse and open field conditions, at different locations. A large-scale metabolomic study revealed that tomato leaves absorb and metabolize externally given Phe efficiently, resulting in a change in their volatile profile, and repellence of T. absoluta moths. The change in the volatile profile is due to an increase in three phenylalanine-derived benzenoid phenylpropanoid volatiles (BPVs), benzaldehyde, phenylacetaldehyde, and 2-phenylethanol. This treatment had no effect on terpenes and green leaf volatiles, known to contribute to the fight against insects. Phe-treated plants also increased the resistance of neighboring non-treated plants. RNAseq analysis of the neighboring non-treated plants revealed an exclusive upregulation of genes, with enrichment of genes related to the plant immune response system. Exposure of tomato plants to either benzaldehyde, phenylacetaldehyde, or 2-phenylethanol, resulted in induction of genes related to the plant immune system that were also induced due to neighboring Phe-treated plants. We suggest a novel role of phenylalanine-derived BPVs as mediators of plant-insect interactions, acting as inducers of the plant defense mechanisms.

Genome-Wide Transcriptomic and Metabolomic Analyses Unveiling the Defence Mechanisms of Populus tremula against Sucking and Chewing Insect Herbivores

Plants and insects coevolved as an evolutionarily successful and enduring association. The molecular arms race led to evolutionary novelties regarding unique mechanisms of defence and detoxification in plants and insects. While insects adopt mechanisms to conquer host defence, trees develop well-orchestrated and species-specific defence strategies against insect herbivory. However, current knowledge on the molecular underpinnings of fine-tuned tree defence responses against different herbivore insects is still restricted. In the current study, using a multi-omics approach, we unveiled the defence response of Populus tremula against aphids (Chaitophorus populialbae) and spongy moths (Lymantria dispar) herbivory. Comparative differential gene expression (DGE) analyses revealed that around 272 and 1203 transcripts were differentially regulated in P. tremula after moth and aphid herbivory compared to uninfested controls. Interestingly, 5716 transcripts were differentially regulated in P. tremula between aphids and moth infestation. Further investigation showed that defence-related stress hormones and their lipid precursors, transcription factors, and signalling molecules were over-expressed, whereas the growth-related counterparts were suppressed in P. tremula after aphid and moth herbivory. Metabolomics analysis documented that around 37% of all significantly abundant metabolites were associated with biochemical pathways related to tree growth and defence. However, the metabolic profiles of aphid and moth-fed trees were quite distinct, indicating species-specific response optimization. After identifying the suitable reference genes in P. tremula, the omics data were further validated using RT-qPCR. Nevertheless, our findings documented species-specific fine-tuning of the defence response of P. tremula, showing conservation on resource allocation for defence overgrowth under aphid and moth herbivory. Such findings can be exploited to enhance our current understanding of molecular orchestration of tree responses against herbivory and aid in developing insect pest resistance P. tremula varieties.

Plant, pest and predator interplay: tomato trichomes effects on Tetranychus urticae (Koch) and the predatory mite Typhlodromus (Anthoseius) recki Wainstein

Trichomes are well-known efficient plant defense mechanisms to limit arthropod herbivory, especially in Solanaceae. The present study aims to evaluate the impact of trichome types on the development, survival and dispersal of Tetranychus urticae, and the phytoseiid predatory mite Typhlodromus (Anthoseius) recki. Six Solanum lycopersicum cultivars and two wild Solanum species, S. cheesmaniae and S. peruvianum, presenting contrasting densities and types of trichomes, were considered. Cultivars and species were characterized by counting each trichome type on leaves, petioles and stems. Mites stuck on petiole and stem and alive mites on the leaflet used for mite release and in the whole plant were counted three weeks after T. urticae plant infestation. Tetranychus urticae settlement and dispersal were differently affected by trichomes. Trichome types V and VI did not affect settlement and dispersal, whereas trichome types I and IV on the petiole had the highest impacton mites. Trichomes on leaves slightly affected mite establishment, there appears to be a repellent effect of trichome types I and IV. The low densities of both T. urticae and its predator detected for the cv. Lancaster could not be clearly associated to the trichome types here considered. The predator did not seem to be affected by plant characteristics, but rather by T. urticae numbers on the plant. The trichome traits unfavorable to T. urticae, did not affect the predator which showed high efficiency to control this pest on all the plant genotypes considered, but at a favorable predator:prey ratio (1:1). Altogether, these results are encouraging for the use of T. (A.) recki as a biological control agent of T. urticae regardless of the trichome structure of the tomato cultivars, but other conditions should be tested to conclude on practical implementations.

Salivary gland transcriptomics of the cotton aphid Aphis gossypii and comparative analysis with other sap-sucking insects

Aphids are sap-sucking insects responsible for crop losses and a severe threat to crop production. Proteins in the aphid saliva are integral in establishing an interaction between aphids and plants and are responsible for host plant adaptation. The cotton aphid, Aphis gossypii (Hemiptera: Aphididae) is a major pest of Gossypium hirsutum. Despite extensive studies of the salivary proteins of various aphid species, the components of A. gossypii salivary glands are unknown. In this study, we identified 123,008 transcripts from the salivary gland of A. gossypii. Among those, 2933 proteins have signal peptides with no transmembrane domain known to be secreted from the cell upon feeding. The transcriptome includes proteins with more comprehensive functions such as digestion, detoxification, regulating host defenses, regulation of salivary glands, and a large set of uncharacterized proteins. Comparative analysis of salivary proteins of different aphids and other insects with A. gossypii revealed that 183 and 88 orthologous clusters were common in the Aphididae and non-Aphididae groups, respectively. The structure prediction for highly expressed salivary proteins indicated that most possess an intrinsically disordered region. These results provide valuable reference data for exploring novel functions of salivary proteins in A. gossypii with their host interactions. The identified proteins may help develop a sustainable way to manage aphid pests.

Post-ingestive stability of a mulberry Kunitz-type protease inhibitor MnKTI-1 in the digestive lumen of silkworm: dual inhibition towards α-amylase and serine protease

BACKGROUND

Adaptation of specialist insects to their host plants and defense responses of plants to phytophagous insects have been extensively recognized while the dynamic interaction between these two events has been largely underestimated. Here, we provide evidence for characterization of an unrevealed dynamic interaction mode of digestive enzymes of specialist insect silkworm and inhibitor of its host plant mulberry tree.

RESULTS

MnKTI-1, a mulberry Kunitz-type protease inhibitor, whose messenger RNA (mRNA) transcription and protein expression in mulberry leaf were severely triggered and up-regulated by tens of times in a matter of hours in response to silkworm, Bombyx mori, and other mulberry pest insects, suggesting a quick response and broad spectrum to insect herbivory. MnKTI-1 proteins were detected in gut content and frass of specialist B. mori, and exhibited significant post-ingestive stability. Recombinant refolded MnKTI-1 (rMnKTI-1) displayed binding affinity to digestive enzymes and a dual inhibitory activity to α-amylase BmAmy and serine protease BmSP2956 in digestive juice of silkworm. Moreover, data from in vitro assays proved that the inhibition of recombinant rMnKTI-1 to BmAmy can be reverted by pre-incubation with BmSP15920, an inactivated silkworm digestive protease that lack of complete catalytic triad.

CONCLUSION

These findings demonstrate that mulberry MnKTI-1 has the potential to inhibit the digestive enzyme activities of its specialist insect herbivore silkworm, whereas this insect may employ inactivated proteases to block protease inhibitors to accomplish food digestion. The current work provides an insight to better understand the interacting mode between host plant Kunitz protease inhibitors and herbivorous insect digestive enzymes. © 2024 Society of Chemical Industry.

A protocol for increased throughput phenotyping of plant resistance to the pollen beetle

BACKGROUND

Improving crop resistance to insect herbivores is a major research objective in breeding programs. Although genomic technologies have increased the speed at which large populations can be genotyped, breeding programs still suffer from phenotyping constraints. The pollen beetle (Brassicogethes aeneus) is a major pest of oilseed rape for which no resistant cultivar is available to date, but previous studies have highlighted the potential of white mustard as a source of resistance and introgression of this resistance appears to be a promising strategy. Here we present a phenotyping protocol allowing mid-throughput (i.e., increased throughput compared to current methods) acquisition of resistance data, which could then be used for genetic mapping of QTLs.

RESULTS

Contrasted white mustard genotypes were selected from an initial field screening and then evaluated for their resistance under controlled conditions using a standard phenotyping method on entire plants. We then upgraded this protocol for mid-throughput phenotyping, by testing two alternative methods. We found that phenotyping on detached buds did not provide the same resistance contrasts as observed with the standard protocol, in contrast to the phenotyping protocol with miniaturized plants. This protocol was then tested on a large panel composed of hundreds of plants. A significant variation in resistance among genotypes was observed, which validates the large-scale application of this new phenotyping protocol.

CONCLUSION

The combination of this mid-throughput phenotyping protocol and white mustard as a source of resistance against the pollen beetle offers a promising avenue for breeding programs aiming to improve oilseed rape resistance. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Small but strong: herbivory by sap-feeding insect reduces plant progeny growth but enhances direct and indirect anti-herbivore defenses

The transmission of resistance traits to herbivores across subsequent generations is an important strategy employed by plants to enhance their fitness in environments with high herbivore pressure. However, our understanding of the impact of maternal herbivory on direct and indirect induced chemical defenses of progeny, as well as the associated costs, is currently limited to herbivory by leaf-chewing insects. In this study, we investigated the transgenerational effects of a sap-feeding insect, the green peach aphid Myzus persicae, on direct and indirect chemical defenses of bell pepper plants (Capsicum annuum), and whether the effects entail costs to plant growth. Aphid herbivory on parental plants led to a reduced number of seeds per fruit, which exhibited lower germination rates and produced smaller seedlings compared to those from non-infested parental plants. In contrast, the progeny of aphid-infested plants were less preferred as hosts by aphids and less suitable than the progeny of non-infested plants. This enhanced resistance in the progeny of aphid-infested plants coincided with elevated levels of both constitutive and herbivore-induced total phenolic compounds, compared to the progeny of non-infested plants. Furthermore, the progeny of aphid-infested plants emitted herbivore-induced plant volatiles (HIPVs) that were more attractive to the aphid parasitoid Aphidius platensis than those emitted by the progeny of non-infested plants. Our results indicate that herbivory by sap-feeding insect induces transgenerational resistance on progeny bell pepper plants, albeit at the expense of vegetative growth.

Defense strategies and associated phytohormonal regulation in Brassica plants in response to chewing and sap-sucking insects

Plants have evolved distinct defense strategies in response to a diverse range of chewing and sucking insect herbivory. While chewing insect herbivores, exemplified by caterpillars and beetles, cause visible tissue damage and induce jasmonic acid (JA)-mediated defense responses, sucking insects, such as aphids and whiteflies, delicately tap into the phloem sap and elicit salicylic acid (SA)-mediated defense responses. This review aims to highlight the specificity of defense strategies in Brassica plants and associated underlying molecular mechanisms when challenged by herbivorous insects from different feeding guilds (i.e., chewing and sucking insects). To establish such an understanding in Brassica plants, the typical defense responses were categorized into physical, chemical, and metabolic adjustments. Further, the impact of contrasting feeding patterns on Brassica is discussed in context to unique biochemical and molecular modus operandi that governs the resistance against chewing and sucking insect pests. Grasping these interactions is crucial to developing innovative and targeted pest management approaches to ensure ecosystem sustainability and Brassica productivity.

Salicylic acid inducing the expression of maize anti-insect gene SPI: a potential control strategy for Ostrinia furnacalis

BACKGROUND

Due to being rooted in the ground, maize (Zea mays L.) is unable to actively escape the attacks of herbivorous insects such as the Asian corn borer (Ostrinia furnacalis). In contrast to the passive damage, plants have evolved defense mechanisms to protect themselves from herbivores. Salicylic acid, a widely present endogenous hormone in plants, has been found to play an important role in inducing plant resistance to insects. In this study, we screened and identified the insect resistance gene SPI, which is simultaneously induced by SA and O. furnacalis feeding, through preliminary transcriptome data analysis. The functional validation of SPI was carried out using bioinformatics, RT-qPCR, and heterologous expression protein feeding assays.

RESULTS

Both SA and O. furnacalis treatment increased the expression abundance of SA-synthesis pathway genes and SPI in three maize strains, and the upregulation of SPI was observed strongly at 6 hours post-treatment. The expression of SPI showed a temporal relationship with SA pathway genes, indicating that SPI is a downstream defense gene regulated by SA. Protein feeding assays using two different expression vectors demonstrated that the variation in SPI protein activity among different strains is mainly due to protein modifications.

CONCLUSIONS

Our research results indicate that SPI, as a downstream defense gene regulated by SA, is induced by SA and participates in maize's insect resistance. The differential expression levels of SPI gene and protein modifications among different maize strains are one of the reasons for the variation in insect resistance. This study provides new insights into ecological pest control in maize and valuable insights into plant responses to SA-induced insect resistance.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.

Gene expression plasticity facilitates different host feeding in Ips sexdentatus (Coleoptera: Curculionidae: Scolytinae)

Host shift is ecologically advantageous and a crucial driver for herbivore insect speciation. Insects on the non-native host obtain enemy-free space and confront reduced competition, but they must adapt to survive. Such signatures of adaptations can often be detected at the gene expression level. It is astonishing how bark beetles cope with distinct chemical environments while feeding on various conifers. Hence, we aim to disentangle the six-toothed bark beetle (Ips sexdentatus) response against two different conifer defences upon host shift (Scots pine to Norway spruce). We conducted bioassay and metabolomic analysis followed by RNA-seq experiments to comprehend the beetle's ability to surpass two different terpene-based conifer defence systems. Beetle growth rate and fecundity were increased when reared exclusively on spruce logs (alternative host) compared to pine logs (native host). Comparative gene expression analysis identified differentially expressed genes (DEGs) related to digestion, detoxification, transporter activity, growth, signalling, and stress response in the spruce-feeding beetle gut. Transporter genes were highly abundant during spruce feeding, suggesting they could play a role in pumping a wide variety of endogenous and xenobiotic compounds or allelochemicals out. Trehalose transporter (TRET) is also up-regulated in the spruce-fed beetle gut to maintain homeostasis and stress tolerance. RT-qPCR and enzymatic assays further corroborated some of our findings. Taken together, the transcriptional plasticity of key physiological genes plays a crucial role after the host shift and provides vital clues for the adaptive potential of bark beetles on different conifer hosts.

How Plant Toxins Cause Early Larval Mortality in Herbivorous Insects: An Explanation by Modeling the Net Energy Curve

Plants store chemical defenses that act as toxins against herbivores, such as toxic isothiocyanates (ITCs) in Brassica plants, hydrolyzed from glucosinolate (GLS) precursors. The fitness of herbivorous larvae can be strongly affected by these toxins, causing immature death. We modeled this phenomenon using a set of ordinary differential equations and established a direct relationship between feeding, toxin exposure, and the net energy of a larva, where the fitness of an organism is proportional to its net energy according to optimal foraging theory. Optimal foraging theory is widely used in ecology to model the feeding and searching behavior of organisms. Although feeding provides energy gain, plant toxins and foraging cause energy loss for the larvae. Our equations explain that toxin exposure and foraging can sharply reduce larval net energy to zero at an instar. Since herbivory needs energy, the only choice left for a larva is to stop feeding at that time point. If that is significantly earlier than the end of the last instar stage, the larva dies without food. Thus, we show that plant toxins can cause immature death in larvae from the perspective of optimal foraging theory.

Response of cassava (Manihot esculenta Crantz) genotypes to natural infestation by scale insect pest Stictococcus vayssierei Richard (Hemiptera: Stictococcidae)

Cassava is mostly grown for its starchy roots, which ensure food security. However, it is heavily attacked by the African root and tuber scale (ARTS) Stictococcus vayssierei in Central Africa. This pest is a severe constraint to the production of cassava, food and income security for smallholder farmers. Crop resistance development through the selection of varieties with resistant traits against targeted pests is a promising approach to pest control. This study investigated cassava genotypes' response to natural infestation and determined their resistance levels against S. vayssierei. Six cassava genotypes (two local and four improved) were planted in a completely randomized block design with four replicates. Agronomic parameters and ARTS density were evaluated at 3, 6, 9 and 12 months after planting (MAP). Biochemical content was determined on the pith and cortex of 12 MAP aged tuberous roots. As a result, the improved Excel variety recorded the highest scale density per plant with 102.83 ± 4.14 ARTS/P at 9 MAP. At 12 MAP, high activity of total cyanide (69.18 ± 0.88 and 69.16 ± 1.44 mg/kg) and phenylalanine ammonia-lyase (0.142 ± 0.020 and 0.145 ± 0.010 ΔA/min/mg) were observed in the cortex of the tuberous roots of the improved varieties TMS 96/0023 and TMS 92/0057 which were colonized by the lowest ARTS density. The local variety (Douma) had a high content of total phenols (44.87 ± 1.15 µg/g) in the pith. It also produced the highest yield (23.8 ± 2.9 t ha-1). Varieties TMS 96/0023, TMS 92/0057 and Douma may be the most suitable varieties for the control of ARTS stress.

Selection pressure by specialist and generalist insect herbivores leads to optimal constitutive plant defense. A mathematical model

Brassicaceae plants have the glucosinolate-myrosinase defense system, jointly active against herbivory. However, constitutive glucosinolate (GLS) defense is observed to occur at levels that do not deter all insects from feeding. That prompts the question of why Brassicaceae plants have not evolved a higher constitutive defense. The answer may lie in the contrasting relationship between plant defense and host plant preference of specialist and generalist herbivores. GLS content increases a plant's susceptibility to specialist insects. In contrast, generalists are deterred by the plant GLSs. Although GLSs can attract the natural enemies (predators and parasitoids) of these herbivores, enemies can reduce herbivore pressure to some extent only. So, plants can be overrun by specialists if GLS content is too high, whereas generalists can invade the plants if it is too low. Therefore, an optimal constitutive plant defense can minimize the overall herbivore pressure. To explain the optimal defense theoretically, we model the contrasting host selection behavior of insect herbivores and the emergence of their natural enemies by non-autonomous ordinary differential equations, where the independent variable is the plant GLS concentration. From the model, we quantify the optimal amount of GLSs, which minimizes total herbivore (specialists and generalists) pressure. That quite successfully explains the evolution of constitutive defense in plants from the perspective of optimality theory.

The salivary chaperone protein NlDNAJB9 of Nilaparvata lugens activates plant immune responses

The brown planthopper (BPH) Nilaparvata lugens (Stål) is a main pest on rice. It secretes saliva to regulate plant defense responses, when penetrating rice plant and sucking phloem sap through its stylet. However, the molecular mechanisms of BPH salivary proteins regulating plant defense responses remain poorly understood. A N. lugens DNAJ protein (NlDNAJB9) gene was highly expressed in salivary glands, and the knock down of NlDNAJB9 significantly enhanced honeydew excretion and fecundity of the BPH. NlDNAJB9 could induce plant cell death, and the overexpression of NlDNAJB9 gene in Nicotiana benthamiana induced calcium signaling, mitogen-activated protein kinase (MAPK) cascades, reactive oxygen species (ROS) accumulation, jasmonic acid (JA) hormone signaling and callose deposition. The results from different NlDNAJB9 deletion mutants indicated that the nuclear localization of NlDNAJB9 was not necessary to induce cell death. The DNAJ domain was the key region to induce cell death, and the overexpression of DNAJ domain in N. benthamiana significantly inhibited insect feeding and pathogenic infection. NlDNAJB9 might interact indirectly with NlHSC70-3 to regulate plant defense responses. NlDNAJB9 and its orthologs were highly conserved in three planthopper species, and could induce ROS burst and cell death in plants. Our study provides new insights into the molecular mechanisms of insect-plant interactions.

A Diet with Amikacin Changes the Bacteriobiome and the Physiological State of Galleria mellonella and Causes Its Resistance to Bacillus thuringiensis

Environmental pollution with antibiotics can cause antibiotic resistance in microorganisms, including the intestinal microbiota of various insects. The effects of low-dose aminoglycoside antibiotic (amikacin) on the resident gut microbiota of Galleria mellonella, its digestion, its physiological parameters, and the resistance of this species to bacteria Bacillus thuringiensis were investigated. Here, 16S rDNA analysis revealed that the number of non-dominant Enterococcus mundtii bacteria in the eighteenth generation of the wax moth treated with amikacin was increased 73 fold compared to E. faecalis, the dominant bacteria in the native line of the wax moth. These changes were accompanied by increased activity of acidic protease and glutathione-S-transferase in the midgut tissues of larvae. Ultra-thin section electron microscopy detected no changes in the structure of the midgut tissues. In addition, reduced pupa weight and resistance of larvae to B. thuringiensis were observed in the eighteenth generation of the wax moth reared on a diet with amikacin. We suggest that long-term cultivation of wax moth larvae on an artificial diet with an antibiotic leads to its adaptation due to changes in both the gut microbiota community and the physiological state of the insect organism.

Defensive furofuran lignans localized to the oil cells of Neocinnamomum delavayi and their metabolism by a specialist insect

Neocinnamomum delavayi (Lauraceae) leaves with abundant oil cells are seldom attacked by insects, but their chemical constituent and biological function remain obscure. Three furofuran lignans, including (+)-eudesmin (3), (+)-magnolin (4), and demethoxyaschantin (5), were identified to be the major specialized metabolites in the oil cells of N. delavayi leaves through laser microdissection coupled with NMR analysis. Compounds 3 and 4 exhibited obvious antifeedant activity against a generalist insect Spodoptera exigua, and their natural contents in the leaves could effectively defend against generalist insects. Intriguingly, three specific metabolites 9-11, the O-demethylation derivates of compounds 3-5, were identified from a native specialist insect Dindica polyphaenaria feeding with N. delavayi leaves, implying an adaptation mechanism of specialist insects to plant defensive compounds. The results revealed a chemical connection between plants and insects, which would contribute to our understanding of plant-insect interaction and insect management.

Four-Chlorophenoxyacetic Acid Treatment Induces the Defense Resistance of Rice to White-Backed Planthopper Sogatella furcifera

Chemical elicitors can increase plant defense against herbivorous insects and pathogens. The use of synthetic chemical elicitors is likely to be an alternative to traditional pesticides for crop pest control. However, only a few synthetic chemicals are reported to protect plants by regulating signaling pathways, increasing the levels of defense metabolites and interfering with insect feeding. Here, we found that the exogenous application of a phenoxycarboxylic compound, 4-chlorophenoxyacetic acid (4-CPA), can induce chemical defenses to protect rice plants from white-backed planthoppers (WBPH, Sogatella furcifera). Four-CPA was rapidly taken up by plant roots and degraded to 4-chlorophenol (4-CP). Four-CPA treatment modulated the activity of peroxidase (POD) and directly induced the deposition of lignin-like polymers using hydrogen peroxide (H2O2) as the electron acceptor. The polymers, which are thought to prevent the planthopper's stylet from reaching the phloem, were broken down by WBPH nymphs. Meanwhile, 4-CPA increased the levels of flavonoids and phenolamines (PAs). The increased flavonoids and PAs, together with the degradation product of the polymers, avoided nymphal feeding and prolonged the nymphal period for 1 day. These results indicate that 4-CPA has the potential to be used as a chemical elicitor to protect rice from planthoppers. Moreover, these findings also open a pathway for molecule structure design of phenoxycarboxylic compounds as chemical elicitors.

Combined Omics Approaches Reveal Distinct Mechanisms of Resistance and/or Susceptibility in Sugar Beet Double Haploid Genotypes at Early Stages of Beet Curly Top Virus Infection

Sugar beet is susceptible to Beet curly top virus (BCTV), which significantly reduces yield and sugar production in the semi-arid growing regions worldwide. Sources of genetic resistance to BCTV is limited and control depends upon insecticide seed treatments with neonicotinoids. Through double haploid production and genetic selection, BCTV resistant breeding lines have been developed. Using BCTV resistant (R) [KDH13; Line 13 and KDH4-9; Line 4] and susceptible (S) [KDH19-17; Line 19] lines, beet leafhopper mediated natural infection, mRNA/sRNA sequencing, and metabolite analyses, potential mechanisms of resistance against the virus and vector were identified. At early infection stages (2- and 6-days post inoculation), examples of differentially expressed genes highly up-regulated in the 'R' lines (vs. 'S') included EL10Ac5g10437 (inhibitor of trypsin and hageman factor), EL10Ac6g14635 (jasmonate-induced protein), EL10Ac3g06016 (ribosome related), EL10Ac2g02812 (probable prolyl 4-hydroxylase 10), etc. Pathway enrichment analysis showed differentially expressed genes were predominantly involved with peroxisome, amino acids metabolism, fatty acid degradation, amino/nucleotide sugar metabolism, etc. Metabolite analysis revealed significantly higher amounts of specific isoflavonoid O-glycosides, flavonoid 8-C glycosides, triterpenoid, and iridoid-O-glycosides in the leaves of the 'R' lines (vs. 'S'). These data suggest that a combination of transcriptional regulation and production of putative antiviral metabolites might contribute to BCTV resistance. In addition, genome divergence among BCTV strains differentially affects the production of small non-coding RNAs (sncRNAs) and small peptides which may potentially affect pathogenicity and disease symptom development.

Genotypic variation in field-grown maize eliminates trade-offs between resistance, tolerance and growth in response to high pressure from the Asian corn borer

Insect herbivory challenges plant survival, and coordination of the interactions between growth, herbivore resistance/tolerance is a key problem faced by plants. Based on field experiments into resistance to the Asian corn borer (ACB, Ostrinia furnacalis), we selected 10 inbred maize lines, of which five were resistant and five were susceptible to ACB. We conducted ACB larval bioassays, analysed defensive chemicals, phytohormones, and relative gene expression using RNA-seq and qPCR as well as agronomic traits, and found resistant lines had weaker inducibility, but were more resistant after ACB attack than susceptible lines. Resistance was related to high levels of major benzoxazinoids, but was not related to induced levels of JA or JA-Ile. Following combination analyses of transcriptome, metabolome and larval performance data, we discovered three benzoxazinoids biosynthesis-related transcription factors, NAC60, WRKY1 and WRKY46. Protoplast transformation analysis suggested that these may regulate maize defence-growth trade-offs by increasing levels of benzoxazinoids, JA and SA but decreasing IAA. Moreover, the resistance/tolerance-growth trade-offs were not observed in the 10 lines, and genotype-specific metabolic and genetic features probably eliminated the trade-offs. This study highlights the possibility of breeding maize varieties simultaneously with improved defences and higher yield under complex field conditions.

Regional Pollination Activity by Moth Migration in Athetis lepigone

Nocturnal moths (Lepidoptera) are important pollinators of a wide range of plant species. Understanding the foraging preferences of these insects is essential for their scientific management. However, this information is lacking for most moth species. The present study was therefore conducted to delineate the host plant feeding and pollination ranges of an agriculturally important nocturnal moth species Athetis lepigone by identifying the pollen species adhering to their bodies during long-distance migration. Pollen grains were dislodged from 1871 A. lepigone migrants captured on Beihuang Island in the Bohai Strait between 2020 and 2021. This region is a key seasonal migration pathway for A. lepigone in northern China. Almost 20% of all moths sampled harbored pollens, providing direct evidences that this moth species may serve as pollinators. Moreover, at least 39 pollen taxa spanning 21 plant families and 31 genera were identified, with a preference for Asteraceae, Amaranthaceae, and Pinaceae. Additionally, the pollen adherence ratios and taxa varied with moth sex, inter-annual changes, and seasonal fluctuations. Most importantly, the pollen taxa were correlated with insect migration stages and indicated that A. lepigone bidirectionally migrates between central China (Shandong, Hebei, and Henan Provinces) and northeastern China (Liaoning Province). Overall, the findings of the present work provide valuable information on the pollination behavior, geographical origins, and pollination regions of A. lepigone moths and could facilitate the design and optimization of efficacious local and regional management strategies for this important insect.

Trade-offs in non-native plant herbivore defences enhance performance

Non-native plants are typically released from specialist enemies but continue to be attacked by generalists, albeit at lower intensities. This reduced herbivory may lead to less investment in constitutive defences and greater investment in induced defences, potentially reducing defence costs. We compared herbivory on 27 non-native and 59 native species in the field and conducted bioassays and chemical analyses on 12 pairs of non-native and native congeners. Non-natives suffered less damage and had weaker constitutive defences, but stronger induced defences than natives. For non-natives, the strength of constitutive defences was correlated with the intensity of herbivory experienced, whereas induced defences showed the reverse. Investment in induced defences correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. To our knowledge, these are the first linkages reported among trade-offs in plant defences related to the intensity of herbivory, allocation to constitutive versus induced defences, and growth.

Comparative Transcriptome Analysis of Defense Response of Potato to Phthorimaea operculella Infestation

The potato tuber moth (PTM), Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), is one of the most destructive pests of potato crops worldwide. Although it has been reported how potatoes integrate the early responses to various PTM herbivory stimuli by accumulatively adding the components, the broad-scale defense signaling network of potato to single stimuli at multiple time points are unclear. Therefore, we compared three potato transcriptional profiles of undamaged plants, mechanically damaged plants and PTM-feeding plants at 3 h, 48 h, and 96 h, and further analyzed the gene expression patterns of a multitude of insect resistance-related signaling pathways, including phytohormones, reactive oxygen species, secondary metabolites, transcription factors, MAPK cascades, plant-pathogen interactions, protease inhibitors, chitinase, and lectins, etc. in the potato under mechanical damage and PTM infestation. Our results suggested that the potato transcriptome showed significant responses to mechanical damage and potato tuber moth infestation, respectively. The potato transcriptome responses modulated over time and were higher at 96 than at 48 h, so transcriptional changes in later stages of PTM infestation may underlie the potato recovery response. Although the transcriptional profiles of mechanically damaged and PTM-infested plants overlap extensively in multiple signaling pathways, some genes are uniquely induced or repressed. True herbivore feeding induced more and stronger gene expression compared to mechanical damage. In addition, we identified 2976, 1499, and 117 genes that only appeared in M-vs-P comparison groups by comparing the transcriptomes of PTM-damaged and mechanically damaged potatoes at 3 h, 48 h, and 96 h, respectively, and these genes deserve further study in the future. This transcriptomic dataset further enhances the understanding of the interactions between potato and potato tuber moth, enriches the molecular resources in this research area and paves the way for breeding insect-resistant potatoes.

Bottom-Up Effects of Drought-Stressed Cotton Plants on Performance and Feeding Behavior of Aphis gossypii

Drought, a major stress for crop plants, is expected to increase in frequency due to climate change. Drought can alter crop growth and levels of secondary plant metabolites, which in turn can affect herbivores, but this latter point is still controversial. This study used three different polyethylene glycol (PEG-6000) levels (0%, 1%, and 3%) to simulate drought stress and evaluated their effects on cotton plants and the impacts on the performance of the cotton aphid Aphis gossypii. Cotton plants under drought stress showed decreased water content, above-ground biomass, and nitrogen content and increased soluble protein, soluble sugar, and tannin contents. Based on analysis of the developmental time and fecundity data from individuals and at the population level, a significantly lower fecundity and population abundance of A. gossypii were detected on cotton plants with drought stress, which supports the "plant vigor hypothesis". The poor development of A. gossypii is possibly related to lower xylem sap and phloem ingestion under drought stress. In addition, the increased tannin content of cotton plants induced by drought and lower detoxification enzyme activities of A. gossypii may have affected the responses of aphids to drought-stressed plants. Overall, the results showed that drought stress altered the physiological characteristics of the cotton plants, resulting in adverse bottom-up effects on cotton aphid performances. This implies that the adoption of drip irrigation under plastic film that can help alleviate drought stress may favor the population growth of cotton aphids.

Chitosan-induced biotic stress tolerance and crosstalk with phytohormones, antioxidants, and other signalling molecules

Several polysaccharides augment plant growth and productivity and galvanise defence against pathogens. Such elicitors have ecological superiority over traditional growth regulators, considering their amplified biocompatibility, biodegradability, bioactivity, non-toxicity, ubiquity, and inexpensiveness. Chitosan is a chitin-derived polysaccharide that has recently been spotlighted among plant scientists. Chitosan supports plant growth and development and protects against microbial entities such as fungi, bacteria, viruses, nematodes, and insects. In this review, we discuss the current knowledge of chitosan's antimicrobial and insecticidal potential with recent updates. These effects are further explored with the possibilities of chitosan's active correspondence with phytohormones such as jasmonic acid (JA), salicylic acid (SA), indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA). The stress-induced redox shift in cellular organelles could be substantiated by the intricate participation of chitosan with reactive oxygen species (ROS) and antioxidant metabolism, including hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, we propose how chitosan could be intertwined with cellular signalling through Ca2+, ROS, nitric oxide (NO), transcription factors (TFs), and defensive gene activation.

Herbivore-Dependent Induced Volatiles in Pear Plants Cause Differential Attractive Response by Lacewing Larvae

Biological control may benefit from the behavioral manipulation of natural enemies using volatile organic compounds (VOCs). Among these, herbivore-induced plant volatiles (HIPVs) provide potential tools for attracting or retaining predators and parasitoids of insect pests. This work aimed to characterize the VOCs emitted by pear plants in response to attack by Cacopsylla bidens (Hemiptera: Psyllidae), a major pest in pear orchards, to compare these with VOCs induced by a leaf chewing insect, Argyrotaenia sphaleropa (Lepidoptera: Tortricidae), and to evaluate the behavioral response of Chrysoperla externa (Neuroptera: Chrysopidae) to HIPVs from pear plants damaged by either herbivore. The results demonstrated that plants damaged by the pear psylla emitted VOC blends with increased amounts of aliphatic aldehydes. Leafroller damage resulted in increased amounts of benzeneacetonitrile, (E)-4,8-dimethylnona-1,3,7-triene, β-ocimene and caryophyllene. In olfactometer bioassays, larvae of C. externa were attracted to herbivore-damaged plants when contrasted with undamaged plants. When plant odors from psylla-damaged were contrasted with those of leafroller-damaged plants, C.externa preferred the former, also showing shorter response lag-times and higher response rates when psylla-damaged plants were present. Our results suggest that pear plants respond to herbivory by modifying their volatile profile, and that psylla-induced volatiles may be used as prey-specific chemical cues by chrysopid larvae. Our study is the first to report HIPVs in pear plants attacked by C. bidens, as well as the attraction of C. externa to psyllid-induced volatiles.

Oviposition Preference and Age-Stage, Two-Sex Life Table Analysis of Spodoptera frugiperda (Lepidoptera: Noctuidae) on Different Maize Varieties

Host plants play an important role in the growth, development, and reproduction of insects. However, only a few studies have reported the effects of maize varieties on the growth and reproduction of S. frugiperda. In this study, a free-choice test was used to evaluate the oviposition preferences of female adults on ten common maize varieties and ten special maize varieties. The population fitness of S. frugiperda on six different maize varieties was also examined using the age-stage, two-sex life table method. The results showed that S. frugiperda oviposited and completed its life cycle across all maize cultivars. Moreover, the S. frugiperda females exhibited a significantly higher oviposition preference on the special maize varieties than on the common maize varieties. The highest number of eggs and egg masses occurred on Baitiannuo and the lowest on Zhengdan 958. The egg + larval stage, preadult, pupal stage, adult, APOP, TPOP, and total longevity of S. frugiperda were significantly shorter on the special maize varieties than on the common maize varieties. The fecundity, oviposition days, pupal weight, and hatching rate of S. frugiperda were significantly higher on the special maize varieties than on the common maize varieties. Specifically, S. frugiperda had the highest fecundity, female, and male pupal weight on Baitiannuo. Moreover, the net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ) of S. frugiperda were the greatest on Baitiannuo, whereas the shortest mean generation time (T) occurred on Zaocuiwang. The lowest R₀, r, and λ, and longest T occurred on Zhengdan 958, suggesting that Zhengdan 958 is a non-preferred host plant compared to the other tested maize varieties. The findings of this study can provide a reference for the rational planting of maize and provide basic scientific information for the management of S. frugiperda.

Egg-Associated Germs Induce Salicylate Defenses but Not Render Plant Against a Global Invasive Fruit Fly Effectively

Germs associated with insect eggs can profoundly mediate interactions between host plants and herbivores, with the potential to coordinate plant physiological reactions with cascading effects on insect fitness. An experimental system was established including the oriental fruit fly (OFF, Bactrocera dorsalis) and tomato to examine the functions of egg-associated germs in mediating plant-herbivore interactions. OFF feeding resulted in significantly increased tannins, flavonoids, amino acids, and salicylic acid in the host tomato. These defensive responses of tomato were induced by the egg-associated germs, including Lactococcus sp., Brevundimonas sp., and Vagococcus sp. Tannins and flavonoids had no significant feedback effects on the pupal weight of OFF, while pupal biomass was significantly decreased by tannins and flavonoids in the germ-free treatment. Metabolome analysis showed that OFF mainly induced metabolic changes in carboxylic acid derivatives. Phenylalanine significantly induced downstream metabolic changes associated with phenylpropanoid accumulation. Finally, we conclude that the effects of egg-associated germs played an important role in facilitating OFF population adaptation and growth by mediating plant defenses, which provides a new paradigm for exploring the interaction of plant-pest and implementing effective pest biocontrol.

Differential defensive and nutritional traits among cultivated tomato and its wild relatives shape their interactions with a specialist herbivore

Cultivated tomato presented lower constitutive volatiles, reduced morphological and chemical defenses, and increased leaf nutritional quality that affect its resistance against the specialist herbivore Tuta absoluta compared to its wild relatives. Plant domestication process has selected desirable agronomic attributes that can both intentionally and unintentionally compromise other important traits, such as plant defense and nutritional value. However, the effect of domestication on defensive and nutritional traits of plant organs not exposed to selection and the consequent interactions with specialist herbivores are only partly known. Here, we hypothesized that the modern cultivated tomato has reduced levels of constitutive defense and increased levels of nutritional value compared with its wild relatives, and such differences affect the preference and performance of the South American tomato pinworm, Tuta absoluta-an insect pest that co-evolved with tomato. To test this hypothesis, we compared plant volatile emissions, leaf defensive (glandular and non-glandular trichome density, and total phenolic content), and nutritional traits (nitrogen content) among the cultivated tomato Solanum lycopersicum and its wild relatives S. pennellii and S. habrochaites. We also determined the attraction and ovipositional preference of female moths and larval performance on cultivated and wild tomatoes. Volatile emissions were qualitatively and quantitatively different among the cultivated and wild species. Glandular trichomes density and total phenolics were lower in S. lycopersicum. In contrast, this species had a greater non-glandular trichome density and leaf nitrogen content. Female moths were more attracted and consistently laid more eggs on the cultivated S. lycopersicum. Larvae fed on S. lycopersicum leaves had a better performance reaching shorter larval developmental times and increasing the pupal weight compared to those fed on wild tomatoes. Overall, our study documents that agronomic selection for increased yields has altered the defensive and nutritional traits in tomato plants, affecting their resistance to T. absoluta.

Exchange of Microbiomes in Plant-Insect Herbivore Interactions

Prokaryotic and eukaryotic microbial symbiotic communities span through kingdoms. The vast microbial gene pool extends the host genome and supports adaptations to changing environmental conditions. Plants are versatile hosts for the symbionts, carrying microbes on the surface, inside tissues, and even within the cells. Insects are equally abundantly colonized by microbial symbionts on the exoskeleton, in the gut, in the hemocoel, and inside the cells. The insect gut is a prolific environment, but it is selective on the microbial species that enter with food. Plants and insects are often highly dependent on each other and frequently interact. Regardless of the accumulating evidence on the microbiomes of both organisms, it remains unclear how much they exchange and modify each other's microbiomes. In this review, we approach this question from the point of view of herbivores that feed on plants, with a special focus on the forest ecosystems. After a brief introduction to the subject, we concentrate on the plant microbiome, the overlap between plant and insect microbial communities, and how the exchange and modification of microbiomes affects the fitness of each host.

Genome-wide analysis of MYB family in Nicotiana benthamiana and the functional role of the key members in resistance to Bemisia tabaci

MYB transcription factors (TFs) play a key role in plant resistance to abiotic and biotical stresses. However, little is currently known about their involvement in the plant defense to piercing-sucking insects. Here, we studied the MYB TFs that responded to and resisted Bemisia tabaci whitefly in the model plant Nicotiana benthamiana. Firstly, a total of 453 NbMYB TFs in N. benthamiana genome were identified and 182 R2R3-MYB TFs were analyzed for molecular characteristics, phylogenetic analysis, genetic structure, motif composition, and cis-elements. Then, six stress-related NbMYB genes were selected for further study. The expression pattern shows they were highly expressed in mature leaves and intensively induced upon whitefly attack. Combined with bioinformatic analysis, overexpression, β-Glucuronidase (GUS) assay, and virus-induced silencing tests, we determined the transcriptional regulation of these NbMYBs on the genes in lignin biosynthesis and SA-signaling pathways. Meanwhile, we tested the performance of whitefly on plants with increased or silenced NbMYB genes expression and found that NbMYB42, NbMYB107, NbMYB163, and NbMYB423 were resistant to whitefly. Our results contribute to a comprehensive understanding of the MYB TFs in N. benthamiana. Furthermore, our findings will facilitate further studies on the role of MYB TFs in the interaction between plants and piercing-sucking insects.