(+)-Catechin from Prunus padus disrupts detoxification pathways and provides field-level control of the bird cherry-oat aphid, Rhopalosiphum padi.

Pathogen and pest effectors play a crucial role in manipulating plant biological processes, facilitating infection and infestation. While pathogens and pests secrete repertoires of effectors into host plants, most effector function studies focus on characterising individual proteins. Our previous work identified a genetically linked and co-regulated gene pair in the aphid pest Myzus persicae encoding effectors Mp1 and Mp58. Here, we explored the functional link between these two effectors. We revealed that effectors Mp1 and Mp58 interact in planta and in vitro and form an oligomeric complex. The putative orthologs of the Mp1-Mp58 pair in the aphid species Rhopalosiphum padi, Rp1 and Rp58 also interact, but members of the pair cannot interact across aphid species, suggesting that effector pairs have co-evolved within each aphid species but diversified across species. Both Mp1 and Mp58 associate with the host Vacuolar Protein Sorting associated Protein 52 (VPS52) to form an Mp1-Mp58-VPS52 complex which localises at vesicle-like structures. Our findings point to effector complex formation in plant-insect interactions and highlight a further layer of complexity in the molecular dialogue between insects and their host plants. Our work highlights the importance of considering the context in which effectors may function within a larger effector repertoire.

Rhopalosiphum padi (L.) is a major vector of barley yellow dwarf virus (BYDV), one of the most economically damaging viral diseases of cereals, including wheat. Although host resistance to BYDV or to aphids individually has been exploited, less is known about how aphid resistance performs against viruliferous vectors. We recently identified a winter genotype (G1) exhibiting strong aphid resistance through antixenosis and antibiosis. Here, we test whether this resistance remains effective against BYDV-vectoring aphids and how it compares with BYDV resistance. We evaluated G1 alongside four wheat cultivars with contrasting aphid and BYDV resistance traits, including the BYDV-resistant cultivar RGT Wolverine and the fully susceptible RGT Illustrious. Seedling settlement assays showed that antixenosis in G1 remained effective against R. padi carrying BYDV-PAV. Electrical penetration graph recordings revealed restricted phloem access and reduced salivation of viruliferous aphids on G1, consistent with lower virus transmission efficiency. Quantitative reverse transcription polymerase chain reaction showed a threefold reduction in BYDV gene expression in inoculated leaves of G1 compared with RGT Wolverine and RGT Illustrious. By contrast, RGT Wolverine exhibited high initial transmission but reduced systemic infection, consistent with resistance acting on suppression of viral replication and/or movement. Aphid rearing host genotype altered subsequent aphid host-selection behaviour, indicating vector conditioning with consequences for virus spread. Aphid resistance in G1 significantly reduced BYDV transmission, whereas Bdv2-mediated resistance in RGT Wolverine limited systemic infection. These complementary resistance mechanisms highlight the value of combining aphid- and virus-targeted traits to improve durable BYDV management in wheat. © 2026 Society of Chemical Industry.

Aphids are one of the most damaging piercing-sucking pests in rice production, whose population outbreaks cause crop losses amounting to hundreds of millions of dollars annually worldwide. To address this challenge, it is highly imperative to develop aphid-resistant rice varieties through techniques such as genetic modification. In this study, we successfully targeted the (E)-β-farnesene synthase (EβFS) to the chloroplast using the promoter of the rice Rubisco small subunit gene (rbcS) and its chloroplast transit peptide (ctp), which significantly enhanced the production of (E)-β-farnesene (EβF) in transgenic rice. At the seedling stage, the EβFS protein content was 17.6-fold higher in transgenic rice compared with that in the rice previously generated using the cauliflower mosaic virus 35S promoter (35S::EβFS). At the tillering stage, the EβF release rate reached 12.7 μg per plant per day in the transgenic rice. Olfactory behavioral assays demonstrated that the transgenic rice line generated in this study had significantly enhanced ability to repel bird cherry-oat aphids (Rhopalosiphum padi) ('Push' effect) and attract its natural enemy multicolored Asian lady beetles (Harmonia axyridis) ('Pull' effect) compared with the 35S::EβFS lines. In addition, the rbcS promoter can achieve specific expression of the EβFS gene in photosynthetic organs, avoiding unnecessary consumption of energy and resources associated with constitutive expression. This Push-Pull strategy could protect rice plants from aphid infestation by controlling the aphid populations, providing an ecologically friendly and sustainable approach for integrated pest management in rice fields. © 2025 Society of Chemical Industry.

Native bacterial endosymbionts in aphids have been studied for many years but it is only recently that transinfections across species are being investigated from an applied perspective. Here we consider the impact of a Rickettsiella viridis transinfection originally from the pea aphid Acyrthosiphon pisum, in an important pest of cereals, Rhopalosiphum padi, that causes feeding damage and transmits barley yellow dwarf virus (BYDV). Our main aims were to quantify the fitness and dispersal consequences of the transinfection, assess its transmission dynamics, and determine whether Rickettsiella influences BYDV acquisition or transmission. The transinfected strain had fitness costs in its new aphid host, with an intrinsic rate of increase (rm) value around 20% lower, and showed horizontal transmission. Rickettsiella did not transmit vertically with complete fidelity, although it persisted in population cages for at least 11 weeks. Although Rickettsiella did not affect transmission of BYDV, it reduced the production of alates by 10% or more depending on aphid density. Aphids carrying Rickettsiella showed a slower rate of movement to adjacent plants compared with those without Rickettsiella. The body colour of aphids with Rickettsiella was also darker. This Rickettsiella transinfection imposes deleterious host effects, while retaining the capacity to persist in populations through horizontal transmission. Although it does not influence BYDV transmission, the reduced alate formation and slower movement suggest potential impacts on pest spread and population structure. These findings advance our understanding of symbiont-host interactions and highlight the potential for endosymbiont manipulations to influence aphid ecology and management. © 2026 Society of Chemical Industry.

Bird cherry aphid Rhopalosiphum padi (L.) is a common pest of grain crops. To control its harmfulness, there is a great necessity in a reliable method to estimate aphid abundance and spread in the field and to fulfil screening of resistant accessions for feeding in vegetation. The flight behavior patterns or selection of hidden sites by wingless insects within plants, as well as the wing emergence of offspring on cereal grasses, have been poorly studied, although they are important for aphid reproduction and harmfulness. The purpose of the current study was to optimize methodological approaches to estimating R. padi abundance due to its specific topical distribution and wing emergence. The field study and model trials have identified the features of R. padi’s topical distribution that had been overlooked. There has been shown that aphid can remain below the soil surface when feeding on wheat (the variety ‘Leningradskaya 6’) and 10 species of cereal grasses during the period of ‘tillering-early stem formation’. Their maximum abundance was 18.7 % on wheat (field) and 25.8 % on multiflora ryegrass (Tarquin) (model trials). There has been found that one of the causes of such migrations may be tactile stimuli, as a result of which the “hidden” number of insects in model trials (touching with a brush) has increased on average from 6.0 to 11.5 %. This feature should be taken into account when assessing R. padi population density. The current work has characterized the wing dimorphism of aphids and the role of both summer morphotypes in plant damage. The use of winged females to screen for plant suitability for aphid feeding poses challenges because of their flight activity. There has been found that female wing manipulations, which simulate the “crowding effect” and increase wing emergence of offspring through prenatal transgenerational transmission of relevant signals, distort the estimation results and cannot be used.

Agriculture intensification, massively relying on pesticides, led to the widespread contamination of noncrop terrestrial ecosystems. Soil contamination with pesticide residues widely occurs but its cryptic effects on terrestrial biotic interactions remain unclear, especially at the metabolic scale. We studied the effects of an environmental dose of the herbicide isoproturon on an isoproturon-degrading Sphingomonas soil bacteria - Lolium perenne (Poaceae) and Rhopalosiphum padi (Hemiptera: aphididae) system - in the laboratory. This system is typical of contaminated peri-agricultural ecosystems, such as vegetated buffer strips. We found that isoproturon and its main degradation product transferred from the substrate to aphids, accumulating in plant shoots. No macroscopic effects of the herbicide were observed, but primary metabolites varied in both plants and herbivores. Inoculation of isoproturon-degrading bacteria reduced isoproturon levels in the substrate and suppressed most metabolic variations. Moreover, inoculation of the non-degrading bacterial strain impacted plant metabolism, potentially through mutualistic interaction, underlining the close link between soil microbiota and aboveground organisms. This study shows that isoproturon residues can transfer in a typical grassland trophic system, altering the metabolism of each biological level. It emphasizes the need to consider above- and belowground interactions when assessing seminatural ecosystems' responses to chronic contamination.

Mutualistic symbioses between plants and fungi are widespread in nature and increasingly being adopted in agroecosystems to enhance economic and environmental sustainability. In temperate forage grasses, associations with Epichloë endophytic fungi can confer resistance to herbivores, particularly aphids. While their impact on aphid preference and performance are well documented, the underlying behavioral mechanisms remain poorly understood. We investigated interactions between two tall fescue cultivars (INIA Aurora and INIA Fortuna), the AR584 strain of Epichloë coenophiala , and the bird cherry‐oat aphid Rhopalosiphum padi , focusing on feeding behaviour using the electrical penetration graph (EPG) technique. Plants (both adult and seedling stages) with and without the endophyte were tested in both choice and no‐choice experiments under greenhouse conditions. Aphid populations grew ~10% faster on endophyte‐free plants, with significantly higher numbers of apterae and nymphs after three weeks. In choice tests, aphids preferred endophyte‐free plants, and aphid‐free plants showed greater biomass. Daily fecundity was consistently lower on endophyte‐infected plants, regardless of cultivar, and aphids performed best on wheat controls. EPG analysis revealed that on endophyte‐infected plants, aphids exhibited shorter phloem ingestion phases, delayed time to sustained ingestion, and increased probing activity, particularly in mesophyll. In seedlings, similar feeding disruptions were observed, including increased xylem ingestion and reduced duration of sustained phloem feeding. These findings demonstrate that Epichloë endophytes disrupt aphid feeding behavior, particularly access to phloem sap, leading to reduced performance and host preference. This supports their potential role in integrated pest management strategies via enhancement of plant resistance, offering insights into the functional mechanisms behind this symbiosis.

Chemosensory proteins (CSPs) are small soluble proteins that play various roles in insects. The non-sexual parthenogenetic females (virginoparae) of Rhopalosiphum padi can transition to sexual reproduction and produce sexual females (oviparae) when exposed to short photoperiods and low temperatures. To date, research on the distinct roles of chemosensory proteins in sexual versus parthenogenetic female aphids remains scarce. In this study, we investigated the roles of RpCSP8 in R. padi. Among the eight RpCSPs, RpCSP8 exhibited a 3.81 fold higher expression in the oviparae compared to virginoparae. Across developmental stages and tissues, RpCSP8 showed the highest expression in the fourth-instar nymphs and adults, as well as in the salivary glands of oviparae. In contrast, it exhibited the highest expression in adults and the antennae of virginoparae. In oviparae, knockdown of RpCSP8 significantly impaired reproductive performance: fecundity decreased by over 80%, and lifespan was reduced by more than 50%. RpVg (vitellogenin) expression declined by 37.1%, although no significant differences in egg morphology were detected. Electrical penetration graph (EPG) recordings revealed that RpCSP8 knockdown in oviparae significantly reduced phloem ingestion duration, indicating impaired feeding behavior. In virginoparae, knockdown of RpCSP8 showed no significant changes in fecundity, lifespan, or feeding behavior. These results demonstrate different roles for RpCSP8 in regulating both reproductive output and host plant utilization in the oviparae and virginoparae of R. padi. This study reveals the non-chemosensory functions of insect CSP and provides new insights into the adaptive mechanisms underlying reproductive mode transitions and host switching in R. padi.

Long non-coding RNAs (lncRNAs) are non-coding transcripts that regulate various biological processes in many species, including insects. Some lncRNAs have been found to be associated with insecticide resistance. In this study, 4177 lncRNAs between the susceptive strain (RP-S) and the imidacloprid-resistant strain (RP-R) in Rhopalosiphum padi by transcriptome sequencing were recognized, including 2401 intergenic lncRNAs, 970 intron lncRNAs, and 806 antisense lncRNAs. Two hundred fifty-eight differentially expressed lncRNAs were observed, including 77 lncRNA transcripts that were upregulated, while 181 lncRNA transcripts were downregulated in RP-R compared to that in RP-S targeting 628 differentially expressed mRNAs. They could be involved in imidacloprid resistance by modulating the expression of 11 P450s, 2 CCEs, 6 UGTs, and 14 ABC transporters. Furthermore, quantitative PCR (qPCR), RNA interference (RNAi), and imidacloprid bioassay analyses demonstrated that overexpressed lnc8676, lnc36817, and lnc48853 were involved in imidacloprid resistance. This study provided comprehensive information on the lncRNAs profile and provided evidence that lncRNAs play a key role in conferring insecticide resistance to R. padi and have significant potential to be used as targets for pest control strategies.

Wheat (Triticum aestivum L.) is an important grain and staple food crop, which plays an important role in the economy of Pakistan. Wheat crop suffers a lot of yield loss due to insect pests attack, which affects plant life and grain yield. Cultivation of pest resistant/tolerant varieties is the main method to combat these losses. Among the insect pests the aphid Rhopalosiphum padi is a main destructive pests of wheat crop which cause a considerable damage to wheat production in Sindh Pakistan. The current study focus on different resistant wheat varieties against population of aphid R. padi against aphid under field condition. Results of currant study showed significantly maximum population of R. padi (13.54±2.26/tiller) was recorded on Kiran, followed by TJ-83 11.35±2.12/tiller, Sattar 7.23±1.64/tiller, Mehran 5.08±1.13/tiller, TH-83 4.33±0.98/tiller, NIA Sunder 2.25±0.52/tiller, NIA Amber 2.72±0.60/tiller, Khirman 3.17±0.67/tiller, NIA Sarang 3.61±0.77/tiller, while manimum population was found on TD-1 (1.63±0.40/tiller) genotype respectively. The results indicated that highest yield of wheat genotype was recorded from TD-1 (6249.5 kg) followed by NIA Sunder (4562.1 kg), TH-23 (4343.1 kg), Mehran (4311.5 kg), Khirman (4193.2 kg), NIA Amber (3466.1 kg), NIA Sarang (3306.8 kg), Sattar (2826.2 kg), TJ-83 (2400.5 kg) whereas the Kiran genotypes found lowest (2293.1 kg) yield respectively.

Durum wheat (Triticum durum) is a staple crop in the Mediterranean region, where it faces serious threats from arthropod pests that can significantly reduce yields. This study aimed to assess the diversity and seasonal dynamics of insect pest communities associated with durum wheat under contrasting climatic conditions in northern Algeria. A total of 18 and 20 species were recorded at the semi-arid and sub-humid sites, represented by Bouira and Algiers respectively, with seven dominant and common species identified at both sites: Aeolothrips fasciatus, Limothrips cerealium, Haplothrips tritici, Melanthrips pallidior (Thysanoptera), Hydrellia griseola, Liriomyza trifolii (Diptera), and Rhopalosiphum padi (Hemiptera). Insect populations were present throughout the wheat growth cycle, with abundance peaks occurring in February at Algiers and in May at Bouira. A general decrease in insect numbers was observed with rising temperatures, although this trend varied among species. The findings enhance current understanding of pest assemblages in North African cereal systems and support the development of regionally adapted and ecologically sound monitoring and pest management strategies.

Climate change, through rising temperatures, greater variability, and more frequent extremes, is reshaping insect phenology and thermal niches, with profound effects for pest outbreaks. Predicting these impacts requires a clear understanding of species and communities' responses across geographic gradients. We assessed thermal tolerance (CTmax, CTmin, CCRT) of three cereal aphid species Sitobion avenae , Rhopalosiphum padi , Metopolophium dirhodum from 30 populations along a 1200 km longitudinal gradient in Europe, comparing autumn and spring collections. We measured guild‐level functional diversity to assess thermal trait patterns along the longitudinal gradient. We tested whether 1) eastern populations experiencing greater seasonality and harsher winters exhibited broader thermal ranges, 2) autumn aphids were more cold‐tolerant and less heat‐tolerant than spring aphids, and 3) stronger seasonality facilitated thermal trait convergence within the guild. Across the longitudinal gradient, autumn populations in eastern Europe exhibited broader thermal ranges, supporting the climatic variability hypothesis (CVH). In contrast, spring populations displayed a counter‐gradient pattern, with stronger cold tolerance in the milder western winters, likely reflecting differences in overwintering strategies (active adults in the west versus diapausing eggs in the east). Additionally, autumn aphids were less heat‐tolerant than spring individuals. Eastern communities exhibited trait convergence driven by large intraspecific variation, whereas western communities showed interspecific divergence, indicating differential environmental filtering. Increasing climate variability may drive thermal traits homogenization (negative standardized effect size of functional diversity for all traits) in ectotherm communities. Climate change may intensify season‐dependent physiological changes, shift eastward the geographic range of aphids overwintering as active adults, and homogenize thermal niches, potentially altering pest dynamics and diminishing the effectiveness of integrated pest management strategies. Our study underscores the importance of integrating seasonal dynamics and intraspecific trait variations when predicting climate change responses, highlighting how changes in temperature variability – not just warming – may reshape ectotherm communities during the growing season.

Grasses have primarily coevolved with large grazing herbivores, a relationship that has strongly shaped their defensive architecture. This evolutionary history has led to the development of traits such as basal meristems and prolific tillering, enabling rapid regrowth following grazing. Consequently, grasses typically lack a diverse arsenal of chemical defences and instead rely on alternative strategies, including rapid tissue turnover, physical barriers, and symbiotic associations with microorganisms to deter insect herbivores. Microbial symbionts may provide chemical protection, while structural defences, such as silicon accumulation, play a key role. Silicon serves as a major structural defence against both biotic and abiotic stress, comprising up to 10% of grass dry mass. Many temperate grasses associate with mutualistic fungi, such as Epichloë endophytes and arbuscular mycorrhizal fungi, and these symbiotic plants can exhibit altered host chemistry, subsequently influencing herbivore interactions. However, few studies have investigated how silicon-based physical defences interact with these fungal symbionts and their chemical defence mechanisms. This research addressed this knowledge gap by examining how silicon, Epichloë, and arbuscular mycorrhizal fungi interacted to affect plant resistance to insect herbivores. Two forage grasses (Festuca arundinacea and Lolium perenne) with contrasting leaf dynamics, were studied under factorial combinations of silicon supplementation, fungal inoculation (five novel grass-Epichloë associations [tall fescue: AR584 or common-toxic; perennial ryegrass: AR37, AR1, or common-toxic] or as Epichloë-free controls], and one arbuscular mycorrhizal fungal strain of Rhizophagus irregularis), and herbivore pressure from Helicoverpa armigera (a moth) and Rhopalosiphum padi (an aphid). Experiments showed that all Epichloë strains increased silicon concentrations in tall fescue on average to 31%. Of the five Epichloë strains in perennial ryegrass only strain AR37 had any effect increasing silicon concentrations. Silicon also enhanced Epichloë colonization (fungal mass) in tall fescue, but not in perennial ryegrass. In soil systems, silicon reduced the growth of H. armigera more effectively than any of the Epichloë strains, though both silicon and Epichloë contributed to plant defence in a compatible, non-antagonistic manner. In perennial ryegrass, silicon influenced Epichloë-derived alkaloid production, specifically epoxyjanthitrems. Scanning electron microscopy revealed that silicon and Epichloë could compatibly enhance surface defences and reduce insect feeding efficiency, while also compromising herbivore immunity. In a final experiment using only AR584 in tall grass fescue, tripartite interactions involving arbuscular mycorrhizal fungi, Epichloë, and silicon were explored under aphid attack. While endophytes suppressed aphid performance, arbuscular mycorrhizal fungi counteracted these effects, potentially through reduced alkaloid levels and increased foliar nitrogen. Silicon increased uptake in all symbiotic treatments but did not affect aphid performance. Overall, this research provided novel insights into the complex and context-dependent nature of grass defence systems. Silicon offered stronger protection against folivores, while endophyte-derived alkaloids were more effective against aphids. Interactions between fungal symbionts and silicon varied by plant species, fungal genotype, and herbivore type. These findings underscore the potential of harnessing natural plant–microbe–silicon interactions to enhance grass resilience against a range of biotic stressors, offering valuable insights for the development of more sustainable forage systems.

The presence of Epichloë-infected grasses in South America was inadvertently reported in 1908 when two veterinaries attributed the cause of the poisoning in cattle and livestock to the consumption of Festuca plants infected with a fungus that they wrongly identified and named Endoconidium tembladerae (today Epichloë tembladerae). It was only at the end of the 20th century that systematic studies of endophytes in Argentinian native grasses began, and the host list of new and already known Epichloë endophytes is continually expanding. The team at UBA-FCEyN and CONICET-UBA have, and continue, to work on three central projects: Toxic and mammalian safe genotypes of Epichloë associated with native fescues. Festuca fiebrigii and F. argentina associate with Epichloë tembladerae and in populations of F. argentina endophyte incidence is higher than 90%. These endophyte-grass associations are infamous for their toxicity to livestock with preliminary analyses suggesting that mammalian toxicity is due to the production of the alkaloids terpendole C and I. However, extensive surveys in F. fiebrigii populations have now revealed that this grass species also associates with several non-toxic genotypes of E. tembladerae, and these endophytes may contribute to the development of novel forages for Argentina. Recently, we have also detected a new toxic endophyte genetically related to E. aotearoae but more difficult to culture. E. aotearoae is a symbiont of Echinopogon ovatus, a grass endemic to New Zealand. Endophytes in wild forage grasses. Bromus auleticus, an important forage grass, is associated with at least three peramine producing Epichloë species, E. pampeana, E. tembladerae and E. platensis. Only the N-formylloline producing E. pampeana is harmful to aphids (Rhopalosiphum padi) while none of these endophytes have effects on the feeding preference of crickets (Gryllus assimilis). However, B. auleticus plants infected with E. platensis are more tolerant to root feeding scarab beetle larvae (Philochloenia bonariensis). Current research aims to further understand the complexity of insect resistance within these grass-endophyte associations. Epichloë endophytes also modulate host physiology in B. auleticus. Germination of endophyte-infected (E+) seeds was prevented under low water activity and salinity and E+ plants, exposed to water deficit, suffered less cellular damage, maintained higher values of stomatal conductance and net photosynthesis than (endophyte-free) E- plants. The Epichloë endophytes also modulate the community of non-systemic foliar endophytes and the community structure of cultivable dark septate endophytes in roots of B. auleticus differed between E+ and E- plants with higher proportions of pathogenic fungi in the E- plants. Inoculation of Argentinean endophytes in commercial forage grasses. The wide host range, genetic and chemical diversity, and the advantageous traits conferred upon their original host grasses led to research developing novel grass-endophyte associations. Attempts were made to infect commercial forage grasses and barley (Hordeum vulgare) with E. tembladerae, E. cabralii and E. pampeana. Only Lolium multiflorum inoculated with E. tembladerae formed a stable association. This association remained stable for five generations and these plants did not behave differently from those associated with their original endophyte, E. occultans. Summarizing, more research is needed to understand the complexity and the potential of endophyte-grass associations in South America.

Epichloë endophytes form systemic, vertically transmitted symbioses with cool-season grasses, providing chemical defence against herbivores through alkaloid production. While often described as a ‘defensive mutualism’, the fitness costs of this relationship for the host plant, particularly across generations, remain poorly understood. This study investigated whether repeated defoliation of Festuca pratensis (meadow fescue) mother plants alters seed production, seed viability, and the endophyte-conferred resistance of progeny plants. A common-garden experiment was established using both endophyte-symbiotic (E+) and endophyte-free (E–) plants. Over one growing season, half of the plants were subjected to severe, repeated defoliation to simulate grazing stress. Plant biomass, inflorescence number, seed biomass, chlorophyll activity, and alkaloid concentrations in leaves and seeds were quantified. Seed viability and germination rates were tested, followed by a greenhouse experiment where progeny were challenged with the aphid Rhopalosiphum padi to assess resistance conferred by maternally induced alkaloids. Results revealed a strong resource allocation trade-off. Defoliation reduced leaf alkaloid concentrations in E+ plants but increased alkaloid investment into seeds. This shift enhanced seed protection and provided seedlings with elevated alkaloid levels during the first six weeks of growth. Consequently, progeny of defoliated E+ plants exhibited reduced aphid performance compared with progeny of non-defoliated E+ plants, confirming a transgenerational defensive effect. However, these benefits came at a reproductive cost: seeds from defoliated E+ plants had significantly lower germination rates than seeds from E+ non-defoliated or E– plants. Germination was negatively correlated with seed alkaloid concentrations, suggesting that endophyte-driven defence investment compromised reproductive success. These findings highlight a context-dependent nature of the grass–endophyte relationship. Under intense foliar stress, the endophyte prioritizes transgenerational defence, allocating resources toward alkaloid-enriched seeds at the expense of seed viability. While this strategy enhances early-stage herbivore resistance in progeny, it reduces the number of viable offspring, suggesting a fitness trade-off between defence and reproduction. From an evolutionary perspective, this dual outcome may help explain the observed variability of endophyte frequencies in natural grass populations. In environments with high herbivory pressure, enhanced seed protection could outweigh reduced germination, whereas under low herbivory, the cost to reproductive output may favour endophyte-free grasses. Overall, the study demonstrates that Epichloë-conferred defensive mutualism does not fully bypass the growth–defence trade-off but instead redistributes it across generations, balancing survival advantages against reproductive costs.

A comprehensive survey of Epichloë fungal endophytes forming symbioses with the wild C3 forage grass Bromus auleticus across a transitional climate–soil zone in Uruguay was conducted. Among 83 accessions, we detected 70% were infected with Epichloë. Using PCR with 29 genetic markers targeting tefA, mating type and alkaloid biosynthesis genes we identified nine distinct Epichloë genotypes that varied in potential alkaloid production. Of these nine genotypes, 1, 2 and 3 were most commonly observed. All genotypes contained the genes required for the synthesis of pyrrolopyrazines (e.g., peramine, a known insect-feeding deterrent). Two genotypes (designated 1 and 7) contained genes required for the synthesis of pyrrolizidines (e.g. loline alkaloids, known for their broad spectrum insecticidal and insect-deterrent activity), but only genotype 1 was predicted to produce N-formylloline, a compound with strong insecticidal properties. Seven genotypes (2, 3, 4, 5, 6, 8 and 9) contained genes involved in indole diterpene (IDT) synthesis, however, only five genotypes (2, 3, 4, 5, and 6) were predicted to produce early pathway IDTs such as paspaline or terpendoles. Genotypes 8 and 9 lacked essential early pathway genes were not predicted to produce IDTs. Genotypes 3 and 7 contained EAS genes required for ergot alkaloid synthesis; however, these genotypes were only predicted to produce chanoclavine, as genes required for downstream ergovaline synthesis were absent. None of the Epichloë endophytes from this survey contained genes required for the synthesis of the mammalian toxins ergovaline or lolitrem B. As genotypes 1, 2, and 3 were the most prevalent in the collection, six plant accessions, two from each of these genotypes, were selected to evaluate the protective effects of their different Epichloë genotypes against the aphid Rhopalosiphum padi, a generalist insect, in laboratory-controlled bioassays. Notably, only the plant accessions associated with genotype 1, predicted to produce N-formylloline, significantly suppressed R. padi. Endophyte presence and distribution were strongly influenced by environmental factors, particularly water availability, soil organic matter, and temperature extremes. Additionally, plants associated with endophyte genotypes 1, 2 and 3 were grown in two contrasting environments, displayed genotype-specific effects on host performance emerged under different soil fertility conditions. These findings highlight the ecological and agronomic potential of Epichloë endophytes that would lack mammalian toxicity and could provide a foundation for developing sustainable forages with enhanced insect resistance and environmental resilience without compromising livestock health.

Unveiling the efficacy of a novel strain of Beauveria brongniartii to manage Sitobion miscanthi (Takahashi) and Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae) in China

Changes in atmospheric CO2 are known to influence plant physiology, subsequently affecting the nature of their interactions with their biotic environment. Barley yellow dwarf virus (BYDV), one of the most widespread and damaging viruses of small grains, is transmitted by cereal aphids and has a broad range of cultivated and uncultivated hosts from the Poaceae family. Here, we examined the effects of elevated CO2 on plant physiology, Rhopalosiphum padi L. performance, and the accumulation of BYDV (strain BYDV-PAV) in winter wheat (Triticum aestivum L.), foxtail barley (Hordeum jubatum L.), and green foxtail (Setaria viridis (L.) Beauv.). A growth chamber experiment was conducted under ambient (420 ppm) and elevated CO2 (700 ppm) with aphid-infested and uninfested plants. Elevated CO2 significantly increased total plant biomass in all species but did not affect aphid survival or reproduction. The root biomass of winter wheat and foxtail barley, but not green foxtail, increased under elevated CO2. However, no significant effect of aphids/BYDV was detected on total plant biomass. Transpiration rates varied with host plant and aphid presence but were not affected by CO2 level. Total water-soluble carbohydrate concentration was unaffected by CO2 or aphids. BYDV-PAV accumulation varied by host plant species, with winter wheat having the highest virus titer, followed by foxtail barley and green foxtail. Virus titers were increased under elevated CO2 in all host plant species. We demonstrated that uncultivated grasses are important reservoirs for both BYDV-PAV and the R. padi vector and suggested that elevated CO2 may enhance virus accumulation across the evaluated host plants. This underscores the need to consider the role of non-crop hosts in developing management plans and/or predicting BYDV dynamics in small grains.

The English grain aphid (Sitobion avenae) threatens wheat production through direct feeding and indirectly as a virus vector (e.g., barley yellow dwarf virus - BYDV). Aphid management still relies predominantly on insecticides, an increasingly unsustainable practice; however, host-plant resistance is a promising solution to manage aphids and the viruses that they transmit. Resistance has been recently identified in the ancestor wheat Triticum monococcum MDR045 and MDR049 against S. avenae and Rhopalosiphum padi. In this study, we investigated whether foliar chemistry plays a role in this resistance against S. avenae. Foliar extracts from T. monococcum MDR045 and MDR049 reduced S. avenae survival in artificial feeding assays. Activity was aphid density-dependent, and systemic responses were limited to the leaf of the aphid feeding site, following 24 h of aphid herbivory. Bioassay-guided fractionation isolated saponarin, a diglycosyl flavone, as an allelochemical involved in this activity. Saponarin activity was similar to naringenin but unique compared to other plant flavonoids tested. Implications of these findings for effective aphid and virus management are discussed.