Bird Cherry-oat Aphid Rhopalosiphum Padi Research Articles

Genetic diversity in vector populations influences the transmission efficiency of an important plant virus.

The transmission efficiency of aphid-vectored plant viruses can differ between aphid populations. Intra-species diversity (genetic variation, endosymbionts) is a key determinant of aphid phenotype; however, the extent to which intra-species diversity contributes towards variation in virus transmission efficiency is unclear. Here, we use multiple populations of two key aphid species that vector barley yellow dwarf virus (BYDV) strain PAV (BYDV-PAV), the grain aphid (Sitobion avenae) and the bird cherry-oat aphid (Rhopalosiphum padi), and examine how diversity in vector populations influences virus transmission efficiency. We use Illumina sequencing to characterize genetic and endosymbiont variation in multiple Si. avenae and Rh. padi populations and conduct BYDV-PAV transmission experiments to identify links between intra-species diversity in the vector and virus transmission efficiency. We observe limited variation in the transmission efficiency of Si. avenae, with transmission efficiency consistently low for this species. However, for Rh. padi, we observe a range of transmission efficiencies and show that BYDV transmission efficiency is influenced by genetic diversity within the vector, identifying 542 single nucleotide polymorphisms that potentially contribute towards variable transmission efficiency in Rh. padi. Our results represent an important advancement in our understanding of the relationship between genetic diversity, vector-virus interactions, and virus transmission efficiency.

The Effect of Essential Oils from Asteraceae Plants on Behavior and Selected Physiological Parameters of the Bird Cherry-Oat Aphid.

Essential oils (EOs), including those from the Asteraceae plants, have been shown to have promising insecticidal activity against a wide range of insect pests. Understanding the mechanism of action of EOs is one of the studied aspects. The present study aimed to evaluate the effect of essential oils from Achillea millefolium, Santolina chamaecyparissus, Tagetes patula and Tanacetum vulgare on the settling and probing behavior of the bird cherry-oat aphid (Rhopalosiphum padi L.). In addition, the effect of the oils on the activity of such enzymes as trypsin, pepsin and α- and β-glucosidase involved in the metabolism of proteins and sugars of the insects was examined. The leaf-choice bioassays demonstrated that the studied EOs limited aphid settling for at least 24 h after the treatment. The application of EOs also inferred with aphid probing behavior by reducing the total probing time and total duration of phloem sap ingestion. Aphids spent more time in the search phase due to an increase in the number and total duration of pathway phases. Moreover, the activity of the studied proteases and glucosidases significantly decreased in R. padi females exposed to the EOs. The enzyme inhibition varied depending on the applied oil and exposure time. Generally, the EOs with stronger deterrent activity also showed higher inhibitory effects. The results suggest that the tested EOs disrupt key digestive processes in R. padi which may be an important factor determining their aphicidal activity.

Bacillus subtilis 26D Triggers Induced Systemic Resistance against Rhopalosiphum padi L. by Regulating the Expression of Genes AGO, DCL and microRNA in Bread Spring Wheat.

Bacillus subtilis 26D is a plant growth-promoting endophytic bacteria capable of inducing systemic resistance through the priming mechanism, which includes plant genome reprogramming and the phenomenon of RNA interference (RNAi) and microRNA (miRNAs). The phloem-feeding insect bird cherry-oat aphid Rhopalosiphum padi L. is a serious pest that causes significant damage to crops throughout the world. However, the function of plant miRNAs in the response to aphid infestation remains unclear. The results of this work showed that B. subtilis 26D stimulated aphid resistance in wheat plants, inducing the expression of genes of hormonal signaling pathways ICS, WRKY13, PR1, ACS, EIN3, PR3, and ABI5. In addition, B. subtilis 26D activated the RNAi mechanism and regulated the expression of nine conserved miRNAs through activation of the ethylene, salicylic acid (SA), and abscisic acid (ABA) signaling pathways, which was demonstrated by using treatments with phytohormones. Treatment of plants with SA, ethylene, and ABA acted in a similar manner to B. subtilis 26D on induction of the expression of the AGO4, AGO5 and DCL2, DCL4 genes, as well as the expression of nine conserved miRNAs. Different patterns of miRNA expression were found in aphid-infested plants and in plants treated with B. subtilis 26D or SA, ethylene, and ABA and infested by aphids, suggesting that miRNAs play multiple roles in the plant response to phloem-feeding insects, associated with effects on hormonal signaling pathways, redox metabolism, and the synthesis of secondary metabolites. Our study provides new data to further elucidate the fine mechanisms of bacterial-induced priming. However, further extensive work is needed to fully unravel these mechanisms.

The biosynthesis of alarm pheromone in the wheat aphid Rhopalo-siphum padi is regulated by hormones via fatty acid metabolism

Aphids are major insect pests in agriculture and forestry worldwide. Following attacks by natural enemies, many aphids release an alarm pheromone to protect their population. In most aphids, the main component of the aphid alarm pheromone (AAP) is the sesquiterpene hydrocarbon (E)-β-farnesene (EβF). However, the mechanisms behind its biosynthesis and regulation remain poorly understood. In this study, we used the bird cherry–oat aphid Rhopalosiphum padi, which is an important wheat aphid, to investigate the regulatory mechanisms of EβF biosynthesis. Our results showed that EβF biosynthesis occurs during the mature embryo period and the molting period of the 1st- and 2nd-instar nymphs. Triglycerides provide the prerequisite material for EβF production and release. Based on transcriptome sequencing, RNAi analysis, hormone treatments, and quantitative measurements, we found that the biosynthesis of EβF utilizes acetyl coenzyme A produced from fatty acid degradation, which can be suppressed by juvenile hormone but it is promoted by 20-hydroxyecdysone through the modulation of fatty acid metabolism. This is the first systemic study on the modulation of EβF production in aphids. The results of our study provide insights into the molecular regulatory mechanisms of AAP biosynthesis, as well as valuable information for designing potential aphid control strategies.

Aphid Species Composition in Three Parks of Saint-Petersburg and Leningrad Region in 2021

Due to the high harmfulness of aphids inhabiting trees and shrubs in the St. Petersburg’s and the Leningrad Region’s park areas, it becomes necessary to monitor the dynamics of the numbers and species composition of this group of insects. During the vegetation season of 2021, the species composition of aphids was determined in three parks in St. Petersburg and the Leningrad Region: Sosnovsky forest park, Pavlovsky and Gatchina parks. The material was taken directly from plants and caught using an entomological net. A total of 16 species were identified. In the Sosnovsky forest park, 10 species were identified, in the Pavlovsky park – 12, in the Gatchinsky park – 9 species. Two species were found on coniferous trees, the rest – on the deciduous ones. Species such as dogwood aphid (Anoecia corni F.), bird cherry-oat aphid (Rhopalosiphum padi L.), silver birch aphid (E-uceraphis betulae gr. sp.), common oak aphid (Tuberculatus annulatus Hart.), black bean aphid (Aphis fabae Scop.), rose aphid (Macrosiphum rosae L.) were found in all three parks, the rest – in one or two parks. Dogwood aphid, bird cherry-oat aphid, silver birch aphid, black bean aphid and rose aphid were observed in massively large colonies on a significant number of host trees. In other species, small colonies were found on separate trees; finally, for some species only single individuals were caught. In the first half of September, the number of aphids was relatively low.

Entomophthoralean fungi overwinter with the bird cherry-oat aphid on bird cherry trees

In Scandinavia, the bird cherry-oat aphid Rhopalosiphum padi overwinter as eggs on the bird cherry tree Prunus padus. Branches of P. padus were collected at the late February / early March from 17 locations in Norway over a three-year period. We found 3599 overwintering aphid eggs, 59.5% of which were dead. Further, a total of 879 overwintering fungus-killed cadavers were observed. These cadavers were found close to bud axils, where overwintering eggs were also usually attached. Cadavers were infected with either Zoophthora cf. aphidis or Entomophthora planchoniana. All the fungal-killed cadavers were filled with overwintering structures of Z. cf. aphidis (as resting spores) or E. planchoniana (as modified hyphal bodies). We found a significant negative correlation between eggs and cadavers per branch. However, both numbers of eggs and cadavers varied greatly between years and among tree locations. This is the first report of E. planchoniana overwintering in R. padi cadavers as modified hyphal bodies. We discuss whether P. padus may act as an inoculum reservoir for fungi infecting aphids in cereals in spring.

Differential Susceptibility of Coleomegilla maculata and Scymnus creperus Larvae to Aggression by Solenopsis invicta Workers.

The biological control of aphids by aphidophagous coccinellids is often hampered by aphid-tending ants or aggressive, invasive ants foraging for food. Aggressive species such as the imported fire ant Solenopsis invicta Buren may attack and kill coccinellid larvae. This study tested the hypothesis that wax-secreting Scymnus creperus Mulsant larvae are less susceptible than non-wax-secreting Coleomegilla maculata (DeGeer) larvae to S. invicta aggression. Laboratory experiments were set up using bird cherry-oat aphid Rhopalosiphum padi (L.) nymphs and adults (as prey for coccinellids) on barley leaves in arenas with either coccinellid species and with or without S. invicta workers. The presence of S. invicta reduced aphid predation by C. maculata but not Sc. creperus. The frequency of S. invicta attack was greater for C. maculata than Sc. creperus; mortality was significantly greater for C. maculata than Sc. creperus. The wax covering on Sc. creperus reduced S. invicta aggression. Unexpectedly, Sc. creperus larvae with the wax cover removed did not suffer more S. invicta attacks or increased mortality. In conclusion, the wax cover and, perhaps, the volatile or non-volatile compounds in the wax and on the integument of Sc. creperus larvae reduce S. invicta aggression. Further research could identify the wax compounds and determine their functionality as semiochemicals against S. invicta.

Chemosensory proteins are associated with thiamethoxam tolerance in bird cherry-oat aphid Rhopalosiphum padi

Rhopalosiphum padi (L.) is an important cosmopolitan pest of cereal crops. Thiamethoxam is widely used for control R. padi in some regions. Chemosensory proteins (CSPs) are a class of transporter proteins in arthropods which play a key role in various physiological processes including response to insecticide exposure. However, the role of R. padi CSPs (RpCSPs) in insecticide binding and susceptibility has not been well clarified. In this study, we found that the expression levels of RpCSP1, RpCSP4, RpCSP5, RpCSP7, RpCSP10 were dramatically upregulated after exposure to thiamethoxam. Suppression of RpCSP4 and RpCSP5 transcription by RNA interference significantly enhanced the susceptibility of R. padi to thiamethoxam. Molecular docking and fluorescence competitive binding showed that RpCSP4 and RpCSP5 had high binding affinity with thiamethoxam. The present results prove that RpCSP4 and RpCSP5 are related to insecticide resistance through high binding affinity to reduce the toxicity of insecticide.

Volatile interactions between specific undamaged barley cultivars affect aphid feeding behavior and performance

Recent studies have demonstrated that cultivar mixtures can reduce aphid plant acceptance and population development. It is still unknown as to which underlying mechanisms may contribute to this phenomenon. We investigated the effects of volatile interactions between undamaged barley cultivars on aphid feeding behavior and performance in the laboratory. Spring barley (Hordeum vulgare L.) cultivar Salome was exposed to volatiles from Fairytale (SeF), Anakin (SeA), or clean air (Se0). We used an electrical penetration graph to test the effect of exposure to neighbor volatiles on the feeding behavior and performance of bird cherry-oat aphids (Rhopalosiphum padi L.). We also assessed aphid relative growth rate, intrinsic rate of increase, and development time on exposed and unexposed Salome plants. Aphids spent significantly longer time on epidermis and mesophyll plant tissues on SeF than Se0, and no difference was observed between SeA and Se0. Significant decreases in the duration of phloem ingestion and phloem sustained ingestion were recorded in SeF showing that volatile-induced effects cause difficulty for aphids to feed. However, no differences in these variables were detected between SeA and Se0. We also observed reduced aphid relative growth rate and intrinsic rate of increase on SeF compared to Se0 and SeA. Our study demonstrated that, in a specific combination, exposure of one barley cultivar to volatiles from another one can change aphid feeding behavior and performance, probably due to changes in host plant properties/quality. Our results provide an insightful explanation of mechanisms responsible for the reduced aphid population development previously observed in the field.

Analysis of the Genetic Diversity of Two Rhopalosiphum Species from China and Europe Based on Nuclear and Mitochondrial Genes

Population genetic studies can reveal clues about the evolution of adaptive strategies of aphid species in agroecosystems and demonstrate the influence of environmental factors on the genetic diversity and gene flow among aphid populations. To investigate the genetic diversity of two Rhopalosiphum aphid species from different geographical regions, 32 populations (n = 535) of the bird cherry-oat aphid (Rhopalosiphum padi Linnaeus) and 38 populations (n = 808) of the corn leaf aphid (Rhopalosiphum maidis Fitch) from China and Europe were analyzed using one nuclear (elongation factor-1 alpha) and two mitochondrial (cytochrome oxidase I and II) genes. Based on the COI-COII sequencing, two obvious clades between Chinese and European populations and a low level of gene flow (Nm = 0.15) were detected in R. padi, while no geographical-associated genetic variation was found for EF-1α in this species. All genes in R. maidis had low genetic variation, indicating a high level of gene flow (Nm = 5.31 of COI-COII and Nm = 2.89 of EF-1α). Based on the mitochondrial result of R. padi, we concluded that the long distance between China and Europe may be interrupting the gene flow. The discordant results of nuclear gene analyses in R. padi may be due to the slower evolution of nuclear genes compared to mitochondrial genes. The gene exchange may occur gradually with the potential for continuous migration of the aphid. This study facilitates the design of control strategies for these pests.

Effect of High Temperature and Natural Enemies on the Interspecies Competition Between Two Wheat Aphid Species, Rhopalosiphum padi and Sitobion miscanthi.

Interspecies competition affects the distribution, quantity, and community structure of insects, especially among closely-related (congeners) species. Some ecological factors differentially affect the fitness of co-existing species, thus conferring an advantage on one competitor, and then the structure of communities. The present work evaluated the effects of high temperature and natural enemies on the interspecific competition between the grain aphid Sitobion miscanthi (Takahashi) (Aphididae: Hemiptera) and bird cherry-oat aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae), two key pests of wheat in China. Results showed that the population growth of R. padi was faster at 30°C, and the intrinsic rate of natural increase (rm) value was 5 times that of S. miscanthi, indicating that R. padi was more high-temperature resistant and has advantages in interspecific competition at high temperature. Moreover, compared to S. miscanthi, the population of R. padi was less affected by their predator, larvae of the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), and aphid parasitoids, Aphidius avenae (Haliday) or Aphidius gifuensis (Ashmead) (Hymenoptera: Aphidiidae), which made them gain an advantage in the interspecific competition. Our results enrich the knowledge of phytophagous insect interspecific completion and implicate the ecological mechanism of R. padi may become the dominant species in wheat fields in China.

Effects of Methyl Salicylate on Host Plant Acceptance and Feeding by the Aphid Rhopalosiphum padi.

Methyl salicylate (MeSA) is a volatile shown to act as an inducer of plant defense against pathogens and certain herbivores, particularly aphids. It has been shown to have potential for aphid pest management, but knowledge on its mode of action is lacking, particularly induced plant-mediated effects. This study investigated the effects of exposing plants to MeSA on the host searching, host acceptance and feeding behavior of the bird cherry-oat aphid Rhopalosiphum padi. Barley plants were exposed to volatile MeSA for 24 h, after which biological effects were tested immediately after the exposure (Day 0), and then 1, 3 and 5 days after the end of the exposure. Aphid settling on MeSA-exposed plants was significantly reduced on days 0, 1 and 3, but not on day 5. In olfactometer tests, aphids preferred the odor of unexposed plants on days 1 and 3, but not on day 0 or 5. Analysis of volatiles from exposed and unexposed plants showed higher levels of MeSA from exposed plants, most likely absorbed and re-released from plant surfaces, but also specific changes in other plant volatiles on days 0, 1 and 3. High doses of MeSA did not affect aphid orientation in an olfactometer, but lower doses were repellent. Analysis of aphid feeding by Electronic penetration graph (EPG) showed that MeSA exposure resulted in resistance factors in barley plants, including surface factors and induced systemic factors in other tissues including the phloem. The results support the potential of MeSA as a potential tool for management of aphid pests.

The Effectiveness of Physical and Chemical Defense Responses of Wild Emmer Wheat Against Aphids Depends on Leaf Position and Genotype.

The bird cherry-oat aphid (Rhopalosiphum padi) is one of the most destructive insect pests in wheat production. To reduce aphid damage, wheat plants have evolved various chemical and physical defense mechanisms. Although these mechanisms have been frequently reported, much less is known about their effectiveness. The tetraploid wild emmer wheat (WEW; Triticum turgidum ssp. dicoccoides), one of the progenitors of domesticated wheat, possesses untapped resources from its numerous desirable traits, including insect resistance. The goal of this research was to determine the effectiveness of trichomes (physical defense) and benzoxazinoids (BXDs; chemical defense) in aphid resistance by exploiting the natural diversity of WEW. We integrated a large dataset composed of trichome density and BXD abundance across wheat genotypes, different leaf positions, conditions (constitutive and aphid-induced), and tissues (whole leaf and phloem sap). First, we evaluated aphid reproduction on 203 wheat accessions and found large variation in this trait. Then, we chose eight WEW genotypes and one domesticated durum wheat cultivar for detailed quantification of the defense mechanisms across three leaves. We discovered that these defense mechanisms are influenced by both leaf position and genotype, where aphid reproduction was the highest on leaf-1 (the oldest), and trichome density was the lowest. We compared the changes in trichome density and BXD levels upon aphid infestation and found only minor changes relative to untreated plants. This suggests that the defense mechanisms in the whole leaf are primarily anticipatory and unlikely to contribute to aphid-induced defense. Next, we quantified BXD levels in the phloem sap and detected a significant induction of two compounds upon aphid infestation. Moreover, evaluating aphid feeding patterns showed that aphids prefer to feed on the oldest leaf. These findings revealed the dynamic response at the whole leaf and phloem levels that altered aphid feeding and reproduction. Overall, they suggested that trichomes and the BXD 2,4-dihydroxy-7- methoxy-1,4-benzoxazin-3-one (DIMBOA) levels are the main factors determining aphid resistance, while trichomes are more effective than BXDs. Accessions from the WEW germplasm, rich with trichomes and BXDs, can be used as new genetic sources to improve the resistance of elite wheat cultivars.

Direct and Knock-on Effects of Water Stress on the Nutrient Contents of Triticum aestivum (Poales: Poaceae) and Population Growth of Rhopalosiphum padi (Hemiptera: Aphididae).

To ascertain the direct effects of water stress upon wheat plants (Triticum aestivum L.) and how these effects, in turn, influence the population growth of the bird cherry-oat aphid (Rhopalosiphum padi L.), we conducted a physiological analysis of wheat seedlings grown under three different watering regimes and subsequently determined the population parameters of the aphid using the age-stage, two-sex life table. A significantly higher content of free amino acids and soluble sugars were observed in wheat seedlings exposed to drought stress compared to seedlings that were well-watered and those that were grown under waterlogged conditions. Extended phloem salivation and stylet penetration with shorter duration of sustained ingestion from phloem was observed in an electrical penetration graph (EPG) of R. padi on drought-stressed wheat seedlings. This suggested that the aphid's feeding activity, as well as nutrient intake, were impeded. The significantly higher percentage of essential amino acids found in wheat seedlings grown under waterlogged conditions promoted significantly higher fecundity and intrinsic rate of increase in R. padi populations compared to aphids fed on drought-treated or well-watered wheat seedlings. Our findings suggest that wheat seedling responses to water stress involve changes in sap composition that are responsible for altering the aphids' nutrient intake and consequently affect their population growth. From a grower's perspective, extending wheat cultivation in a rice-wheat rotation paddy field during the winter season may not be economically profitable if the fields are chronically waterlogged, since this may potentially lead to a higher infestation of cereal aphids.

The Effect of Santolina chamaecyparissus and Tagetes patula Essential Oils on Biochemical Markers of Oxidative Stress in Aphids

Simple SummaryDue to numerous side effects associated with extensive use of chemical insecticides, there is a need to develop eco-friendly alternative methods for insect pest control. One of these alternatives may be the use of essential oils (EOs). An important aspect of the efficient and safe application of EOs in plant protection is the elucidation of their toxicity mechanisms towards target pests. The present study aimed to determine the effects of Santolina chamaecyparissus (L.) and Tagetes patula (L.) EOs on development and physiology of two aphid species with different feeding specializations. Myzus persicae (Sulzer) is a broad generalist and Rhopalosiphum padi (L.) is a grass specialist. Exposure to the tested EOs limited the aphids’ development and led to induction of oxidative stress within their tissues. Analysis of the physiological parameters also showed that the oligophagous R. padi was more sensitive to EO treatment than the highly polyphagous M. persicae. The results suggest that the tested EOs can affect important biochemical processes within aphid tissues and have potential as eco-friendly aphicides.This study investigated the toxicity of essential oils (EOs) from Santolina chamaecyparissus (L.) and Tagetes patula (L.) towards the green peach aphid Myzus persicae (Sulzer) and the bird cherry-oat aphid Rhopalosiphum padi (L.). The effects of the EOs on aphid population parameters and levels of biochemical markers of oxidative stress within insect tissues were analyzed. In laboratory bioassays, application of the studied EOs at sublethal concentrations reduced daily fecundity and led to a decrease in the intrinsic rate of natural increase in both aphid species. Treatment with EOs also induced generation of reactive oxygen species (ROS) within aphid tissues. The highest levels of superoxide anion and hydrogen peroxide were noted after 24 and 48 h of exposure. Moreover, a significant increase in lipid peroxidation was shown in treated aphids, especially between 48 and 72 h after exposure. The increase was more pronounced after treatment with the essential oil of S. chamaecyparissus, which also exhibited higher aphicidal activity in toxicity tests. The activities of antioxidant enzymes—superoxide dismutase (SOD) and catalase (CAT)—were significantly elevated in both aphid species in response to the tested EOs. The obtained results suggest that oxidative stress evoked by treatment with the studied EOs may be an important factor determining their toxicity towards aphids.

Impact of Pests on Cereal Grain and Nutrient Yield in Boreal Growing Conditions

The effect of weeds, plant diseases and insect pests on spring barley (Hordeum vulgare) and spring wheat (Triticum aestivum) grain and nutrient yield was examined. Long-term field trial data was used to assess the impact of different pests on grain yield. In the absence of pesticides, fungal diseases caused the largest annual yield-reduction in spring wheat and spring barley, 500 kg ha−1 on average. Converting yield loss to nutrient yield loss this represented reductions of 8.1 and 9.2 kg ha−1 in nitrogen and 1.5 and 1.6 kg ha−1 in phosphorus, respectively. Likewise, it was estimated that weeds decrease the yield of spring barley and spring wheat for 200 kg ha−1, which means reductions of 3.7 and 3.2 kg ha−1 in nitrogen and 0.6 kg ha−1 in phosphorus, respectively. For insect pests yield-reduction in spring barley and spring wheat varied between 418 and 745 kg ha−1 respectively. However, because bird cherry-oat aphid (Rhopalosiphum padi L.) incidence data was limited, and aphids are highly variable annually, nutrient yield losses caused by insect pests were not included. Based on the current study, the management of weeds, plant diseases and insects maintain cereal crop yield and may thus decrease the environmental risks caused by unutilized nutrients.

Effect of the cereal aphid infestation on the oxidative damages of protein in the maize (Zea mays L.)

We studied the effect of the cereal aphid (the bird cherry-oat aphid Rhopalosiphum padi L. and grain aphid Sitobion avenae F.) infestations on the oxidative damages of protein in the maize (Zea mays L., cultivar Touran) seedlings. We found that the content of protein thiols and protein bound carbonyls were dependent from study factors: time of feeding, the number of aphids and species. In relation to uninfested plants (control), prolonged insect (R. padi and S. avenae) feeding (24–96 h post infestations) was linked to depletion in levels of protein thiols in foliar tissues of maize genotype and accumulation after 96 h post infestations in maize seedlings investigated by higher number of aphids, protein bound carbonyls. Our results indicated that the biotic stress factors, including aphids evoke the oxidation of protein in the maize. The stronger protein damages occurred in the maize seedlings infested with oligophagous R .padi females.

Host-targeted salt stress affects fitness and vector performance of bird cherry-oat aphid (Rhopalosiphum padi L.) on wheat

Salinity is becoming a limiting factor for crop production, particularly in arid and semiarid areas all around the world. This phenomenon can adversely affect both plant integrity and herbivorous insects. Herein, we assessed the bottom-up effects of four salinity levels (3.1 [control], 6.0, 10 and 12.0 dS/m) on the life parameters of viruliferous bird cherry-oat aphid (Rhopalosiphum padi L.) and the aphid transmission of Barley yellow dwarf virus-PAV (BYDV-PAV) to wheat host. The results revealed that nymph longevity and adult pre-oviposition period of the aphids fed on salinity-stressed plants were significantly increased, while adult longevity, gross reproductive rate, net reproductive rate, intrinsic rate of increase and finite rate of increase of the aphids on plants challenged with salinity levels of 10 and 12.0 dS/m were significantly reduced. Also, survival rate and life expectancy of viruliferous R. padi remarkably decreased on wheat plants under 10 and 12.0 dS/m salinity. The R. padi-mediated transmission of BYDV-PAV to salinity-stressed (10 and 12.0 dS/m) wheat plants was significantly reduced. Moreover, the biochemical assays showed a significant increase in biosynthesis of phenolics and free proline within wheat plants challenged with salinity stress. Based on these findings, it can be concluded that salinity stress negatively influences life parameters of viruliferous R. padi, possibly through induction of phenolics and free proline within the salinity-stressed plants, and the aphid transmission of BYDV-PAV to wheat host.

Grassy Weeds and Corn as Potential Sources of Barley yellow dwarf virus Spread Into Winter Wheat.

Barley yellow dwarf virus (BYDV) is an important vector-borne pathogen of cereals. Although many species of grasses are known to host BYDV, knowledge of their role in virus spread in regional agroecosystems remains limited. Between 2012 and 2016, Idaho winter wheat production was affected by BYDV. BYDV-PAV and the bird cherry-oat aphid (BCOA) (Rhopalosiphum padi L.) vector were commonly present in the affected areas. A series of greenhouse bioassays were performed to examine whether two types of corn (Zea mays L.), dent and sweet, and three commonly found grassy weeds, downy brome (Bromus tectorum L.), green foxtail (Setaria viridis L.), and foxtail barley (Hordeum jubatum L.), can be inoculated with BYDV (species BYDV-PAV) by BCOA and also act as sources of the virus in winter wheat. BCOA successfully transmitted BYDV-PAV to both corn types and all weed species. Virus titers differed between the weed species (P = 0.032) and between corn types (P = 0.001). In transmission bioassays, aphids were able to survive on these host plants during the 5-day acquisition access period and later successfully transmitted BYDV-PAV to winter wheat (var. SY Ovation). Transmission success was positively correlated with the virus titer of the source plant (P < 0.001) and influenced by weed species (P = 0.028) but not corn type. Overall, the results of our inoculation and transmission assays showed that the examined weed species and corn types can be inoculated with BYDV-PAV by BCOA and subsequently act as sources of infections in winter wheat.

Biosynthesis of aphid alarm pheromone is modulated in response to starvation stress under regulation by the insulin, glycolysis and isoprenoid pathways

The mechanism for biosynthesis and molecular regulation of the aphid alarm pheromone (AAP) is still a mystery. Previous studies indicated that the biosynthesis of AAP was directly affected by the terpenoid backbone biosynthesis pathway, and several pathways involved in nutritional metabolism providing the bricks for AAP biosynthesis were up-regulated in response to simulated stimulation. This suggests that AAP biosynthesis might be regulated by complex metabolic pathways. Here the molecular responses of the bird cherry-oat aphid Rhopalosiphum padi to starvation stress were investigated, and the molecular pathways were further analyzed by using RNA interference (RNAi) and protein inhibitor, combined with gas chromatography–mass spectrometry analysis of (E)-β-farnesene (EβF), the major component of the alarm pheromone in R. padi. The results showed that the nutritional stress significantly reduced the weight of aphid and the quantity of EβF, and meanwhile dramatically up-regulated the insulin receptor genes (InsR1/2) and down-regulated the downstream genes encoding the kinases PI3K and Akt, key enzymes in the glycolysis pathway (HK, A6PFK, PK) and the isoprenoid pathway (ACSS, HMGR, FPPS1, FPPS2, GGPPS, DPPS). PI3K inhibitor LY294002 treatment and RNAi-mediated knockdown of InsR1/2 significantly reduced the expression level of downstream genes and the quantity of EβF. Furthermore, knockdown of PK, the rate-limiting enzyme in the glycolysis pathway, down-regulated the genes in the isoprenoid pathway and the production of EβF; knockdown of the genes encoding isoprenyl diphosphate enzymes revealed that FPPS1 and FPPS2 were both required for EβF biosynthesis. Our data suggested that AAP is synthesized via glycolysis and isoprenoid pathways under regulation by the insulin signaling pathway.