Mechanisms and ecological consequences of plant defence induction and suppression in herbivore communities

Review: Mechanism of herbivores synergistically metabolizing toxic plants through liver and intestinal microbiota

Interspecific interactions are central to ecological research. Plants produce toxic plant secondary metabolites (PSMs) as a defense mechanism against herbivore overgrazing, prompting their gradual adaptation to toxic substances for tolerance or detoxification. P450 enzymes in herbivore livers bind to PSMs, whereas UDP-glucuronosyltransferase and glutathione S-transferase increase the hydrophobicity of the bound PSMs for detoxification. Intestinal microorganisms such as Bacteroidetes metabolize cellulase and other macromolecules to break down toxic components. However, detoxification is an overall response of the animal body, necessitating coordination among various organs to detoxify ingested PSMs. PSMs undergo detoxification metabolism through the liver and gut microbiota, evidenced by increased signaling processes of bile acids, inflammatory signaling molecules, and aromatic hydrocarbon receptors. In this context, we offer a succinct overview of how metabolites from the liver and gut microbiota of herbivores contribute to enhancing metabolic PSMs. We focused mainly on elucidating the molecular communication between the liver and gut microbiota involving endocrine, immune, and metabolic processes in detoxification. We have also discussed the potential for future alterations in the gut of herbivores to enhance the metabolic effects of the liver and boost the detoxification and metabolic abilities of PSMs.

Brevipalpus yothersi Baker (Tenuipalpidae) development in sweet orange plants is influenced by previous mite infestation and the presence of shelters

Citrus leprosis is the most important viral disease affecting citrus. The disease is caused predominantly by CiLV-C and is transmitted by Brevipalpus yothersi Baker mites. This study brings some insight into the colonization of B. yothersi in citrus [(Citrus × sinensis (L.) Osbeck (Rutaceae)] previously infested by viruliferous or non-viruliferous B. yothersi. It also assesses the putative role of shelters on the behavior of B. yothersi. Expression of PR1 and PR4 genes, markers of plant defense mechanisms, were evaluated by RT-qPCR to correlate the role of the plant hormonal changes during the tri-trophic virus-mite-plant interplay. A previous infestation with either non-viruliferous and viruliferous mites positively influenced oviposition and the number of adult individuals in the resulting populations. Mite populations were higher on branches that had received a previous mite infestation than branches that did not. There was an increase in the expression of PR4, a marker gene in the jasmonic acid (JA) pathway, in the treatment with non-viruliferous mites, indicating a response from the plant to their feeding. Conversely, an induced expression of PR1, a marker gene in the salicylic acid (SA) pathway, was observed mainly in the treatment with viruliferous mites, which suggests the activation of a plant response against the pathogen. The earlier mite infestation, as well as the presence of leprosis lesions and a gypsum mixture as artificial shelters, all fostered the growth of the B. yothersi populations after the second infestation, regardless of the presence or absence of CiLV-C. Furthermore, it is suggested that B. yothersi feeding actually induces the JA pathway in plants. At the same time, the CiLV-C represses the JA pathway and induces the SA pathway, which benefits the mite vector.

The properties and mechanism of action of plant immunomodulators in regulation of immune response - A narrative review focusing on Curcuma longa L., Panax ginseng C. A. Meyer and Moringa oleifera Lam

Herbal treatments have been utilized for millennia to cure a variety of ailments. There are over 20, 000 herbal remedies available to treat cancer and other disease in humans. In Ayurveda, traditional plants having revitalizing and nourishing characteristics are known as "Rasayanas." They have anti-inflammatory, anticancer, anti-microbicidal, antiviral, and immunomodulatory effects on the immune system. Immunomodulation is a mechanism through which the body stimulates, suppresses, or boosts the immune system to maintain homeostasis. Plant-derived immunomodulators are typically phytocompounds, including carbohydrates, phenolics, lipids, alkaloids, terpenoids, organosulfur, and nitrogen-containing chemicals. Immunomodulation activity of phytocompounds from traditional plants is primarily mediated through macrophage activation, phagocytosis stimulation, peritoneal macrophage stimulation, lymphoid cell stimulation, and suppression or enhancement of specific and non-specific cellular immune systems via numerous signalling pathways. Despite extensive research, the precise mechanism of immunomodulation of most traditional plants has not yet been fully elucidated, justifying the need for further experimentation. Therefore, this review describes the immunomodulatory agents from traditional plants such as Curcuma longa L., Panax ginseng C.A. Meyer, and Moringa oleifera Lam, further highlighting the common molecular targets and immunomodulatory mechanism involved in eradicating diseases.

Adaptation of an arthropod predator to a challenging environment is associated with a loss of a genome-wide plastic transcriptional response

BACKGROUND

Structural and chemical plant defence traits may reduce the efficacy of biological control agents in integrated pest management. Breeding programmes have shown arthropod predators' potential to acclimate to challenging host plants. However, whether and how these predators adapt to novel plant environments remain unclear. Using the predatory mite Phytoseiulus persimilis - herbivorous mite Tetranychus urticae system in an experimental evolution setup, we studied the adaptation mechanisms to tomato and cucumber, plants that possess a distinct repertoire of defensive traits.

RESULTS

Experimental evolution experiments on whole plants revealed that allowing P. persimilis to adapt to tomatoes led to an ~100% larger population size. Independent feeding assays showed that tomato- and cucumber-adapted prey reduced predator fecundity. The deleterious effect of ingesting low-quality prey persisted after adaptation of the predator to both cucumber and tomato. We demonstrated that jasmonic acid (JA)-dependent defences reduce prey quality by evaluating predator performance on prey fed on JA defence-deficient tomato plants. Transcriptomic profiling of the replicated P. persimilis lines showed that long-term propagation on tomato and cucumber plants produces distinctive gene-expression levels. Predator adaptation to tomatoes results in the loss of a large transcriptional response, in which predicted cuticle-building rather than detoxification pathways are affected.

CONCLUSION

We showed that the adaptation of predatory arthropods to a novel, challenging plant does not necessarily occur via the prey, but rather through the physical environment of the plant. We provided first insights into the underlying molecular mechanisms. © 2023 Society of Chemical Industry.

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.

Alanine metabolism mediates energy allocation of the brown planthopper to adapt to resistant rice

INTRODUCTION

During the adaptation to host plant resistance, herbivorous insects faced the challenge of overcoming plant defenses while ensuring their own development and reproductive success. To achieve this, a strategic allocation of energy resources for detoxification and ecological fitness maintenance became essential.

OBJECTIVE

This study aimed to elucidate the intricate energy allocation mechanisms involved in herbivore adaptation that are currently poorly understood.

METHODS

The rice Oryza sativa and its monophagous pest, the brown planthopper (BPH), Nilaparvata lugens were used as a model system. An integrated analysis of metabolomes and transcriptomes from different BPH populations were conducted to identify the biomarkers. RNA interference of key genes and exogenous injection of key metabolites were performed to validate the function of biomarkers.

RESULTS

We found that alanine was one of the key biomarkers of BPH adaptation to resistant rice variety IR36. We also found that alanine flow determined the adaptation of BPH to IR36 rice. The alanine aminotransferase (ALT)-mediated alanine transfer to pyruvate was necessary and sufficient for the adaptation. This pathway may be conserved, at least to some extent, in BPH adaptation to multiple rice cultivars with different resistance genes. More importantly, ALT-mediated alanine metabolism is the foundation of downstream energy resource allocation for the adaptation. The adapted BPH population exhibited a significantly higher level of energy reserves in the fat body and ovary when fed with IR36 rice, compared to the unadapted population. This rendered the elevated detoxification in the adapted BPH and their ecological fitness recovery.

CONCLUSION

Overall, our findings demonstrated the crucial role of ALT-mediated alanine metabolism in energy allocation during the adaptation to resistant rice in BPH. This will provide novel knowledge regarding the co-evolutionary mechanisms between herbivores and their host plants.

Emerging role of the crosstalk between gut microbiota and liver metabolome of subterranean herbivores in response to toxic plants

Plant secondary metabolites (PSMs) are a defense mechanism against herbivores, which in turn use detoxification metabolism to process ingested and absorbed PSMs. The feeding environment can cause changes in liver metabolism patterns and the gut microbiota. Here, we compared gut microbiota and liver metabolome to investigate the response mechanism of plateau zokors (Eospalax baileyi) to toxic plant Stellera chamaejasme (SC) in non-SC and SC grassland (-SCG and +SCG). Our results indicated that exposure to SC in the -SCG population increased liver inflammatory markers including prostaglandin (PG) in the Arachidonic acid pathway, while exposure to SC in the +SCG population exhibited a significant downregulation of PGs. Secondary bile acids were significantly downregulated in +SCG plateau zokors after SC treatment. Of note, the microbial taxa Veillonella in the -SCG group was significantly correlated with liver inflammation markers, while Clostridium innocum in the +SCG group had a significant positive correlation with secondary bile acids. The increase in bile acids and PGs can lead to liver inflammatory reactions, suggesting that +SCG plateau zokors may mitigate the toxicity of SC plants by reducing liver inflammatory markers including PGs and secondary bile acids, thereby avoiding liver damage. This provides new insight into mechanisms of toxicity by PSMs and counter-mechanisms for toxin tolerance by herbivores.

Identity Matters: Multiple Herbivory Induces Less Attractive or Repellent Coffee Plant Volatile Emission to Different Natural Enemies

Co-infestations by herbivores, a common situation found in natural settings, can distinctly affect induced plant defenses compared to single infestations. Related tritrophic interactions might be affected through the emission of changed blends of herbivore-induced plant volatiles (HIPVs). In a previous study, we observed that the infestation by red spider mite (Oligonychus ilicis) on coffee plants facilitated the infestation by white mealybug (Planococcus minor), whereas the reverse sequence of infestation did not occur. Here, we examined the involvement of the jasmonate and salicylate pathways in the plant-mediated asymmetrical facilitation between red spider mites and white mealybugs as well as the effect of multiple herbivory on attractiveness to the predatory mite Euseius concordis and the ladybug Cryptolaemus montrouzieri. Both mite and mealybug herbivory led to the accumulation of JA-Ile, JA, and cis-OPDA in plants, although the catabolic reactions of JA-Ile were specifically regulated by each herbivore. Infestation by mites or mealybugs induced the release of novel volatiles by coffee plants, which selectively attracted their respective predators. Even though the co-infestation by mites and mealybugs resulted in a stronger accumulation of JA-Ile, JA and SA than the single infestation treatments, the volatile emission was similar to that of mite-infested or mealybug-infested plants. However, multiple infestation had a negative impact on the attractiveness of HIPVs to the predators, making them less attractive to the predatory mite and a repellent to the ladybug. We discuss the potential underlying mechanisms of the susceptibility induced by mites, and the effect of multiple infestation on each predator.

Research on the Effect of Oriental Fruit Moth Feeding on the Quality Degradation of Chestnut Rose Juice Based on Metabolomics

As a native fruit of China, chestnut rose (Rosa roxburghii Tratt) juice is rich in bioactive ingredients. Oriental fruit moth (OFM), Grapholita molesta (Busck), attacks the fruits and shoots of Rosaceae plants, and its feeding affects the quality and yield of chestnut rose. To investigate the effects of OFM feeding on the quality of chestnut rose juice, the bioactive compounds in chestnut rose juice produced from fruits eaten by OFM were measured. The electronic tongue senses, amino acid profile, and untargeted metabolomics assessments were performed to explore changes in the flavour and metabolites. The results showed that OFM feeding reduced the levels of superoxide dismutase (SOD), tannin, vitamin C, flavonoid, and condensed tannin; increased those of polyphenols, soluble solids, total protein, bitterness, and amounts of bitter amino acids; and decreased the total amino acid and umami amino acid levels. Furthermore, untargeted metabolomics annotated a total of 426 differential metabolites (including 55 bitter metabolites), which were mainly enriched in 14 metabolic pathways, such as flavonoid biosynthesis, tryptophan metabolism, tyrosine metabolism, and diterpenoid biosynthesis. In conclusion, the quality of chestnut rose juice deteriorated under OFM feeding stress, the levels of bitter substances were significantly increased, and the bitter taste was subsequently enhanced.

GARP: A family of glycine and alanine-rich proteins that helps spider mites feed on plants

Spider mites (Tetranychidae) are destructive agricultural pests which have evolved strategies to overcome plant defenses, such as the ability to puncture the leaves of their hosts to feed. The expression of many genes with unknown functions is altered during feeding, but little is known about the role of these genes in plant-mite interactions. Here, we identified 3 novel gene families through analysis of genomic and transcriptomic data from 3 spider mite species. These GARP family genes encode glycine and alanine-rich proteins; they are present in mites (Acariformes) but absent in ticks (Parasitiformes) in the subclass Acari, indicating that these genes have undergone a significant expansion in spider mites and thus play important adaptive roles. Transcriptomic analysis revealed that the expression of GARP genes is strongly correlated with feeding and the transfer to new hosts. We used RNA interference to silence GARP1d in the two-spotted spider mite Tetranychus urticae, which inhibited feeding and egg laying and significantly increased mortality when the mites were transferred to soybean shoots; a similar effect was observed after TuVATPase was silenced. However, no changes in mite mortality were observed after TuGARP1d-silenced mites were placed on an artificial diet, which was different from the effect of TuVATPase silencing. Our results indicate that GARP family members play important roles in mite-plant interactions. Additional studies are needed to clarify the mechanisms underlying these interactions.

Attackers gain the upper hand over plants in the face of rapid global change

Interactions among organisms in natural ecosystems are the foundational underpinnings of nearly all ecological studies. It has never been more important to increase our awareness of how these interactions are altered by human activity, threatening biodiversity and disrupting ecosystem functioning. Much of the historic focus of species conservation has been the preservation of endangered and endemic species at risk from hunting, over-exploitation, and habitat destruction. However, there is increasing evidence that differences between plants and their attacking organisms in the speed and direction of physiological, demographic, and genetic (adaptation) responses to global change are having devastating consequences, resulting in large-scale losses of dominant or abundant plant species, particularly in forest ecosystems. From the elimination in the wild of the American chestnut to the extensive regional damage caused by insect outbreaks in temperate forest ecosystems, these losses of dominant species change the ecological landscape and functioning, and represent important threats to biodiversity at all scales. Introductions due to human activity, range shifts due to climate change, and their combination are the principal drivers behind these profound ecosystem changes. In this Review, we argue that there is an urgent need to increase our recognition and hone our predictive power for how these imbalances may occur. Moreover, we should seek to minimize the consequences of these imbalances in order to ensure the preservation of the structure, function and biodiversity of entire ecosystems, not just rare or highly endangered species.

Comparative bionomics and life table studies of Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) on three cabbage varieties

Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) are important pests of brassica crops, causing significant yield losses on cabbage in Ghana. To inform the development of ecologically sound and sustainable pest management strategies for these pests, their biological and population growth parameters were studied on three cabbage varieties (Oxylus, Fortune, and Leadercross). The study was conducted in a screen house under ambient conditions at 30 ± 1°C and 75 ± 5% RH and 12:12 h photoperiod from September to November 2020. The parameters of the preadult developmental period, survival rates, longevity, reproduction, and life table were evaluated following the female age-specific life table. There were significant differences in the nymphal developmental time, longevity, and fecundity on the cabbage varieties for both aphid species. The highest population growth parameters, net reproductive rate (R₀), intrinsic rate of increase r, and finite rate of increase (λ) were recorded on Oxylus variety for both L. e. pseudobrassicae and M. persicae. The lowest was recorded on Leadercross variety for L.e pseudobrassicae and Fortune for M. persicae. The results from this study suggest that Leadercross is a less suitable host for L. e. pseudobrassicae and Fortune for M. persicae, thus, should be considered as less susceptible varieties for use in primary pest management by small-scale farmers or as a component of an integrated pest management strategy for these pests on cabbage.

Intraspecific variation for host immune activation by the spider mite Tetranychus evansi

Many parasites can interfere with their host's defences to maximize their fitness. Here, we investigated if there is heritable variation in the spider mite Tetranychus evansi for traits associated with how they interact with their host plant. We also determined if this variation correlates with mite fecundity. Tetranychus evansi can interfere with jasmonate (JA) defences which are the main determinant of anti-herbivore immunity in plants. We investigated (i) variation in fecundity in the presence and absence of JA defences, making use of a wild-type tomato cultivar and a JA-deficient mutant (defenseless-1), and (ii) variation in the induction of JA defences, in four T. evansi field populations and 59 inbred lines created from an outbred population originating from controlled crosses of the four field populations. We observed a strong positive genetic correlation between fecundity in the presence (on wild-type) and the absence of JA defences (on defenseless-1). However, fecundity did not correlate with the magnitude of induced JA defences in wild-type plants. Our results suggest that the performance of the specialist T. evansi is not related to their ability to manipulate plant defences, either because all lines can adequately reduce levels of defences, or because they are resistant to them.

Plant viruses induce plant volatiles that are detected by aphid parasitoids

Aphis gossypii (Sternorrhyncha: Aphididae) aphids are vectors of important plant viruses among which cucumber mosaic virus (CMV) and potato virus Y (PVY). Virus-infected plants attract aphid vectors and affect their behavior and growth performance either positively or negatively depending on mode of transmission. Viruses cause changes in the composition and the amount of volatile organic compounds (VOCs) released by the plant that attract aphids. The aphid parasitoid Aphidius colemani (Hymenoptera: Aphelinidae) has been shown to have higher parasitism and survival rates on aphids fed on virus-infected than aphids fed on non-infected plants. We hypothesized that parasitoids distinguish virus-infected plants and are attracted to them regardless of the presence of their aphid hosts. Herein, we examined the attraction of the A. colemani parasitoid to infected pepper plants with each of CMV or PVY without the presence of aphids. The dynamic headspace technique was used to collect VOCs from non-infected and CMV or PVY-infected pepper plants. Identification was performed with gas chromatography-mass spectrometry (GC-MS). The response of the parasitoids on virus-infected vs non-infected pepper plants was tested by Y-tube olfactometer assays. The results revealed that parasitoids displayed a preference to CMV and PVY infected plants compared to those that were not infected.

Identification of Green-Leaf Volatiles Released from Cabbage Palms (Sabal palmetto) Infected with the Lethal Bronzing Phytoplasma

Lethal bronzing (LB) is a fatal infection that affects over 20 species of palms (Arecaceae) and is caused by the phytoplasma 'Candidatus Phytoplasma aculeata'. This pathogen causes significant economic losses to landscape and nursery companies in Florida, USA. Recently, the vector was determined to be the planthopper Haplaxius crudus, which was more abundant on LB-infected palms. Herein, the volatile chemicals emitted from LB-infected palms were characterized using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS). Infected Sabal palmetto were identified and confirmed as positive for LB via quantitative PCR. Healthy controls of each species were selected for comparison. All infected palms exhibited elevated levels of hexanal and E-2-hexenal. Threatened palms showed high releasing concentrations of 3-hexenal and Z-3-hexen-1-ol. The volatiles characterized herein are common green-leaf volatiles (GLVs) emitted by plants under stress. This study considers the first documented case of GLVs in palms attributed to phytoplasma infection. Due to the apparent attraction of LB-infected palms to the vector, one or several of the GLVs identified in this study could serve as a lure for the vector and supplement management programs.

Induction of resistance, enzyme activity, and phytochemicals in canola plants treated with abscisic acid elevated based on nutrient availability: a case study on Brevicoryne brassicae L. (Hemiptera: Aphididae)

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae), is one of the important pests of cruciferous plants throughout the world including Iran. In the present study, we grew cultivated canola plants under different fertilizers or distilled water and sprayed them with 100 µM abscisic acid (ABA) or a control solution (NaOH dissolved in water) to study (i) the antibiosis parameters of B. brassicae on these plants; (ii) the antixenosis of B. brassicae adults on these plants; (iii) the plant's peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activity; and (iv) the plant's total phenolic and glucosinolate content. The results of antibiosis experiments showed that ABA and fertilizers have a profound and negative effect on the performance of B. brassicae. In the antixenosis experiment, control plants attracted a significantly higher number of adult females in comparison to treated plants. Also, B. brassicae had lower performance and preference when they were reared on the ABA-treated fertilized plants with higher levels of phenolic and glucosinolate content. These results prompted us to hypothesize that fertilizers enable canola plants to trigger a higher level of secondary metabolites. Our findings reveal that the type and level of nutrient availability may have different impacts on how the plant regulates its defense mechanisms.

Insect Herbivory on Main Stem Enhances Induced Defense of Primary Tillers in Rice (Oryza sativa L.)

Clonal plants are interconnected to form clonal plant networks with physiological integration, enabling the reassignment as well as sharing of resources among the members. The systemic induction of antiherbivore resistance via clonal integration may frequently operate in the networks. Here, we used an important food crop rice (Oryza sativa), and its destructive pest rice leaffolder (LF; Cnaphalocrocis medinalis) as a model to examine defense communication between the main stem and clonal tillers. LF infestation and MeJA pretreatment on the main stem for two days reduced the weight gain of LF larvae fed on the corresponding primary tillers by 44.5% and 29.0%, respectively. LF infestation and MeJA pretreatment on the main stem also enhanced antiherbivore defense responses in primary tillers: increased levels of a trypsin protease inhibitor, putative defensive enzymes, and jasmonic acid (JA), a key signaling compound involved in antiherbivore induced defenses; strong induction of genes encoding JA biosynthesis and perception; and rapid activation of JA pathway. However, in a JA perception OsCOI RNAi line, LF infestation on main stem showed no or minor effects on antiherbivore defense responses in primary tillers. Our work demonstrates that systemic antiherbivore defense operate in the clonal network of rice plants and JA signaling plays a crucial role in mediating defense communication between main stem and tillers in rice plants. Our findings provide a theoretical basis for the ecological control of pests by using the systemic resistance of cloned plants themselves.

Plant-Mediated Effects of Beneficial Microbes and a Plant Strengthener against Spider Mites in Tomato

The two-spotted spider mite Tetranychus urticae is a polyphagous herbivore with a worldwide distribution, and is a serious pest in tomato and other crops. As an alternative to chemical pesticides, biological control with the release of natural enemies such as predatory mites represent an efficient method to control T. urticae in many crops, but not in tomato. Other biological control agents, such as beneficial microbes, as well as chemical compounds, which can act as plant defense elicitors that confer plant resistance against pests and pathogens, may prove promising biological solutions for the suppression of spider mite populations in tomato. Here, we assessed this hypothesis by recording the effects of a series of fungal and bacterial strains and the plant strengthener acibenzolar-s-methyl for their plant-mediated effects on T. urticae performance in two tomato cultivars. We found significant negative effects on the survival, egg production and spider mite feeding damage on plants inoculated with microbes or treated with the plant strengthener as compared to the control plants. Our results highlight the potential of beneficial microbes and plant strengtheners in spider mite suppression in addition to plant disease control.

Genetic analysis of the tomato russet mite provides evidence of oligophagy and a widespread pestiferous haplotype

Worldwide, the tomato russet mite (TRM), Aculops lycopersici (Eriophyidae), is a key pest on cultivated tomato in addition to infesting other cultivated and wild Solanaceae; however, basic information on TRM supporting effective control strategies is still lacking, mainly regarding its taxonomic status and genetic diversity and structure. As A. lycopersici is reported on different species and genera of host plants, populations associated with different host plants may constitute specialized cryptic species, as shown for other eriophyids previously considered generalists. The main aims of this study were to (i) confirm the TRM taxonomic unity of populations from different host plants and localities as well as the species' oligophagy, and (ii) to advance the understanding of TRM host relationship and invasion history. For this purpose, we evaluated the genetic variability and structure of populations from different host plants along crucial areas of occurrence, including the area of potential origin, based on DNA sequences of mitochondrial (cytochrome c oxidase subunit I) and nuclear (internal transcribed spacer, D2 28S) genomic regions. Specimens from South America (Brazil) and Europe (France, Italy, Poland, The Netherlands) were collected from tomato and other solanaceous species from the genera Solanum and Physalis. Final TRM datasets were composed of 101, 82 and 50 sequences from the COI (672 bp), ITS (553 bp) and D2 (605 bp) regions, respectively. Distributions and frequencies of haplotypes (COI) and genotypes (D2 and ITS1) were inferred; pairwise genetic distance comparisons, and phylogenetic analysis were performed, including Bayesian Inference (BI) combined analysis. Our results showed that genetic divergences for mitochondrial and nuclear genomic regions from TRM associated with different host plants were lower than those observed in other eriophyid taxa, confirming conspecificity of TRM populations and oligophagy of this eriophyid mite. Four haplotypes (cH) were identified from the COI sequences with cH1 being the most frequent, representing 90% of all sequences occurring in all host plants studied (Brazil, France, The Netherlands); the other haplotypes were present exclusively in Brazilian populations. Six variants (I) were identified from the ITS sequences: I-1 was the most frequent (76.5% of all sequences), spread in all countries and associated with all host plants, except S. nigrum. Just one D2 sequence variant was found in all studied countries. The genetic homogeneity among populations highlights the occurrence of a highly invasive and oligophagous haplotype. These results failed to corroborate the hypothesis that differential symptomatology or damage intensity among tomato varieties and solanaceous host plants could be due to the genetic diversity of the associated mite populations. The genetic evidence, along with the history of spread of cultivated tomato, corroborates the hypothesis of a South American origin of TRM.

Plant defense synergies and antagonisms affect performance of specialist herbivores of common milkweed

As a general rule, plants defend against herbivores with multiple traits. The defense synergy hypothesis posits that some traits are more effective when co-expressed with others compared to their independent efficacy. However, this hypothesis has rarely been tested outside of phytochemical mixtures, and seldom under field conditions. We tested for synergies between multiple defense traits of common milkweed (Asclepias syriaca) by assaying the performance of two specialist chewing herbivores on plants in natural populations. We employed regression and a novel application of random forests to identify synergies and antagonisms between defense traits. We found the first direct empirical evidence for two previously hypothesized defense synergies in milkweed (latex by secondary metabolites, latex by trichomes) and identified numerous other potential synergies and antagonisms. Our strongest evidence for a defense synergy was between leaf mass per area and low nitrogen content; given that these "leaf economic" traits typically covary in milkweed, a defense synergy could reinforce their co-expression. We report that each of the plant defense traits showed context-dependent effects on herbivores, and increased trait expression could well be beneficial to herbivores for some ranges of observed expression. The novel methods and findings presented here complement more mechanistic approaches to the study of plant defense diversity and provide some of the best evidence to date that multiple classes of plant defense synergize in their impact on insects. Plant defense synergies against highly specialized herbivores, as shown here, are consistent with ongoing reciprocal evolution between these antagonists.

Density-Dependent Effects of Simultaneous Root and Floral Herbivory on Plant Fitness and Defense

Plants are attacked by multiple herbivores, and depend on a precise regulation of responses to cope with a wide range of antagonists. Simultaneous herbivory can occur in different plant compartments, which may pose a serious threat to plant growth and reproduction. In particular, plants often face co-occurring root and floral herbivory, but few studies have focused on such interactions. Here, we investigated in the field the combined density-dependent effects of root-chewing cebrionid beetle larvae and flower-chewing pierid caterpillars on the fitness and defense of a semiarid Brassicaceae herb. We found that the fitness impact of both herbivore groups was independent and density-dependent. Increasing root herbivore density non-significantly reduced plant fitness, while the relationship between increasing floral herbivore density and the reduction they caused in both seed number and seedling emergence was non-linear. The plant defensive response was non-additive with regard to the different densities of root and floral herbivores; high floral herbivore density provoked compensatory investment in reproduction, and this tolerance response was combined with aboveground chemical defense induction when also root herbivore density was high. Plants may thus prioritize specific trait combinations in response to varying combined below- and aboveground herbivore densities to minimize negative impacts on fitness.

Ectophagous folivores do not profit from rich resources on phylogenetically isolated trees

Resource use by consumers across patches is often proportional to the quantity or quality of the resource within these patches. In folivores, such proportional use of resources is likely to be more efficient when plants are spatially proximate, such as trees forming a forest canopy. However, resources provided by forest-trees are often not used proportionally. We hypothesised that proportional use of resources is reduced when host trees are isolated among phylogenetically distant neighbours that mask olfactory and visual search cues, and reduce folivore movement between trees. Such phylogenetically distant neighbourhoods might sort out species that are specialists, poor dispersers, or have poor access to information about leaf quality. We studied individual oaks, their leaf size and quality, their folivory and abundance of folivores (mostly Lepidopteran ectophages, gallers and miners), and parasitism of folivores. We found that leaf consumption by ectophages hardly increased with increasing leaf size when host trees were phylogenetically isolated. We found a similar effect on host use by parasitoids in 1 year. In contrast, we found no consistent effects in other folivore guilds. Relative abundances of specialists and species with wingless females declined with phylogenetic isolation. However, resource use within each of these groups was inconsistently affected by phylogenetic isolation. We suggest that phylogenetic isolation prevents ectophages from effectively choosing trees with abundant resources, and also sorts out species likely to recruit in situ on their host tree. Trees in phylogenetically distant neighbourhoods may be selected for larger leaves and greater reliance on induced defences.

Unraveling the ameliorative potentials of native lichen Pyxine cocoes (Sw.) Nyl., during COVID 19 phase

Due to the rapid increase in the novel coronavirus virulence, the entire world implemented the practice of lockdown along with the constraint of human movement. The obligation of quarantine halted most of the commercial and industrial movement that prominently disturbed the distinct key environmental parameters directly associated with the plant's and animal's health conditions. In this regard, the research aims to study the sudden shut-off of vehicular activity impact on the naturally growing lichen of the genus Pyxine cocoes. The results showed an increase in the pigments, Fv/Fm ratio, and phytohormones during the lockdown and concurrently the decreasing levels in the post-lockdown period. Interestingly, modulations in the phytohormones occur in the lockdown period as compared to the post-lockdown period. The metals Al, Cr, and Fe show the highest increasing trends in the unlocking period, whereas As, Cd, Pb, Cu, Hg, Mn, and Zn show very little variation during the running and post-lockdown phases. The lichen photosynthetic activity justifies further examination as initial biological indicators of the abrupt environmental variations prompted by such types of atmospheric situations and, to a greater extent, for the risk assessment in the near future. In conclusion, stress-phytohormone and amino acids play a significant role as stress reducers. Although lichens are well known for long environmental assessment, the present study will provide qualitative and quantitative variation in physiochemical changes in the short term and sudden environmental fluctuations. HIGHLIGHTS: • Qualitative and quantitative variation in biochemical parameters in lichen during and post-lockdown period was analyzed. • Stress-phytohormone and amino acids play a significant role as stress reducers. • Selectivity sequence reflection in heavy metal accumulation may be used in future studies.

Sugarcane multitrophic interactions: Integrating belowground and aboveground organisms

Sugarcane is a crop of major importance used mainly for sugar and biofuel production, and many additional applications of its byproducts are being developed. Sugarcane cultivation is plagued by many insect pests and pathogens that reduce sugarcane yields overall. Recently emerging studies have shown complex multitrophic interactions in cultivated areas, such as the induction of sugarcane defense-related proteins by insect herbivory that function against fungal pathogens that commonly appear after mechanical damage. Fungi and viruses infecting sugarcane also modulate insect behavior, for example, by causing changes in volatile compounds responsible for insect attraction or repelling natural vector enemies via a mechanism that increases pathogen dissemination from infected plants to healthy ones. Interestingly, the fungus Fusarium verticillioides is capable of being vertically transmitted to insect offspring, ensuring its persistence in the field. Understanding multitrophic complexes is important to develop better strategies for controlling pathosystems affecting sugarcane and other important crops and highlights the importance of not only studying binary interactions but also adding as many variables as possible to effectively translate laboratory research to real-life conditions.

Herbivory modifies plant symbiont number and impact on host plant performance in the field

Species interactions are a unifying theme in ecology and evolution. Both fields are currently moving beyond their historical focus on isolated pairwise relationships to understand how ecological communities affect focal interactions. Additional species can modify both the number of interactions and the fitness consequences of each interaction (i.e., selection). Although only selection affects the evolution of the focal interaction, the two are often conflated, limiting our understanding of the evolution of multispecies interactions. We manipulated aboveground herbivory on the legume Medicago lupulina in the field and quantified its effect on number of symbionts and the per-symbiont impact on plant performance in two belowground symbioses: mutualistic rhizobia bacteria (Ensifer meliloti) and parasitic root-knot nematodes (Meloidogyne hapla). We found that herbivores modified the number of rhizobia nodules, as well as the benefit per nodule. However, each effect was specific to a distinct herbivory regime: natural herbivory affected nodule number, whereas leafhoppers (Cicadellidae) weakened the per nodule benefit. We did not detect any effect of herbivory on nematode gall number or the cost of infection. Our data demonstrate that distinguishing between symbiont number from the fitness consequences of symbiosis is crucial to accurately infer how pairwise interactions will evolve in a community.

Combined Jasmonic Acid and Ethylene Treatment Induces Resistance Effect in Faba Bean Plants Against Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a serious invasive pest in China. In this study, we determined whether exogenous jasmonic acid (JA) and ethylene (ET) treatments could induce resistance against F. occidentalis in faba bean plants. First, we investigated the effects of different concentrations of JA or ET alone on F. occidentalis and then assessed the effects of optimal concentrations of JA and ET combined. Our results showed that the optimal concertation of JA was 2 mmol/L and ET was 0.5 mmol/L. JA + ET mixture showed the greatest inhibitory effect in terms of oviposition and feeding. JA with ET was found to induce changes in the activities of lipoxygenase (LOX), allene oxide synthase (AOS), polyphenol oxidase (PPO), 1-aminocyclopropane 1-carboxylic acid synthase (ACS), and trypsin inhibitor (TI). This treatment also activated or inhibited the relative expression levels of LOX1, ACO2, ACS2, and AP2/ERF. Treatment of faba bean plants with JA and ET significantly prolonged F. occidentalis development and adult preoviposition period, significantly reduced per-female oviposition, and altered male longevity and offspring demographic parameters. These results indicate that JA with ET can induce defenses against the growth and development of F. occidentalis in faba bean plants.

Enhanced top-down control of herbivore population growth on plants with impaired defences

Herbivore densities can be regulated by bottom-up and top-down forces such as plant defences and natural enemies, respectively. These forces can interact with each other to increase plant protection against herbivores; however, how much complementarity exists between bottom-up and top-down forces still remains to be fully elucidated. Particularly, because plant defences can hinder natural enemies, how these interactions affect herbivore performance and dynamics remains elusive.To address this topic, we performed laboratory and greenhouse bioassays with herbivorous mite pests and predatory mites on mutant tomato plants that lack defensive hairs on stems and leaves. Particularly, we investigated the behaviour and population dynamics of different phytophagous mite species in the absence and presence of predatory mites.We show that predatory mites do not only perform better on tomatoes lacking defensive hairs but also that they can suppress herbivore densities better and faster on these hairless plants. Hence, top-down control of herbivores by natural enemies more than compensated the reduced bottom-up herbivore control by plant defences.Our results lead to the counter-intuitive insight that removing, instead of introducing, plant defence traits can result in superior protection against important pests through biological control. Read the free Plain Language Summary for this article on the Journal blog.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.

Bovine pancreatic trypsin inhibitor and soybean Kunitz trypsin inhibitor: Differential effects on proteases and larval development of the soybean pest Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Pest management is challenged with resistant herbivores and problems regarding human health and environmental issues. Indeed, the greatest challenge to modern agriculture is to protect crops from pests and still maintain environmental quality. This study aimed to analyze by in silico, in vitro, and in vivo approaches to the feasibility of using the inhibitory protein extracted from mammals - Bovine Pancreatic Trypsin Inhibitor (BPTI) as a potential inhibitor of digestive trypsins from the pest Anticarsia gemmatalis and comparing the results with the host-plant inhibitor - Soybean Kunitz Trypsin Inhibitor (SKTI). BPTI and SKTI interacts with A. gemmatalis trypsin-like enzyme competitively, through hydrogen and hydrophobic bonds. A. gemmatalis larvae exposed to BPTI did not show two common adaptative mechanisms i.e., proteolytic degradation and overproduction of proteases, presenting highly reduced trypsin-like activity. On the other hand, SKTI-fed larvae did not show reduced trypsin-like activity, presenting overproduction of proteases and SKTI digestion. In addition, the larval survival was reduced by BPTI similarly to SKTI, and additionally caused a decrease in pupal weight. The non-plant protease inhibitor BPTI presents intriguing element to compose biopesticide formulations to help decrease the use of conventional refractory pesticides into integrated pest management programs.

Induced Resistance Combined with RNA Interference Attenuates the Counteradaptation of the Western Flower Thrips

The western flower thrips, Frankliniella occidentalis Pergande, is an invasive pest that damages agricultural and horticultural crops. The induction of plant defenses and RNA interference (RNAi) technology are potent pest control strategies. This study investigated whether the anti-adaptive ability of F. occidentalis to jasmonic acid (JA)- and methyl jasmonate (MeJA)-induced defenses in kidney bean plants was attenuated after glutathione S-transferase (GST) gene knockdown. The expression of four GSTs in thrips fed JA- and MeJA-induced leaves was analyzed, and FoGSTd1 and FoGSTs1 were upregulated. Exogenous JA- and MeJA-induced defenses led to increases in defensive secondary metabolites (tannins, alkaloids, total phenols, flavonoids, and lignin) in leaves. Metabolome analysis indicated that the JA-induced treatment of leaves led to significant upregulation of defensive metabolites. The activity of GSTs increased in second-instar thrips larvae fed JA- and MeJA-induced leaves. Co-silencing with RNAi simultaneously knocked down FoGSTd1 and FoGSTs1 transcripts and GST activity, and the area damaged by second-instar larvae feeding on JA- and MeJA-induced leaves decreased by 62.22% and 55.24%, respectively. The pupation rate of second-instar larvae also decreased by 39.68% and 39.89%, respectively. Thus, RNAi downregulation of FoGSTd1 and FoGSTs1 reduced the anti-adaptive ability of F. occidentalis to JA- or MeJA-induced defenses in kidney bean plants.

Source dependent variation in phenolics, antioxidant and antimicrobial activity of Paeonia emodi in west Himalaya, India

Paeonia emodi is one of the ethno therapeutically important Himalayan plants used to cure various diseases. However, a systematic investigation of the effect of altitude on phytochemical, antioxidant, and antimicrobial activity has not been reported so far. The present study assessed the variation in the bioactive compounds, antioxidant and antimicrobial activity of the leaf, and rhizome of P. emodi collected from different altitudes. Phytochemicals such as phenols, flavonoids, flavanol, tannins, emodin, and paeoniflorin were found in all the sampled populations, but the quantity varied significantly across the altitude. In leaf, phenolics, flavonoids, and tannins content positively correlated with altitude (p < 0.01), but flavanol did not show any connection. Similarly, in the rhizome, positive relation with altitude (p < 0.01) was observed in phenol, flavonoids, and paeoniflorin. Antioxidant activity measured by 1, 1-diphenyl- 2 picrylhydrazyl (DPPH) and nitric oxide assays showed a positive correlation (p < 0.05) with altitude. 2, 2-azinobis (3-ethylbenzothiazoline-6-sulphonic acid), ferric reducing antioxidant power, and hydroxyl ion assays did not show any relation with altitude. Antimicrobial activity was higher in the case of rhizome for the minimum inhibitory concentration and positively correlated with phenolics, flavonoids, and flavanol (p < 0.05). The present study further revealed that the secondary metabolites in the leaf and rhizome extracts of P. emodi are an excellent source of antioxidant and antimicrobial activity, thus validating the species' therapeutic potential.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01242-z.

Family dinner: Transcriptional plasticity of five Noctuidae (Lepidoptera) feeding on three host plant species

Polyphagous insects often show specialization in feeding on different host plants in terms of survival and growth and, therefore, can be considered minor or major pests of particular hosts. Whether polyphagous insects employ a common transcriptional response to cope with defenses from diverse host plants is under‐studied. We focused on patterns of transcriptional plasticity in polyphagous moths (Noctuidae), of which many species are notorious pests, in relation to herbivore performance on different host plants. We compared the transcriptional plasticity of five polyphagous moth species feeding and developing on three different host plant species. Using a comparative phylogenetic framework, we evaluated if successful herbivory, as measured by larval performance, is determined by a shared or lineage‐specific transcriptional response. The upregulated transcriptional activity, or gene expression pattern, of larvae feeding on the different host plants and artificial control diet was highly plastic and moth species‐specific. Specialization, defined as high herbivore success for specific host plants, was not generally linked to a lower number of induced genes. Moths that were more distantly related and showing high herbivore success for certain host plants showed shared expression of multiple homologous genes, indicating convergence. We further observed specific transcriptional responses within phylogenetic lineages. These expression patterns for specific host plant species are likely caused by shared evolutionary histories, for example, symplesiomorphic patterns, and could therefore not be associated with herbivore success alone. Multiple gene families, with roles in plant digestion and detoxification, were widely expressed in response to host plant feeding but again showed highly moth species‐specific. Consequently, high herbivore success for specific host plants is also driven by species‐specific transcriptional plasticity. Thus, potential pest moths display a complex and species‐specific transcriptional plasticity.

Competitive Plant-Mediated and Intraguild Predation Interactions of the Invasive Spodoptera frugiperda and Resident Stemborers Busseola fusca and Chilo partellus in Maize Cropping Systems in Kenya

Following its recent invasion of African countries, fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), now co-exists with resident stemborers such as Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Crambidae) causing severe damage to maize crops. Due to niche overlap, interspecific interactions occur among the three species, but the mechanisms and degree remain unclear. In this study, we assessed plant-mediated intraspecific and interspecific interactions, predation in laboratory and semi-field settings, and larval field occurrence of S. frugiperda and the two stemborer species. Larval feeding assays to evaluate competitive plant-mediated interactions demonstrated that initial S. frugiperda feeding negatively affected subsequent stemborer larval feeding and survival, suggesting induction of herbivore-induced mechanisms by S. frugiperda, which deters establishment and survival of competing species. Predation assays showed that, at different developmental larval stages, second−sixth instars of S. frugiperda preyed on larvae of both B. fusca and C. partellus. Predation rates of S. frugiperda on stemborers was significantly higher than cannibalism of S. frugiperda and its conspecifics (p < 0.001). Cannibalism of S. frugiperda in the presence of stemborers was significantly lower than in the presence of conspecifics (p = 0.04). Field surveys showed a significantly higher number of S. frugiperda larvae than stemborers across three altitudinally different agroecological zones (p < 0.001). In conclusion, this study showed that the invasive S. frugiperda exhibited a clear competitive advantage over resident stemborers within maize cropping systems in Kenya. Our findings reveal some of the possible mechanisms employed by S. frugiperda to outcompete resident stemborers and provide crucial information for developing pest management strategies for these lepidopteran pests.

Copper Chaperone for Superoxide Dismutase FoCCS1 in Frankliniella occidentalis May Be Associated with Feeding Adaptation after Host Shifting

Western flower thrips (Frankliniella occidentalis) pose a serious threat to the global vegetable and flower crop production. The regulatory mechanism for superoxide dismutase (SOD) in the feeding adaptation of F. occidentalis after host shifting remains unclear. In this study, the copper chaperone for SOD (CCS) and manganese SOD (MnSOD) genes in F. occidentalis were cloned, and their expression levels at different developmental stages was determined. The mRNA expression of FoCCS1 and FoMnSOD2 in F. occidentalis second-instar larvae and adult females of F₁, F₂, and F₃ generations was analyzed after shifting the thrips to kidney bean and broad bean plants, respectively. The F₂ and F₃ second-instar larvae and F₂ adult females showed significantly upregulated FoCCS1 mRNA expression after shifting to kidney bean plants. The F₁ second-instar larvae and F₂ adult females showed significantly upregulated FoCCS1 mRNA expression after shifting to broad bean plants. The RNA interference significantly downregulated the FoCCS1 mRNA expression levels and adult females showed significantly inhibited SOD activity after shifting to kidney bean and broad bean plants. F. occidentalis adult females subjected to RNA interference and released on kidney bean and broad bean leaves for rearing, respectively, significantly reduced the survival rate and fecundity. These findings suggest that FoCCS1 plays an active role in regulating the feeding adaptation ability of F. occidentalis after host shifting.

Hydrolysable tannins, physicochemical properties, and antioxidant property of wild-harvested Terminalia ferdinandiana (exell) fruit at different maturity stages

Terminalia ferdinandiana Exell., also known as Kakadu plum, is a wild-harvested native Australian fruit with limited information on how maturity is affecting the phytonutritional properties and bioactivities of the fruit. Thus, this study investigated changes in hydrolysable tannins, phenolic acids, sugar profile, standard physicochemical parameters, and antioxidant-scavenging capacity of wild-harvested Kakadu plum fruits at four different maturity stages, from immature to fully mature. Fruits harvested <25, 25-50, 50-75, and 75-100% degree of fullness were classified as highly immature (stage 1), immature (stage 2), semi-mature (stage 3), and fully mature (stage 4), respectively. Results showed that chebulagic acid, geraniin, chebulinic acid, castalagin, punicalagin, and gallic acid continuously decreased during fruit maturity, while elaeocarpusin, helioscopin B, corilagin, 3,4,6-tri-O-galloyl-S-glucose, and ellagic acid increased at the beginning of fruit growth (from stage 1 to 2), but decreased when the fruits reached their full maturity (stage 4). The levels of hydrolysable tannins and phenolic acids in fully mature fruits (stage 4) were significantly (p ≤ 0.05) lower than that in their immature counterparts (stages 1 and 2). Total phenolic content (TPC) and DPPH antioxidant radical-scavenging activity did not vary significantly between different maturity stages. Pearson's correlation coefficient test indicated that TPC and DPPH positively (p ≤ 0.05) correlate with most of the studied tannin compounds. Sugars (glucose, fructose, and sucrose), total soluble solid content, and titratable acidity increased during the fruit development. Furthermore, principal component analysis (PCA) revealed the difference between the immature and mature samples, based on their nutritional profile and bioactive compounds. The PCA results also suggested a considerable variability between the individual trees, highlighting the challenges of wild-harvest practice.

Development of a polyphagous leaf beetle on different host plant species and its detoxification of glucosinolates

Herbivores face a broad range of defences when feeding on plants. By mixing diets, polyphagous herbivores are assumed to benefit during their development by gaining a better nutritional balance and reducing the intake of toxic compounds from individual plant species. Nevertheless, they also show strategies to metabolically cope with plant defences. In this study, we investigated the development of the polyphagous tansy leaf beetle, Galeruca tanaceti (Coleoptera: Chrysomelidae), on mono diets consisting of one plant species [cabbage (Brassica rapa), Brassicaceae; lettuce (Lactuca sativa), or tansy (Tanacetum vulgare), Asteraceae] vs. two mixed diets, both containing tansy. Leaves of the three species were analysed for contents of water, carbon and nitrogen, the specific leaf area (SLA) and trichome density. Furthermore, we studied the insect metabolism of two glucosinolates, characteristic defences of Brassicaceae. Individuals reared on cabbage mono diet developed fastest and showed the highest survival, while the development was slowest for individuals kept on tansy mono diet. Cabbage had the lowest water content, while tansy had the highest water content, C/N ratio and trichome density and the lowest SLA. Lettuce showed the lowest C/N ratio, highest SLA and no trichomes. Analysis of insect samples with UHPLC-DAD-QTOF-MS/MS revealed that benzyl glucosinolate was metabolised to N-benzoylglycine, N-benzoylalanine and N-benzoylserine. MALDI-Orbitrap-MS imaging revealed the localisation of these metabolites in the larval hindgut region. 4-Hydroxybenzyl glucosinolate was metabolised to N-(4-hydroxybenzoyl)glycine. Our results highlight that G. tanaceti deals with toxic hydrolysis products of glucosinolates by conjugation with different amino acids, which may enable this species to develop well on cabbage. The high trichome density and/or specific plant chemistry may lower the accessibility and/or digestibility of tansy leaves, leading to a poorer beetle development on pure tansy diet or diet mixes containing tansy. Thus, diet mixing is not necessarily beneficial, if one of the plant species is strongly defended.

Plateau zokors (Eospalax baileyi) respond to secondary metabolites from the roots of Stellera chamaejasme by enhancing hepatic inflammatory factors and metabolic pathway genes

Herbivores rarely consume toxic plants. An increase in the proportion of toxic plant secondary metabolites (PSMs) in poisonous plants can promote detoxification and related metabolic capacity of animals. Poisonous plants with thick taproots like Stellera chamaejasme (SC) are important stored food for the plateau zokor (Eospalax baileyi) during the winter and promote the development of detoxification mechanisms in this animal. In this study, plateau zokors were administered gavages of 0.2, 1.05, and 2.10 ml/kg SC water extracts. Serum samples were collected from plateau zokors to measure the levels of transaminases and oxidative stress. Transcriptome analysis was conducted to evaluate the differential genes of multiple metabolic pathways to investigate the relationship between the physiological processes and metabolic adaptation capacity of these animals in response to SC. After SC administration, plateau zokors showed significant hepatic granular degeneration and inflammatory reactions in the liver and aspartate aminotransferase, alanine aminotransferase, and malondialdehyde levels increased in a dose-dependent manner. Further, differential expression was also found in the plateau zokor livers, with most enrichment in inflammation and detoxification metabolism pathways. The metabolic adaptation responses in P450 xenobiotic clearance, bile secretion, and pancreatic secretion (Gusb, Hmgcr, Gstm1, Gstp1, and Eobag004630005095) were verified by mRNA network analysis as key factors related to the mechanism. Plateau zokors respond to SC PSMs through changes in liver physiology, biochemistry, and genes in multiple metabolic pathways, validating our hypothesis that plateau zokors can metabolize PSMs when they ingest toxic plants.

Combined transcriptome and metabolome analysis of the resistance mechanism of quinoa seedlings to Spodoptera exigua

Quinoa has attracted considerable attention owing to its unique nutritional, economic, and medicinal values. The damage intensity of Spodoptera exigua at the seedling stage of quinoa fluctuates with the crop's biological cycle and the environmental changes throughout the growing season. In this study, we used independently selected quinoa seedling resistant and susceptible cultivars to investigate the difference between insect resistance and insect susceptibility of quinoa at the seedling stage. Samples were collected when Spodoptera exigua 45 days after planting the seedlings, and broad targeted metabolomics studies were conducted using liquid chromatography-mass spectrophotometry combined with transcriptomic co-analysis. The metabolomic and genomic analyses of the insect-resistant and insect-susceptible quinoa groups revealed a total of 159 differential metabolites and were functionally annotated to 2334 differential genes involved in 128 pathways using the Kyoto Encyclopedia of Genes and Genomes analysis. In total, 14 metabolites and 22 genes were identified as key factors for the differential accumulation of insect-resistant metabolites in quinoa seedlings. Among them, gene-LOC110694254, gene-LOC110682669, and gene-LOC110732988 were positively correlated with choline. The expression of gene-LOC110729518 and gene-LOC110723164, which were notably higher in the resistant cultivars than in the susceptible cultivars, and the accumulations of the corresponding metabolites were also significantly higher in insect-resistant cultivars. These results elucidate the regulatory mechanism between insect resistance genes and metabolite accumulation in quinoa seedlings, and can provide a basis for the breeding and identification of new insect-resistant quinoa cultivars as well as for screening potential regulatory metabolites of quinoa insect-resistant target genes.

Growth rate and life history shape plant resistance to herbivores

PREMISE

Plant defenses are shaped by many factors, including herbivory, lifespan, and mating system. Predictions about plant defense and resistance are often based on resource allocation trade-offs with plant growth and reproduction. Additionally, two types of plant resistance, constitutive and induced resistance, are predicted to be evolutionary alternatives or redundant strategies. Given the variety of plant trait combinations and non-mutually exclusive predictions, examining resistance strategies in related species with different combinations of growth and reproductive traits is important to tease apart roles of plant traits and evolutionary history on plant resistance.

METHODS

Phylogenetic comparative methods were used to examine the potentially interacting influences of life history (annual/perennial), mating system (self-compatible/self-incompatible), and species growth rates on constitutive resistance and inducibility (additional resistance following damage) across Physalis species (Solanaceae).

RESULTS

Resistance was evolutionarily labile, and there was no correlation between constitutive resistance and inducibility. Annual species with fast growth rates displayed higher constitutive resistance, but growth rate did not affect constitutive resistance in perennials. In contrast, inducibility was negatively associated with species growth rate regardless of life history or mating system.

CONCLUSIONS

The different effects of plant life history and growth rate on constitutive resistance and inducibility indicate that defensive evolution is unconstrained by a trade-off between resistance types. The interactions among plant life history, growth, and herbivore resistance show that plant defense is shaped not only by herbivore environment, but also by plant traits that reflect a plant's evolutionary history and local selective pressures.

Cell death and changes in primary metabolism: the onset of defence in Eucalyptus in the war against Leptocybe invasa

BACKGROUND

Here, we investigated changes in primary metabolism and cell death around oviposition sites in two hybrid clones of Eucalyptus with different degrees of resistance to Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae), as well as tolerance to water deficiency.

RESULTS

We showed that apices of the resistant clone with oviposition had a higher content of amino acids, organic acids and the compound putrescine compared with those of the susceptible clone with oviposition. By contrast, apices of the resistant clone with oviposition had lower sugar and pyruvate organic acid content than those of the susceptible clone with oviposition. Small areas of necrosis were induced around the oviposition sites in the stem apices of Eucalyptus 24 h after infestation. The resistant clone developed larger necrotic areas that showed progressive increases 24-72 h after infestation compared with the susceptible clone, in which cell death was significantly lower and no changes were observed in necrotic area over time. Thus, the programmed death of cells around the egg, modulated by several amino acids, is likely the first defence response of Eucalyptus against L. invasa.

CONCLUSION

Our results serve as the basis for the early identification of key metabolites produced in plants in defence against galling insects. © 2022 Society of Chemical Industry.

Leafminer attack accelerates the development of soil-dwelling conspecific pupae via plant-mediated changes in belowground volatiles

Herbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant-mediated interactions can occur between different herbivore species and different life developmental stages of the same herbivore. However, whether these interactions occur between leaf-feeding herbivores and their soil-dwelling pupae is unknown. We studied whether tomato (Solanum lycopersicum) leaf herbivory by the American serpentine leafminer Liriomyza trifolii affects the performance of conspecific pupae exposed to the soil headspace of the plant. To gain mechanistic insights, we performed insect bioassays with the jasmonate-deficient tomato mutant def-1 and its wild-type, along with phytohormones, gene expression and root volatiles analyses. Belowground volatiles accelerated leafminer metamorphosis when wild-type plants were attacked aboveground by conspecifics. The opposite pattern was observed for def-1 plants, in which aboveground herbivory slowed metamorphosis. Leafminer attack induced jasmonate and abscisic acid accumulation and modulated volatile production in tomato roots in a def-1-dependent manner. Our results demonstrate that aboveground herbivory triggers changes in root defence signalling and expression, which can directly or indirectly via changes in soil or microbial volatiles, alter pupal development time. This finding expands the repertoire of plant-herbivore interactions to herbivory-induced modulation of metamorphosis, with potential consequences for plant and herbivore community dynamics.

Volatiles and hormones mediated root-knot nematode induced wheat defense response to foliar herbivore aphid

Plant root-leaf communication signals are critical for plant defense. Numerous studies show that belowground organisms can alter systemically resistance traits in aboveground parts against herbivores. However, there are limited studies on root-knot nematode-aphid interaction. Moreover, the impact of nematode's initial density and infection time on plant defense is poorly understood. Here we aim to examine the induced defense responses by root-knot nematode Meloidogyne incognita against aboveground feeding aphid Sitobion avenae in wheat. Further, we investigated the influence of the nematode infection density as well as the length of infection in these interactions. We tested the direct and indirect defense responses triggered by M. incognita against S. avenae as well as how the responses affect the preference of Harmonia axyridis. Plant volatiles and hormones were determined to explore plant defense mechanisms that mediate aboveground-belowground defense. The photosynthetic rate was tested to examine plant tolerance strategy. We found that, both low and high densities M. incognita root infection at 7 days post inoculation (dpi) reduced the feeding of the aphid S. avenae. Behavioral assay showed that H. axyridis preferred plants co-damaged by both M. incognita and S. avenae at 7 dpi. M. incognita infection induced the changes of jasmonic acid, salicylic acid and volatile content, which mediated plant response to S. avenae. Furthermore, photosynthetic rate in wheat increased at 5 dpi under 300 M. incognita or 1000 M. incognita infection. These results suggest that plant roots induced multiple defense strategies against foliar herbivores as damages increased. Our study provides evidence of a complex dynamic response of wheat aboveground defense against aphids in response to belowground nematode damage on a temporal scale.

Species specific plant‐mediated effects between herbivores converge at high damage intensity

Plants are often exposed to multiple herbivores and densities of these attackers (or corresponding damage intensities) often fluctuate greatly in the field. Plant‐mediated interactions vary among herbivore species and with changing feeding intensity, but little is known about how herbivore identity and density interact to determine plant responses and herbivore fitness. Here, we investigated this question using Triadica sebifera (tallow) and two common and abundant specialist insect herbivores, Bikasha collaris (flea beetle) and Heterapoderopsis bicallosicollis (weevil). By manipulating densities of leaf‐feeding adults of these two herbivore species, we tested how variations in the intensity of leaf damage caused by flea beetle or weevil adults affected the performance of root‐feeding flea beetle larvae and evaluated the potential of induced tallow root traits to predict flea beetle larval performance. We found that weevil adults consistently decreased the survival of flea beetle larvae with increasing leaf damage intensities. In contrast, conspecific flea beetle adults increased their larval survival at low damage then decreased larval survival at high damage, resulting in a unimodal pattern. Chemical analyses showed that increasing leaf damage from weevil adults linearly decreased root carbohydrates and increased root tannin, whereas flea beetle adults had opposite effects as weevil adults at low damage and similar effects as them at high damage. Furthermore, across all feeding treatments, flea beetle larval survival correlated positively with concentrations of carbohydrates and negatively with concentration of tannin, suggesting that root primary and secondary metabolism might underlie the observed effects on flea beetle larvae. Our study demonstrates that herbivore identity and density interact to determine systemic plant responses and plant‐mediated effects on herbivores. In particular, effects are species‐specific at low densities, but converge at high densities. These findings emphasize the importance of considering herbivore identity and density simultaneously when investigating factors driving plant‐mediated interactions between herbivores, which advances our understanding of the structure and composition of herbivore communities and terrestrial food webs.

Analysis of the transcriptome of the needles and bark of Pinus radiata induced by bark stripping and methyl jasmonate

BACKGROUND

Plants are attacked by diverse insect and mammalian herbivores and respond with different physical and chemical defences. Transcriptional changes underlie these phenotypic changes. Simulated herbivory has been used to study the transcriptional and other early regulation events of these plant responses. In this study, constitutive and induced transcriptional responses to artificial bark stripping are compared in the needles and the bark of Pinus radiata to the responses from application of the plant stressor, methyl jasmonate. The time progression of the responses was assessed over a 4-week period.

RESULTS

Of the 6312 unique transcripts studied, 86.6% were differentially expressed between the needles and the bark prior to treatment. The most abundant constitutive transcripts were related to defence and photosynthesis and their expression did not differ between the needles and the bark. While no differential expression of transcripts were detected in the needles following bark stripping, in the bark this treatment caused an up-regulation and down-regulation of genes associated with primary and secondary metabolism. Methyl jasmonate treatment caused differential expression of transcripts in both the bark and the needles, with individual genes related to primary metabolism more responsive than those associated with secondary metabolism. The up-regulation of genes related to sugar break-down and the repression of genes related with photosynthesis, following both treatments was consistent with the strong down-regulation of sugars that has been observed in the same population. Relative to the control, the treatments caused a differential expression of genes involved in signalling, photosynthesis, carbohydrate and lipid metabolism as well as defence and water stress. However, non-overlapping transcripts were detected between the needles and the bark, between treatments and at different times of assessment. Methyl jasmonate induced more transcriptional responses in the bark than bark stripping, although the peak of expression following both treatments was detected 7 days post treatment application. The effects of bark stripping were localised, and no systemic changes were detected in the needles.

CONCLUSION

There are constitutive and induced differences in the needle and bark transcriptome of Pinus radiata. Some expression responses to bark stripping may differ from other biotic and abiotic stresses, which contributes to the understanding of plant molecular responses to diverse stresses. Whether the gene expression changes are heritable and how they differ between resistant and susceptible families identified in earlier studies needs further investigation.

Expanding the Menu: Are Polyphagy and Gene Family Expansions Linked across Lepidoptera?

Evolutionary expansions and contractions of gene families are often correlated with key innovations and/or ecological characteristics. In butterflies and moths (Lepidoptera), expansions of gene families involved in detoxification of plant specialized metabolites are hypothesized to facilitate a polyphagous feeding style. However, analyses supporting this hypothesis are mostly based on a limited number of lepidopteran species. We applied a phylogenomics approach, using 37 lepidopteran genomes, to analyze if gene family evolution (gene gain and loss) is associated with the evolution of polyphagy. Specifically, we compared gene counts and evolutionary gene gain and loss rates of gene families involved in adaptations with plant feeding. We correlated gene evolution to host plant family range (phylogenetic diversity) and specialized metabolite content of plant families (functional metabolite diversity). We found a higher rate for gene loss than gene gain in Lepidoptera, a potential consequence of genomic rearrangements and deletions after (potentially small-scale) duplication events. Gene family expansions and contractions varied across lepidopteran families, and were associated to host plant use and specialization levels. Within the family Noctuidae, a higher expansion rate for gene families involved in detoxification can be related to the large number of polyphagous species. However, gene family expansions are observed in both polyphagous and monophagous lepidopteran species and thus seem to be species-specific in the taxa sampled. Nevertheless, a significant positive correlation of gene counts of the carboxyl- and choline esterase and glutathione-S-transferase detoxification gene families with the level of polyphagy was identified across Lepidoptera.

Cooperative herbivory between two important pests of rice

Normally, when different species of herbivorous arthropods feed on the same plant this leads to fitness-reducing competition. We found this to be different for two of Asia's most destructive rice pests, the brown planthopper and the rice striped stem borer. Both insects directly and indirectly benefit from jointly attacking the same host plant. Double infestation improved host plant quality, particularly for the stemborer because the planthopper fully suppresses caterpillar-induced production of proteinase inhibitors. It also reduced the risk of egg parasitism, due to diminished parasitoid attraction. Females of both pests have adapted their oviposition behaviour accordingly. Their strong preference for plants infested by the other species even overrides their avoidance of plants already attacked by conspecifics. This cooperation between herbivores is telling of adaptations resulting from the evolution of plant-insect interactions, and points out mechanistic vulnerabilities that can be targeted to control these major pests.

Seasonal Variation in Host Plant Chemistry Drives Sequestration in a Specialist Caterpillar

Sequestration of plant secondary metabolites by herbivores can vary across both host plant phenology and herbivore ontogeny, but few studies have explored how they concurrently change in the field. We explored variation in iridoid glycoside concentration and composition in white turtlehead, Chelone glabra, as well as sequestration of iridoid glycosides by its specialist herbivore, the Baltimore checkerspot, Euphydryas phaeton, across the development of both herbivore and host plant. In 2012 we sampled plants to describe seasonal variation in the concentrations of two iridoid glycosides, aucubin and catalpol. In 2017, we sampled both host plants and caterpillars over an entire growing season and explored the relationship between plant chemistry and herbivore sequestration. We also compared iridoid glycoside concentrations of plants with and without herbivory to gain insight into whether levels of secondary compounds were impacted by herbivory. We found that total plant iridoid glycosides varied across the season and that total sequestered iridoid glycosides in caterpillars closely mirrored concentration patterns in plants. However, the magnitude of sequestration by caterpillars ranged from 2 to 20 times the concentrations in host plants, with different proportions of aucubin and catalpol. In addition, plants with herbivory had lower iridoid glycoside concentrations than plants without herbivory, although this difference changed over time. These results suggest that while variation in host plant secondary metabolites may be a dominant factor driving sequestration, other ecological factors may mitigate the relationship between host plant chemistry and herbivore sequestration.