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The alfalfa virome has been understudied. Existing research dealing with viral incidences within the crop primarily concentrate on local factors, rather than considering a broader perspective. In this comprehensive 2‐year study, we define the alfalfa virome and the main local and landscape factors affecting the incidence and annual increase of the Alfalfa mosaic virus (AMV), the most prevalent virus in alfalfa. The study was conducted in commercial alfalfa fields located along the highly productive northeast region of the Iberian Peninsula. For the first time in Europe, next‐generation sequencing revealed the presence of 14 different viruses representing the genera Cytorhabdovirus, Alphapartitivirus, Amalgavirus, Alfamovirus, Luteovirus, Enamovirus and Flavivirus. AMV was the most prevalent species, accounting for 89% of the identified viral contigs. Enzyme‐linked immunosorbent assays showed that the incidence of AMV varied between fields, with the average incidence doubling from 34% in 2019 to 65% in 2020. To assess the effect of local and landscape characteristics on the incidence of AMV and the observed annual increase, we selected different local variables and recorded landscape structure at three different buffer radii (250, 500 and 1000 m) from the centre of each field. Both the incidence and annual increase in AMV were driven mainly by local characteristics. The incidence of AMV showed a significant relationship with crop age and field area, whereas the annual increase was mainly influenced by crop age and the cumulative number of alate morphs of the aphid Acyrthosiphon pisum. Only one landscape composition variable, the percentage of alfalfa, showed a significant relationship with AMV incidence at the 250‐m scale. These results confirm the effect of local variables on the population structure of generalist viruses. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Arbuscular mycorrhizal fungi (AMF) impact the relationships between plants, aphids (insects that feed on plant phloem), and their natural enemies (insects that prey on or parasitize aphids). The presence of AMF influences the growth and population of different aphid species and affects the development of aphid‐killing wasps and their attraction to plants. This research has been conducted also considering the insects' feeding strategy and their feeding specialization. This study provides novel perspectives on how these fungi shape interactions in the natural world, offering potential insights for the development of sustainable pest management strategies in agriculture. Summary: Arbuscular mycorrhizal fungi (AMF) are major root symbionts regulating plant physiology. Their presence affects the performance of aboveground insect herbivores in relation to their feeding strategy and their feeding specialization. For example, the effect of the arbuscular mycorrhizal (AM) symbiosis on chewing insects, positive for specialists and negative for generalists, has been previously demonstrated. Conversely, the impact of AMF on phloem‐suckers with relatively different levels of specialization remains unexplored.We tested the influence of the AM Funneliformis mosseae on the fitness of the specialist aphid Acyrthosiphon pisum and the generalist aphid Myzus persicae on Vicia faba plants. Further, we investigated the effects of AMF on the higher trophic level, the aphid parasitoids Aphidius ervi (specialist) and Aphidius colemani (generalist), by evaluating plant attractiveness and parasitoid fitness. To support the results of behavioral and biological bioassays we characterized the photosynthetic parameters, the volatilome and the transcriptome of tested plants.Mycorrhizal plants proved unsuitable for the generalist M. persicae but enhanced the fitness of the specialist A. pisum. The AM symbiosis had no effects on the behavioral response of A. colemani and enhanced the attraction and fitness of A. ervi.Volatilome and transcriptome profiling corroborated the results of bioassay highlighting a bottom‐up effect of the AMF across a plant–aphid–parasitoid system. [ABSTRACT FROM AUTHOR]

Soybean dwarf virus (SbDV; family Tombusviridae, genus Luteovirus, species Luteovirus glycinis) is an RNA plant virus that is transmitted solely by aphids in a persistent, circulative and non-propagative manner. SbDV causes significant losses in cultivated Fabaceae, especially in subterranean clover (Trifolium subterraneum) pastures of mainland Australia. SbDV isolates are classified into four phenotypically distinguishable strains: YP, YS, DP, and DS. Y and D strains differ primarily in their host range, and P and S strains in their primary vector species. Genetically, Y and D strains separate into two clades in every genomic region except for the N-terminal region of the readthrough domain (N-RTD), in which P and S strains separate. SbDV diversity in Australia has yet to be investigated, so in this study, 41 isolates were collected from six different host species across two production regions of Australia: the south coast of Western Australia ('south-west') and northern New South Wales/southern Queensland ('north-east'). A near-complete genome sequence of each isolate was obtained, and together with all 50 whole-genome sequences available in the GenBank database, underwent phylogenetic analysis of the whole genome nt and the N-RTD aa sequences. At the whole-genome level, the isolates separated into D and Y clades. At the N-RTD level, most of the isolates separated into P and S clades. All south-west isolates and 11 of the 31 north-east isolates were in the Y clade, and the remaining 20 north-east isolates were in the D clade. Except for one isolate that fell outside the P and S clades, all south-west and north-east isolates were in the P clade, suggesting that they are transmitted by Acyrthosiphon pisum and Myzus persicae. Available biological data largely supported the phenotypic inferences made from the phylogenetic analysis, suggesting that genetic data can provide critical epidemiological insights, provided that sufficient biological data have been collected. [ABSTRACT FROM AUTHOR]

Aphids, the important global agricultural pests, harbor abundant resources of symbionts that can improve the host adaptability to environmental conditions, also control the interactions between host aphid and natural enemy, resulting in a significant decrease in efficiency of biological control. The facultative symbiont Serratia symbiotica has a strong symbiotic association with its aphid hosts, a relationship that is known to interfere with host–parasitoid interactions. We hypothesized that Serratia may also influence other trophic interactions by interfering with the physiology and behavior of major predators to provide host aphid defense. To test this hypothesis, we investigated the effects of Serratia on the host aphid Acyrthosiphon pisum and its predator, the ladybeetle Propylaea japonica. First, the prevalence of Serratia in different A. pisum colonies was confirmed by amplicon sequencing. We then showed that harboring Serratia improved host aphid growth and fecundity but reduced longevity. Finally, our research demonstrated that Serratia defends aphids against P. japonica by impeding the predator's development and predation capacity, and modulating its foraging behavior. Our findings reveal that facultative symbiont Serratia improves aphid fitness by disrupting the predation strategy of ladybeetle larvae, offering new insight into the interactions between aphids and their predators, and providing the basis of a new biological control strategy for aphid pests involving the targeting of endosymbionts. [ABSTRACT FROM AUTHOR]

ABSTRACT Aphids are serious insect pests for agricultural and horticultural crops and may cause the major economic losses. Insecticides used to control aphids have caused environmental pollution and the insecticide residues in agricultural products. A new protease inhibitor gene from bacterium Xenorhabdus bovienii (Xbpi‐1) and the protease inhibitor protein expressed by the gene against the pea aphid (Acyrthosiphon pisum Harris; Hemiptera: Aphididae) have been reported, however, effects of the PIP on the symbiotic bacteria, Buchnera aphidicola, and gene expression in pea aphids are unknown. By assessing the quantity of B. aphidicola, the primary symbiotic bacterium, in the aphid fed on an artificial diet containing 100 and 500 μg/mL Xbpi‐1, we observed a substantial reduction in its population by 27% and 46%, respectively, as analysed by real‐time quantitative reverse transcription PCR (qRT‐PCR). Furthermore, the growth of other aphid‐associated bacteria was also significantly inhibited by Xbpi‐1. To elucidate the mechanisms at the gene level, we conducted transcriptome analysis and identified differentially expressed genes (DEGs). Subsequent Gene Ontology (GO) analysis of the 213 DEGs shed light on the impact of Xbpi‐1 on aphid metabolism processes and gene expression. Notably, the results highlighted several aphid nutrient metabolism pathways affected by Xbpi‐1, which are relevant to vector‐borne diseases. These pathways encompass crucial factors such as heat shock proteins, cuticle proteins and proteases. The results from this study revealed that the PIP had a novel mechanism against pea aphids by having adverse effects on the primary symbiotic bacteria in pea aphids and affecting aphid gene expression, showing that the PIP may be a promise bioinsecticide for aphid control in the future. [ABSTRACT FROM AUTHOR]

Epigenetic mechanisms, such as DNA methylation, have been proposed to mediate plastic responses in insects. The pea aphid (Acyrthosiphon pisum), like the majority of extant aphids, displays cyclical parthenogenesis ‐ the ability of mothers to switch the reproductive mode of their offspring from reproducing parthenogenetically to sexually in response to environmental cues. The pea aphid genome encodes two paralogs of the de novo DNA methyltransferase gene, dnmt3a and dnmt3x. Here we show, using phylogenetic analysis, that this gene duplication event occurred at least 150 million years ago, likely after the divergence of the lineage leading to the Aphidomorpha (phylloxerans, adelgids and true aphids) from that leading to the scale insects (Coccomorpha) and that the two paralogs are maintained in the genomes of all aphids examined. We also show that the mRNA of both dnmt3 paralogs is maternally expressed in the viviparous aphid ovary. During development both paralogs are expressed in the germ cells of embryos beginning at stage 5 and persisting throughout development. Treatment with 5‐azactyidine, a chemical that generally inhibits the DNA methylation machinery, leads to defects of oocytes and early‐stage embryos and causes a proportion of later stage embryos to be born dead or die soon after birth. These phenotypes suggest a role for DNA methyltransferases in reproduction, consistent with that seen in other insects. Taking the vast evolutionary history of the dnmt3 paralogs, and the localisation of their mRNAs in the ovary, we suggest there is a role for dnmt3a and/or dnmt3x in early development, and a role for DNA methylation machinery in reproduction and development of the viviparous pea aphid. [ABSTRACT FROM AUTHOR]

The American hoverfly Eupeodes americanus (Wiedemann) (Diptera: Syrphidae) is an aphidophagous predator during its larval stage and is currently being evaluated for inclusion in biocontrol programs as a new biocontrol agent. However, little is known about its reproductive aptitudes. The objective of the present study was to determine the reproductive parameters of E. americanus and to compare them with those of a commercialized and widely used biological control agent for aphids, the aphid midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). The preoviposition period, oviposition period, adult longevity, lifetime and daily fecundity, egg hatching rate, and fertility were determined for E. americanus females and compared to those of A. aphidimyza. Trials were conducted under laboratory conditions in rearing cages on the broad bean plant Vicia faba L. (Fabaceae), infested with pea aphids Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). The results revealed that the preoviposition period, oviposition period, and adult longevity were significantly longer in E. americanus than in A. aphidimyza. The daily fecundity and egg-hatching rate were similar in both species. However, lifetime fecundity and fertility were considerably higher in E. americanus than in A. aphidimyza. This study demonstrates that the reproductive capacity of E. americanus is clearly superior to that of A. aphidimyza and therefore supports its inclusion in the aphid pest management program as a new biocontrol agent. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is an economically important forage legume. As a result of the extensive and intensive cultivation of alfalfa planting and the gradual expansion of planting areas, pest occurrence has increased in frequency. Aphids are one of the main pests that threaten the growth and productivity of alfalfa. After an aphid outbreak, alfalfa yield and quality are commonly greatly reduced. At present, there are few studies on alfalfa plants infested with aphids, so it is imperative to study the regulatory mechanisms of aphid infestation tolerance in alfalfa. In this study, alfalfa plants from the variety "Wudi" were investigated, and pea aphids were selected for inoculation. The transcriptome and metabolome data were analyzed at three time points (0 d, 1 d, and 4 d), revealing 3458 differentially expressed genes and 358 differential metabolites. Trend analysis of DEGs and DAMs revealed that the former were significantly enriched in three distinct trends, whereas the latter were significantly enriched in only one. Moreover, 117 important hub genes associated with alfalfa response to aphid infestation were screened by WGCNA. By mapping DEGs and DAMs to KEGG pathways, it was found that the "phenylpropanoid biosynthesis", "flavonoid biosynthesis", and "isoflavonoid biosynthesis" pathways play an important role in alfalfa responses to aphid infestation. These results further elucidate the regulatory mechanism of alfalfa in response to aphid infestation and provide valuable information for breeding new aphid-resistant plant varieties. [ABSTRACT FROM AUTHOR]

Abstract The adaptability of insects to hosts has long been a focal point in the study of insect-plant interactions. The pea aphid (Acythosiphon pisum), a significant pest of numerous leguminous crops, not only inflicts direct economic losses but also disseminates various plant viruses. To understand how pea aphids adapt to diverse alfalfa varieties. We analyzed the differentially expressed genes (DEGs) of pea aphids in distinct alfalfa varieties using transcriptome sequencing, and subsequently conducted functional validation of these genes. Comparative analysis between pea aphids feeding on susceptible and resistant strains revealed that DEGs in aphids feeding on resistant strains were primarily associated with transcriptional enrichment in the sugar, amino acid, protein, and lipid metabolism pathways. Fourteen DEGs related to adaptation of the pea aphid to alfalfa were chosen, including five carboxylesterases (CarE), four cytochrome P450s, three glutathione S-transferases, and two peroxidases (POD). RT-qPCR results indicated significant up-regulation of two carboxylesterase genes and two peroxidase genes after 24 h of feeding resistant alfalfa (Gannong 5, GN5) compared to the susceptible varieties (Hunter River, LRH), particularly highlighting the high expression levels of ApCarE4 and ApPOD3. Simultaneously, RNAi-induced knockdown of ApCarE4 and ApPOD3 led to a higher mortality of pea aphids in the alfalfa Hunter River. These results indicate that ApPOD3 and ApCarE4 are involved in the detoxification of metabolic functions in the adaptation of pea aphids to host switching. These findings contribute to the understanding of pea aphid adaptation to host plants and lay a foundation for further exploration of the physiological roles of carboxylesterase and peroxidase genes in pea aphids.

This study identified and monitored the population fluctuations of insect vectors of Cowpea aphid-borne mosaic virus (CABMV) in experimental orchards in the North and Northwest Regions of the State of Paraná. The experiments were conducted in the cities of Londrina and Paranavaí at the Experimental Research Stations of the Instituto de Desenvolvimento Rural do Paraná-IAPAR-EMATER (IDR-Paraná), Brazil. The study period was from September 2019 to March 2021. In the experiments conducted in Londrina and in Paranavaí, yellow passion fruit plants were grown in trellis systems. Moericke traps were used to capture insects, and collections were performed weekly. Aphids were identified using a taxonomic identification key. The numbers of aphids present in each region were compared, and the populations were correlated with the climate and local precipitation. A total of 1522 and 1340 winged aphids were observed in the experiments in Londrina and Paranavaí, respectively. In Londrina, moderate positive correlations were observed between the number of insects and the maximum and average temperatures, while negative correlations were observed between the number of insects and the minimum temperature and precipitation. In contrast, in Paranavaí, the correlation between aphids and abiotic factors was negative, where maximum temperature was strongly correlated. In both regions, the following seven species of aphid vectors of CABMV were detected: Aphis fabae, Aphis gossypii, Toxoptera citricida, Acyrthosiphon pisum, Brevicoryne brassicae, Macrosiphum euphorbiae and Uroleucon ambrosiae. The population fluctuations of these species were influenced by variations in temperature and precipitation. [ABSTRACT FROM AUTHOR]

Sitobion avenae presents a major challenge, leading to significant reductions in wheat yield per year. This study aimed to explore the potential of targeting Voltage-gated Sodium Channels (VGSCs) in S. avenae through RNA interference (RNAi) as a means to combat this pest. Two-dimensional polyacrylamide gel electrophoresis differential expression resulted in the identification of peroxidase, Synaptotagmin, and VGSCs as RNAi targets in S. avenae. VGSCs gene was further selected as an RNAi target; essential transmembrane proteins crucial for nerve cell action potentials: and also, a commercial insecticide target. VGSCs were amplified by reverse transcriptase PCR, sequenced, and deposited in Gen Bank. The ID allotted was OR777606. ERNAi tool was utilized to generate 143 small interfering RNA sequences and one double-stranded RNA target. Phylogenetic analysis revealed evolutionary links between the VGSCs gene in S. avenae and related aphid species like Myzus persicae, Acyrthosiphon pisum, and Diuraphis noxia. Quantitative real-time PCR analysis revealed S. avenae mortality, decreased fecundity, and shortened lifespan; attributable to the down-regulation of VGSCs gene expression (35%), and mortality up to 61% among 3rd instar nymphs. Adult S. avenae exposed to dsVGSCs during their 3rd nymph stage exhibit reduced reproducibility and longevity (surviving less than 20 days). The findings suggest VGSCs as a promising RNAi target; having a potential for agricultural pest management. [ABSTRACT FROM AUTHOR]

Piercing-sucking insects are extremely efficient vectors of animal and plant pathogens. This group is polyphyletic with the piercing organ highly heterogenous in its structure and morphogenesis, adapted to a specific host and feeding mechanism. For instance, hemimetabolous aphids feed on plant sap from nymphs to adults and they renew their stylets at each molt, thanks to specialized secreting glands. Distinctly, holometabolous mosquitoes have two feeding modes: larvae feed in water by filtering and scraping surfaces with their mouths, while female adults can acquire blood from vertebrate hosts. The pupal metamorphosis allows switching from one feeding habit to another. Here, we present a deep characterization of the biogenesis of the adult mouthparts in parthenogenetic females of the pea aphid Acyrthosiphon pisum (Harris 1776) (Hemiptera: Aphididae) and in females of the mosquito Aedes albopictus (Skuse 1895) (Diptera: Culicidae), investigated using non-invasive X-ray synchrotron-based microtomography. Comparing datasets collected from aphid juvenile and adult stages and from preimaginal and adult stages of the mosquito, we were able to track the morphological changes of secreting glands and the synthesis of the adult stylet in aphid heads and to follow the de novo formation of mosquito mouthparts in pupae. Our study provides a baseline for investigating the evolution and the development of piercing-sucking mouthparts and to better understand how morphogenesis works in insects. [ABSTRACT FROM AUTHOR]

The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species that exhibits a remarkable annual life cycle, which is tightly coupled to the seasonal changes in day length. During spring and summer, characterised by longer days, aphid populations consist exclusively of viviparous females that reproduce parthenogenetically. When autumn comes and the days shorten, aphids switch their reproductive mode and generate males and oviparous sexual females, which mate and produce cold-resistant eggs that overwinter and survive the unfavourable season. While the photoperiodic responses have been well described, the nature of the timing mechanisms which underlie day length discrimination are still not completely understood. Experiments from the 1960's suggested that aphids rely on an 'hourglass' clock measuring the elapsed time during the dark night by accumulating a biochemical factor, which reaches a critical threshold at a certain night length and triggers the switch in reproduction mode. However, the photoperiodic responses of aphids can also be attributed to a strongly dampened circadian clock. Recent studies have uncovered the molecular components and the location of the circadian clock in the brain of the pea aphid and revealed that it is well connected to the neurohormonal system controlling aphid reproduction. We provide an overview of the putative mechanisms of photoperiodic control in aphids, from the photoreceptors involved in this process to the circadian clock and the neuroendocrine system. [ABSTRACT FROM AUTHOR]

Insects detect and discriminate a diverse array of chemicals using odorant receptors (ORs), which are ligand-gated ion channels comprising a divergent odorant-sensing OR and a conserved odorant receptor co-receptor (Orco). In this work, we report structures of the ApOR5-Orco heterocomplex from the pea aphid Acyrthosiphon pisum alone and bound to its known activating ligand, geranyl acetate. In these structures, three ApOrco subunits serve as scaffold components that cannot bind the ligand and remain relatively unchanged. Upon ligand binding, the pore-forming helix S7b of ApOR5 shifts outward from the central pore axis, causing an asymmetrical pore opening for ion influx. Our study provides insights into odorant recognition and channel gating of the OR-Orco heterocomplex and offers structural resources to support development of innovative insecticides and repellents for pest control. [ABSTRACT FROM AUTHOR]

Background: Natural products are important sources for the discovery of new biopesticides to control the worldwide destructive pests Acyrthosiphon pisum Harris. Here, insecticidal substances were discovered and characterized from the secondary metabolites of the bio-control microorganism Bacillus velezensis strain ZLP-101, as informed by whole-genome sequencing and analysis. Results: The genome was annotated, revealing the presence of four potentially novel gene clusters and eight known secondary metabolite synthetic gene clusters. Crude extracts, prepared through ammonium sulfate precipitation, were used to evaluate the effects of strain ZLP-101 on Acyrthosiphon pisum Harris aphid pests via exposure experiments. The half lethal concentration (LC50) of the crude extract from strain ZLP-101 against aphids was 411.535 mg/L. Preliminary exploration of the insecticidal mechanism revealed that the crude extract affected aphids to a greater extent through gastric poisoning than through contact. Further, the extracts affected enzymatic activities, causing holes to form in internal organs along with deformation, such that normal physiological activities could not be maintained, eventually leading to death. Isolation and purification of extracellular secondary metabolites were conducted in combination with mass spectrometry analysis to further identify the insecticidal components of the crude extracts. A total of 15 insecticidal active compounds were identified including iturins, fengycins, surfactins, and spergualins. Further insecticidal experimentation revealed that surfactin, iturin, and fengycin all exhibited certain aphidicidal activities, and the three exerted synergistic lethal effects. Conclusions: This study improved the available genomic resources for B. velezensis and serves as a foundation for comprehensive studies of the insecticidal mechanism by Bacillus velezensis ZLP-101 in addition to the active components within biological control strains. [ABSTRACT FROM AUTHOR]

The host immunosuppression by parasitic wasps is an important component of the host regulation strategy. The venom injected at the oviposition is one of the key‐factors involved in this host alteration and, in some parasitoids, its immunosuppressive role is complemented by wasp's symbionts. Most studies in this research area are related to hosts belonging to Lepidoptera and Diptera, for which a strong immune response is observed, whereas little is known for hemimetabolous host species, characterized by apparently much weaker defense barriers. To fill this research gap, here we focus on the host–parasitoid system Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) – Aphidius ervi Haliday (Hymenoptera: Braconidae). We functionally characterized a serine protease homolog (AeSPH) protein in vivo, identified in the venom of the aphid endoparasitoid A. ervi, generating AeSPH‐depleted female wasps by RNA interference and evaluating their capacity to successfully parasitize the host. Parasitism success rate was negatively affected by AeSPH knockdown and associated with an increased phenoloxidase (PO) cascade activation in aphids, scored by measuring PO enzymatic activity and the expression of phenoloxidase activating factor 2, a proPO‐activating gene upregulated in response to A. ervi parasitism. Our results indicate that AeSPH contributes to parasitism success by inhibiting the melanization response of the host, which is therefore an important component of the defense barriers involved in the parasitoid egg suppression. The ongoing studies on other virulence factors in A. ervi venom will allow to further characterize the immunosuppression strategy and its possible broader role in the host regulation through its action on aphid symbiont development. [ABSTRACT FROM AUTHOR]

One of the successful strategies developed for studying the gene function of aphids is to silence aphid gene expression by plant-mediated RNA interference (RNAi). In this study, we analyzed the expression patterns and the biological functions of genes related to chitin metabolism ApCht7 and ApCht10 by using gene-specific plant-mediated RNAi in the green pea aphid, Acyrthosiphon pisum (Ap). The RT-qPCR results demonstrated that the RNAi-mediated silencing of these ApChts suppressed the expression of most genes involved in the chitin degradation pathway, but enhanced the expressions of ApHK, ApGFAT, ApPGM and ApCHS, indicating that the RNAi of ApChts could affect the expression of genes related to chitin metabolism and regulate the chitin metabolism. Furthermore, it resulted in a decrease in aphid body weight of aphids, with mortality rates ranging from 3.3 to 26.1%. Abnormal phenotypes (e.g., molting defect and wrinkled integument) were observed in the treated nymphs, leading to early lethality. The aphid reproduction rate reduced by 27.9–40.5% at 120 h after RNAi of ApChts. The target genes ApCht7 and ApCht10 expression were also downregulated in the progeny nymphs born from the mothers exposed to dsRNA-plants with significantly lower body weights. The previously mentioned results suggest that the effects of RNAi ApCht7 and ApCht10 are heritable and passed down to offspring. Our study provides a foundation for the practical application of the plant-mediated RNAi of ApCht7 and ApCht10 as a powerful tools and methods for controlling field aphid outbreaks. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pollen is a common plant‐derived food source for predatory ladybird beetles under field conditions, yet the potential for pollen to improve the quality of artificial diets remains largely unexplored. In this study, we developed three pollen diets by incorporating varying proportions of canola bee pollen (7.5%, 15.0% and 22.5% with 2.5%, 5.0%, and 7.5% of water, respectively) into a conventional diet. The feeding efficiency of Harmonia axyridis, an omnivorous predator, was evaluated and compared on three pollen diets, a conventional nonpollen diet and pea aphids. RESULTS: The larvae fed a medium or high pollen diet exhibited significantly higher survival in the 4th instar, pupa and adult stages than those fed a nonpollen diet. These larvae also developed into significantly heavier adults, and their survival rates in adulthood were comparable to those fed pea aphids. Specifically, we revealed the underlying mechanisms through which a high pollen diet enhances pupal development. Consumption of high pollen diet versus nonpollen diet resulted not only in a significant decrease in pupal glycogen content, but also an increase in adult lipid content. Both diet treatments induced similar changes in carbohydrate and glycogen content compared to the aphid diet while exhibiting different alterations in pupal protein content and adult lipid content. Furthermore, the transcriptome analysis revealed that the nutrient metabolism, immune response, and cuticle development pathways were predominantly enriched among the differentially expressed genes (DEGs). CONCLUSION: Canola bee pollen offers diverse advantages in terms of rearing H. axyridis larvae with an artificial diet, which will advance the development of effective diets for predaceous coccinellids. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Hesperidin is a highly bioactive natural flavonoid whose role in ecological interactions is poorly known. In particular, the effects of hesperidin on herbivores are rarely reported. Flavonoids have been considered as prospective biopesticides; therefore, the aim of the present study was to examine the influence of hesperidin on the host plant selection behavior of three aphid (Hemiptera: Aphididae) species: Acyrthosiphon pisum Harrris, Rhopalosiphum padi (L.), and Myzus persicae (Sulz.). The aphid host plants were treated with 0.1% and 0.5% ethanolic solutions of hesperidin. Aphid probing behavior in the no-choice experiment was monitored using electropenetrography and aphid settling on plants in the choice experiment was recorded. The results demonstrated that hesperidin can be applied as a pre-ingestive, ingestive, and post-ingestive deterrent against A. pisum, as an ingestive deterrent against R. padi, and as a post-ingestive deterrent against M. persicae using the relatively low 0.1% concentration. While in A. pisum the deterrent effects of hesperidin were manifested as early as during aphid probing in peripheral plant tissues, in M. persicae, the avoidance of plants was probably the consequence of consuming the hesperidin-containing phloem sap. [ABSTRACT FROM AUTHOR]

In the Institute of Forage Crops, harmful and useful insects in spring forage pea were studied during 2020- 2022 in the Experimental Field. Species composition and population density of dominant insects were determined. The mowing with an entomological net was used. Pea weevil - Bruchus pisorum L.; Tychius quinquepunctatus L.; nodule weevils of genus Sitona; pea aphid - Acyrthosiphon pisum Harris and tobacco thrips - Thrips tabaci L. were dominant harmful species of economic importance. Coccinella septempunctata L. and Aeolothrips intermedius Bagn. were the most commonly met and effective among the entomophagous. [ABSTRACT FROM AUTHOR]

Simple Summary: The pea aphid, Acyrthosiphon pisum, is a serious pest of legume crops that can produce winged and wingless offspring in response to the environmental conditions. We found that, under crowded conditions, the red morph A. pisum produced more winged offspring than the green morph. The signaling pathways involved in aphid wing determination also play important roles in regulating growth, development, and metabolism. Thus, we examined the association between the wing-producing ability and the growth rate, development time, reproductive capacity, and energy metabolism in these two color morphs. The growth rate, levels of glycogen and triglycerides in red morphs were significantly higher than those of green morphs, whereas green morphs produced more offspring. Red morphs also consumed more triglycerides during starvation and had stronger starvation tolerance. Furthermore, the expression levels of genes involved in the insulin pathway, glycolysis, and lipolysis in red aphids were also higher. These results suggest that the wing-producing ability of the pea aphid may be associated with its growth and metabolism. The pea aphid, Acyrthosiphon pisum, is a major pest of legume crops, exhibiting distinct polymorphism in terms of wings and body color. We found that, under crowded conditions, the red morph A. pisum produced more winged offspring than the green morph. The signaling pathways involved in aphid wing determination, like insulin and ecdysone, also play important roles in regulating growth, development, and metabolism. Thus, here, we examined the association between the wing-producing ability and the growth rate, development time, reproductive capacity, and energy metabolism in these two color morphs. The growth rate of red morphs was significantly higher than that of green morphs, whereas green morphs produced more offspring during the first 6 days of the adult stage. Red morphs accumulated higher levels of glycogen and triglycerides and consumed more triglycerides during starvation; however, green aphids consumed more trehalose during food deprivation. Red aphids exhibited stronger starvation tolerance, possibly due to their higher triglyceride catabolic activity. Furthermore, the expression levels of genes involved in the insulin pathway, glycolysis, and lipolysis in red aphids were higher than those in green aphids. These results suggest that the wing-producing ability of the pea aphid may be associated with its growth and metabolism, which may be due to the shared regulatory signaling pathways. [ABSTRACT FROM AUTHOR]

Simple Summary: Acetamiprid, commonly used in agriculture to control aphids, faces the problem of resistance development in certain aphid species. To investigate the insect mechanisms involved in the adaptation process to acetamiprid, we compared the gene expression and microbial profiles of a pea aphid strain selected with acetamiprid (RS) with those of a non-selected strain (SS) using advanced omics techniques. The overall analysis revealed significant changes in the expression of genes involved in carbon and fatty acid metabolism in RS compared to those of SS aphids. In particular, we found increased expression of specific genes related to the synthesis of the components of the epidermal wax layer, suggesting that adaptation to acetamiprid involves the synthesis of a thicker protective layer. Additionally, subtle shifts in the bacterial composition of RS were detected. These results contribute valuable insights into the mechanisms underlying the pea aphid's response to acetamiprid exposure. Such understanding is essential for informing future research efforts and developing more effective strategies to control this pest. Acetamiprid is a broad-spectrum neonicotinoid insecticide used in agriculture to control aphids. While recent studies have documented resistance to acetamiprid in several aphid species, the underlying mechanisms are still not fully understood. In this study, we analyzed the transcriptome and metatranscriptome of a laboratory strain of the pea aphid, Acyrthosiphon pisum (Harris, 1776), with reduced susceptibility to acetamiprid after nine generations of exposure to identify candidate genes and the microbiome involved in the adaptation process. Sequencing of the transcriptome of both selected (RS) and non-selected (SS) strains allowed the identification of 14,858 genes and 4938 new transcripts. Most of the differentially expressed genes were associated with catalytic activities and metabolic pathways involving carbon and fatty acids. Specifically, alcohol-forming fatty acyl-CoA reductase (FAR) and acyl-CoA synthetase (ACSF2), both involved in the synthesis of epidermal wax layer components, were significantly upregulated in RS, suggesting that adaptation to acetamiprid involves the synthesis of a thicker protective layer. Metatranscriptomic analyses revealed subtle shifts in the microbiome of RS. These results contribute to a deeper understanding of acetamiprid adaptation by the pea aphid and provide new insights for aphid control strategies. [ABSTRACT FROM AUTHOR]

When ecological and evolutionary dynamics occur on comparable timescales, persistence of the ensuing eco-evolutionary dynamics requires both ecological and evolutionary stability. This unites key questions in ecology and evolution: How do species coexist, and what maintains genetic variation in a population? In this work, we investigated a host-parasitoid system in which pea aphid hosts rapidly evolve resistance to Aphidius ervi parasitoids. Field data and mathematical simulations showed that heterogeneity in parasitoid dispersal can generate variation in parasitism-mediated selection on hosts through time and space. Experiments showed how evolutionary trade-offs plus moderate host dispersal across this selection mosaic cause host-parasitoid coexistence and maintenance of genetic variation in host resistance. Our results show how dispersal can stabilize both the ecological and evolutionary components of eco-evolutionary dynamics. [ABSTRACT FROM AUTHOR]

Simple Summary: This study explores the mechanisms affecting offspring sex ratios in the pea aphid, Acyrthosiphon pisum (Harris), a key issue in evolutionary ecology. It tests the impacts of the presence of both the same and different clones, as well as juvenile hormone III (JH III) levels, on offspring sex allocation. Using red and green clones and the agar method, this study set up three initial treatments using sexuparae and tracked daily offspring number and sex. In a mixed-clone treatment, 1 sexupara of the green clone and 20 oviparous females of either red (1G + 20Rov) or green (1G + 20Gov) clone were transferred onto agar leaves, with a control (1G) established for comparison. After the production of sexuparae, JH III doses were applied to them, and hormone titers and sex allocation in offspring were meticulously measured. The results highlighted marked variations in sex allocation, especially an increase in ovipara number in mixed-clone treatment groups. JH III application reversed this effect, indicating that mixed-clone treatment leads to lowered JH titers, which in turn affects sex allocation. This study concludes that A. pisum sexuparae can modify offspring sex allocation in response to adjacent clones, showing diverse mechanisms of sex allocation, where JH III plays a critical role. The mechanism controlling sex allocation in the pea aphid, Acyrthosiphon pisum (Harris), remains a crucial yet unresolved issue in the field of evolutionary ecology. This study aims to assess the influence of the presence of both self and non-self clones, along with juvenile hormone III (JH III) titer, on the sex allocation of aphid offspring. To this end, red and green clones were utilized as experimental subjects, and the agar method was employed. Initially, three distinct experimental treatments were established using sexuparae, and the daily offspring count and sex allocation in each treatment zone were recorded. Subsequently, an additional experimental condition involving mixed-clone treatments was introduced. This procedure entailed the transfer of a single sexupara and 20 oviparous females from either the red (1G + 20Rov) or green clone (1G + 20Gov) onto a leaf on agar medium. Simultaneously, a control setup with a new sexupara (1G) was established. Three days following sexupara production, a dose of 0, 25, or 50 ng of JH III was applied to the aphids' abdomens. Subsequently, the titers of JH III in the sexuparae across each treatment group were quantified, and the extent of sex allocation was tallied. The findings demonstrated pronounced disparities in sex allocation among the various treatments and, notably, a substantial increase in the total offspring and oviparous number in the mixed-clone treatment group. The effects of mixed-clone treatment on the sex allocation patterns of the sexupara progeny could be determined by the application of exogenous JH III, indicating that JH may mediate the effects of mixed-clone treatment on sex allocation. Consequently, it can be concluded that A. pisum sexuparae possess the capability to modulate their sex allocation in response to the nature of adjacent competitor clones, thereby demonstrating a variety of sex allocation patterns. Throughout this process, JH III plays a pivotal role. [ABSTRACT FROM AUTHOR]

Soil rhizobia promote nitrogen fixation in legume hosts, maximizing their tolerance to different biotic stressors, plant biomass, crop growth, and yield. While the presence of soil rhizobia is considered beneficial for plants, few studies have assessed whether variation in rhizobia abundance affects the tolerance of legumes to stressors. To address this, we assessed the effects of variable soil rhizobia inoculum concentrations on interactions between a legume host (Pisum sativum), a vector insect (Acyrthosiphon pisum), and a virus (Pea enation mosaic virus, PEMV). We showed that increased rhizobia abundance reduces the inhibitory effects of PEMV on the nodule formation and root growth in 2-week-old plants. However, these trends were reversed in 4-week-old plants. Rhizobia abundance did not affect shoot growth or virus prevalence in 2- or 4-week-old plants. Our results show that rhizobia abundance may indirectly affect legume tolerance to a virus, but effects varied based on plant age. To assess the mechanisms that mediated interactions between rhizobia, plants, aphids, and PEMV, we measured the relative expression of gene transcripts related to plant defense signaling. Rhizobia concentrations did not strongly affect the expression of defense genes associated with phytohormone signaling. Our study shows that an abundance of soil rhizobia may impact a plant's ability to tolerate stressors such as vector-borne pathogens, as well as aid in developing sustainable pest and pathogen management systems for legume crops. More broadly, understanding how variable rhizobia concentrations can optimize legume-rhizobia symbiosis may enhance the productivity of legume crops. [ABSTRACT FROM AUTHOR]

BACKGROUND: The push–pull strategy is considered as a promising eco‐friendly method for pest management. Plant volatile organic compounds (PVOCs) act as semiochemicals constitute the key factor in implementing this strategy. Benzyl alcohol and geraniol, as functional PVOCs, were reported to regulate insect behavior, showing the potential application in pest control. Using geraniol as lead, a geraniol derivative 5i with fine repellent activity was discovered in our previous work. In order to explore novel, eco‐friendly aphid control agents, a series of benzyl geranate derivatives was designed and synthesized using 5i as the lead and benzyl alcohol as the active fragment. RESULTS: Benzyl alcohol was firstly evaluated to have repellent activity to Acyrthosiphon pisum. Based on this repellent fragment, a series of novel benzyl geranate derivatives was rationally designed and synthesized using a scaffold‐hopping strategy. Among them, compound T9, with a binding affinity (Kd = 0.43 μm) and a substantial repellency of 64.7% against A. pisum, is the most promising compound. Molecule docking showed that hydrophobic and hydrogen‐bonding interactions substantially influenced the binding affinity of compounds with ApisOBP9. Additionally, T9 exhibited low‐toxicity to honeybees and ladybugs. CONCLUSION: Using a simple scaffold‐hopping strategy combined with active fragment benzyl alcohol, a new derivative T9, with high aphid‐repellency and low‐toxicity to nontarget organisms, can be considered as a novel potential eco‐friendly aphid control agent for sustainable agriculture. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The global threat of invasive alien species (IAS) being introduced into new habitats is concerning, particularly in agricultural crops as invasive insect species are continuing to expand their distribution through anthropogenic activities and climate changes. Pea aphids (Acyrthosiphon pisum Harris) are an economic threat to numerous legume crops as they can reproduce parthenogenetically, damage crops directly, and vector over 30 plant viruses as the insect's distribution continues to spread. There are no existing pea aphid-specific risk maps that identify the habitat suitability of pea aphids at either a regional or global scale. Here, we used Species Distribution Models (SDMs) to evaluate which climatic variables influence pea aphid distribution, identify regions of potential distribution, and analyze the global distribution of pea aphids under current and future climate change scenarios (SSP 126, 245, and 370) by utilizing presence-only SDMs based on Maximum Entropy (MaxEnt). The modeling results indicate suitable conditions are relevant for pea aphid establishment in six out of seven continents, with significant range expansion in western Canada, the United States of America, and across Europe. We identified human influence to be the most prominent predictor in determining the distribution of pea aphids, supporting the fact that invasive species distributions are heavily impacted by human activities.

Global change drivers are imposing novel conditions on Earth's ecosystems at an unprecedented rate. Among them, biological invasions and climate change are of critical concern. It is generally thought that strictly asexual populations will be more susceptible to rapid environmental alterations due to their lack of genetic variability and, thus, of adaptive responses. In this study, we evaluated the persistence of a widely distributed asexual lineage of the alfalfa race of the pea aphid, Acyrthosiphon pisum, along a latitudinal transect of approximately 600 km in central Chile after facing environmental change for a decade. Based on microsatellite markers, we found an almost total replacement of the original aphid superclone by a new variant. Considering the unprecedented warming that this region has experienced in recent years, we experimentally evaluated the reproductive performance of these two A. pisum lineages at different thermal regimes. The new variant exhibits higher rates of population increase at warmer temperatures, and computer simulations employing a representative temperature dataset suggest that it might competitively displace the original superclone. These results support the idea of a superclone turnover mediated by differential reproductive performance under changing temperatures. [ABSTRACT FROM AUTHOR]

One of the major insect pests in Pisum sativum L. (is Acyrthosiphon pisum Harris (Hemiptera: pests in Pisum sativum L. (Hemiptera: Aphididae) is Acyrthosiphon pisum Harris (Hemiptera: Aphididae). An effective strategy for aphid control is the resistant host plant use. The current study aimed to identify resistance mechanisms and assess biochemical and morphological markers of pea aphid resistance in pea accessions. Meteorological variables affected the pea aphid density, which positively correlated with temperature, while precipitation amount and humidity negatively impacted. The aphid number was significantly and positively associated with the leaf area and the nitrogen content but negatively correlated with calcium and phosphorus levels. The pea aphid-resistant cultivars L 123-7-11, L 128-1and L 125-5 had small leaf areas, and high phosphorus and calcium content but a low nitrogen level. In the mutual influence of the plant indicators, phosphorus concentration had the highest negative impact on pea aphid density, followed by calcium. The plant marker inclusion in the pea breeding process is an efficient tool for a substantial selection program improvement for aphid resistance. Therefore, resistant host plants are essential tools promoting considerable selection program improvement for aphid resistance in the P. sativum breeding process and helping develop sustainable and environmentally friendly agriculture. [ABSTRACT FROM AUTHOR]

BACKGROUND: In recent years, the use of the RNA interference technology (RNAi) has emerged as one of the new strategies for species‐specific control of insect pests. Its specificity depends on the distinctiveness of the target gene sequence for a given species. In this work, we assessed in the pea aphid Acyrthosiphon pisum (A. pisum) the use of a double‐stranded RNA (dsRNA) that targets the β2 divergent nicotinic acetylcholine receptor (nAChR) subunit (dsRNA‐β2), which shares low sequence identity with other subunits, to control populations of this pest at different developmental stages. Because nAChRs are targeted by neonicotinoid insecticides such as imidacloprid, we also assessed the effect of dsRNA‐β2 coupled to this insecticide on aphid survival. Finally, because the effect of a control agent on beneficial insect must be considered before any use of new pest management strategies, the acute toxicity of dsRNA‐β2 combined with imidacloprid was evaluated on honeybee Apis mellifera. RESULTS: In this work, we demonstrated that dsRNA‐β2 alone has an insecticidal effect on aphid larvae and adults. Moreover, dsRNA‐β2 and imidacloprid effects on aphid larvae and adults were additive, meaning that dsRNA‐β2 did not alter the efficacy of imidacloprid on these two developmental stages. Also, no obvious acute toxicity on Apis mellifera was reported. CONCLUSION: Using RNAi that targets β2 divergent nAChR subunit is effective alone or combined with imidacloprid to control A. pisum at larval and adult stages. Because no obvious Apis mellifera mortality has been reported, this RNAi‐based pest management strategy should be considered to control insect pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Symbiotic microbes have evolved to become an important source of phenotypic plasticity in host insects. In aphids, facultative endosymbionts have been found capable of influencing host phenotypes, such as against natural enemies and host fitness. However, the related evidence has been mainly gathered from a few model organisms, such as the pea aphid. Here, we explored the roles of a common facultative symbiont of the genus Rickettsia in the grain aphid Sitobion avenae. We first observed that Rickettsia-infected aphids (either natural or artificial status) benefit of a higher population increase rate (nearly 1.23-fold) than the Rickettsia-free aphids from the same genetic background. While Rickettsia presence did not confer resistance against the aphid parasitoid Aphidius gifuensis, emerged wasps from Rickettsia-infected aphids had a significantly reduced weight and their sex ratio was biased toward more female wasps. These results suggest that the presence of the symbiont ameliorates the fitness of its aphid host, but impacts the growth of parasitoid offspring and the parasitoid sex-ratio in a way that could be detrimental for the aphid. This demonstrates that the presence of a facultative symbiont may lead to both positive and negative trade-offs, which may ultimately not affect the fitness of the host population as they are compensatory. [ABSTRACT FROM AUTHOR]

Simple Summary: Pea aphids (Acyrthosiphon pisum) serve as a model insect for ecological research and have recently emerged as a significant pest of alfalfa. Amino acid uptake and balance in insects typically rely on amino acid transporters. In this investigation, RT-qPCR was employed to examine the distinct gene expression patterns of seven amino acid transporters subsequent to pea aphid feeding on resistant and susceptible alfalfa varieties. RNA interference targeting the pea aphid ACYPI000536 and ACYPI004320 genes was carried out via a plant-mediated approach, elucidating the preliminary functions of these genes. The study revealed that down-regulating the ACYPI000536 gene led to increased histidine and lysine levels in pea aphids, subsequently elevating mortality post-feeding on the susceptible alfalfa variety "Lie Renhe". Conversely, down-regulating the ACYPI004320 gene resulted in elevated phenylalanine levels in pea aphids, leading to reduced mortality following feeding on the highly resistant alfalfa variety "Gannong 5". In recent years, pea aphids have become major pests of alfalfa. Our previous study found that "Gannong 5" is a highly aphid-resistant alfalfa variety and that "Lie Renhe" is a susceptible one. The average field susceptibility index of "Gannong 5" was 31.31, and the average field susceptibility index of "Lie Renhe" was 80.34. The uptake and balance of amino acids in insects are usually dependent on amino acid transporters. RT-qPCR was used to detect the relative expression levels of seven amino acid transporter differential genes in the different instar pea aphids fed on resistant and susceptible alfalfa varieties after 24 h, and two key genes were selected. When pea aphids fed on "Gannong 5", the expression of ACYPI004320 was significantly higher than that in pea aphids fed on "Lie Renhe"; however, the expression of ACYPI000536 was significantly lower than that in pea aphids fed on "Lie Renhe". Afterward, the RNA interference with pea aphid ACYPI000536 and ACYPI004320 genes was performed using a plant-mediated method, and gene function was verified via liquid chromatography–mass spectrometry and pea aphid sensitivity to aphid-resistant and susceptible alfalfa varieties. The results showed that the down-regulation of the ACYPI000536 gene expression led to an increase in the histidine and lysine contents in pea aphids, which, in turn, led to an increase in mortality when pea aphids fed on the susceptible variety "Lie Renhe". The down-regulation of the ACYPI004320 gene expression led to an increase in phenylalanine content in pea aphids, which, in turn, led to a decrease in mortality when pea aphids fed on the resistant variety "Gannong 5". [ABSTRACT FROM AUTHOR]

Introduction: The pea aphid, Acyrthosiphon pisum, is a typical sap-feeding insect and an important worldwide pest. There is a primary symbiont-Buchnera aphidicola, which can synthesize and provide some essential nutrients for its host. At the same time, the hosts also can actively adjust the density of bacterial symbiosis to cope with the changes in environmental and physiological factors. However, it is still unclear how symbionts mediate the interaction between herbivorous insects' nutrient metabolism and host plants. Methods: The current study has studied the effects of different host plants on the biological characteristics, Buchnera titer, and nutritional metabolismof pea aphids. This study investigated the influence of different host plants on biological characteristics, Buchnera titer, and nutritional metabolism of pea aphids. Results and discussion: The titer of Buchnera was significantly higher on T. Pretense and M. officinalis, and the relative expression levels were 1.966±0.104 and 1.621±0.167, respectively. The content of soluble sugar (53.46±1.97µg/mg), glycogen (1.12±0.07µg/mg) and total energy (1341.51±39.37µg/mg) of the pea aphid on V. faba were significantly higher and showed high fecundity (143.86 ±11.31) and weight (10.46±0.77µg/mg). The content of total lipids was higher on P. sativum and T. pretense, which were 2.82±0.03µg/mg and 2.92±0.07µg/mg, respectively. Correlation analysis found that the difference in Buchnera titer was positively correlated with the protein content in M. officinalis and the content of total energy in T. pratense (P < 0.05). This study confirmed that host plants not only affected the biological characteristics and nutritional metabolism of pea aphids but also regulated the symbiotic density, thus interfering with the nutritional function of Buchnera. The results can provide a theoretical basis for further studies on the influence of different host plants on the development of pea aphids and other insects. [ABSTRACT FROM AUTHOR]

Heritable, facultative symbionts are common in arthropods, often functioning in host defence. Despite moderately reduced genomes, facultative symbionts retain evolutionary potential through mobile genetic elements (MGEs). MGEs form the primary basis of strain‐level variation in genome content and architecture, and often correlate with variability in symbiont‐mediated phenotypes. In pea aphids (Acyrthosiphon pisum), strain‐level variation in the type of toxin‐encoding bacteriophages (APSEs) carried by the bacterium Hamiltonella defensa correlates with strength of defence against parasitoids. However, co‐inheritance creates difficulties for partitioning their relative contributions to aphid defence. Here we identified isolates of H. defensa that were nearly identical except for APSE type. When holding H. defensa genotype constant, protection levels corresponded to APSE virulence module type. Results further indicated that APSEs move repeatedly within some H. defensa clades providing a mechanism for rapid evolution in anti‐parasitoid defences. Strain variation in H. defensa also correlates with the presence of a second symbiont Fukatsuia symbiotica. Predictions that nutritional interactions structured this coinfection were not supported by comparative genomics, but bacteriocin‐containing plasmids unique to co‐infecting strains may contribute to their common pairing. In conclusion, strain diversity, and joint capacities for horizontal transfer of MGEs and symbionts, are emergent players in the rapid evolution of arthropods. [ABSTRACT FROM AUTHOR]

Most insects harbour influential, yet non‐essential heritable microbes in their hemocoel. Communities of these symbionts exhibit low diversity. But their frequent multi‐species nature raises intriguing questions on roles for symbiont–symbiont synergies in host adaptation, and on the stability of the symbiont communities, themselves. In this study, we build on knowledge of species‐defined symbiont community structure across US populations of the pea aphid, Acyrthosiphon pisum. Through extensive symbiont genotyping, we show that pea aphids' microbiomes can be more precisely defined at the symbiont strain level, with strain variability shaping five out of nine previously reported co‐infection trends. Field data provide a mixture of evidence for synergistic fitness effects and symbiont hitchhiking, revealing causes and consequences of these co‐infection trends. To test whether within‐host metabolic interactions predict common versus rare strain‐defined communities, we leveraged the high relatedness of our dominant, community‐defined symbiont strains vs. 12 pea aphid‐derived Gammaproteobacteria with sequenced genomes. Genomic inference, using metabolic complementarity indices, revealed high potential for cooperation among one pair of symbionts—Serratia symbiotica and Rickettsiella viridis. Applying the expansion network algorithm, through additional use of pea aphid and obligate Buchnera symbiont genomes, Serratia and Rickettsiella emerged as the only symbiont community requiring both parties to expand holobiont metabolism. Through their joint expansion of the biotin biosynthesis pathway, these symbionts may span missing gaps, creating a multi‐party mutualism within their nutrient‐limited, phloem‐feeding hosts. Recent, complementary gene inactivation, within the biotin pathways of Serratia and Rickettsiella, raises further questions on the origins of mutualisms and host–symbiont interdependencies. [ABSTRACT FROM AUTHOR]

Objective: The principal delivery method for CRISPR-based genome editing in insects is now based on microinjection into single cells or embryos. The direct protein transduction systems cannot be employed in aphids because oogenesis occurs without apparent vitellogenesis. Given the limited timing of injection into the embryonic stage in oviparous aphids, a protein delivery system from the hemolymph to the germline and embryos would be a useful tool for genome editing. This study reports a newly developed direct protein delivery system for aphids using cell-penetrating peptides (CPPs). CPPs are short peptides that translocate across the plasma membrane when bound to cargo proteins. Results: Penetratin (PEN), a widely conserved CPP among insects, was identified in this study. We used mVenus, a recombinant fluorescent protein, as a visual marker for CPP availability assessments, and fused it with PEN by bacterial protein expression. The mVenus-PEN recombinant proteins were introduced into the hemolymph of adult unwinged Acyrthosiphon pisum females using a nanoinjector. Fluorescence emitted by mVenus-PEN was observed in various tissues, such as the gut, trachea, bacteriocytes, and their progeny. This study shows that PEN can deliver exogenously expressed proteins into tissues in vivo, indicating that CPPs are powerful tools for protein transduction. [ABSTRACT FROM AUTHOR]

In agroecosystems, plants frequently confront multiple biotic stressors, including herbivores and pathogens. The nature of these interactions plays a crucial role in mediating the activation of plant defense mechanisms. However, induction of plant chemical defenses has been more well studied than the induction of physical defenses. Here, we assessed the physical and chemical defense responses of pea (Pisum sativum) plants after exposure to three stressors: a vector herbivore (pea aphid, Acrythosiphon pisum), a non-vector herbivore (pea leaf weevil, Sitona lineatus), and a virus (Pea enation mosaic virus, PEMV). We used various histochemical staining techniques show that viruliferous A. pisum (transmitting PEMV) strongly induced callose deposition (aniline blue staining) and antioxidant-mediated defenses (DAB and NBT staining) in peas, primarily through accumulating reactive oxygen species (ROS). High-throughput phenotyping showed that viruliferous aphids reduced plant photosynthetic efficiency, but plants infected with PEMV had increased cell death (trypan blue staining). However, herbivory by aphids and weevils did not strongly induce defenses in peas, even though weevil feeding significantly reduced pea leaf area. These results show that not all herbivores induce strong defensive responses, and plant responses to vector species depends on their virus infection status. More broadly, our results indicate that variable stressors differentially regulate various plant responses through intricate chemical and physical defense pathways. [ABSTRACT FROM AUTHOR]

Organisms across the tree of life colonize novel environments by partnering with bacterial symbionts. These symbioses are characterized by intimate integration of host/ endosymbiont biology at multiple levels, including metabolically. Metabolic integration is particularly important for sap-feeding insects and their symbionts, which supplement nutritionally unbalanced host diets. Many studies reveal parallel evolution of host/endosymbiont metabolic complementarity in amino acid biosynthesis, raising questions about how amino acid metabolism is regulated, how regulatory mechanisms evolve, and the extent to which similar mechanisms evolve in different systems. In the aphid/Buchnera symbiosis, the transporter ApGLNT1 (Acyrthosiphon pisum glutamine transporter 1) supplies glutamine, an amino donor in transamination reactions, to bacteriocytes (where Buchnera reside) and is competitively inhibited by Buchnera-supplied arginine—consistent with a role regulating amino acid metabolism given host demand for Buchnera-produced amino acids. We examined how ApGLNT1 evolved a regulatory role by functionally characterizing orthologs in insects with and without endosymbionts. ApGLNT1 orthologs are functionally similar, and orthology searches coupled with homology modeling revealed that GLNT1 is ancient and structurally conserved across insects. Our results indicate that the ApGLNT1 symbiotic regulatory role is derived from its ancestral role and, in aphids, is likely facilitated by loss of arginine biosynthesis through the urea cycle. Given consistent loss of host arginine biosynthesis and retention of endosymbiont arginine supply, we hypothesize that GLNT1 is a general mechanism regulating amino acid metabolism in sap-feeding insects. This work fills a gap, highlighting the broad importance of co-option of ancestral proteins to novel contexts in the evolution of host/symbiont systems. [ABSTRACT FROM AUTHOR]

Climatic changes, such as heatwaves, pose unprecedented challenges for insects, as escalated temperatures above the thermal optimum alter insect reproductive strategies and energy metabolism. While thermal stress responses have been reported in different insect species, thermo-induced developmental abnormalities in phloem-feeding pests are largely unknown. In this laboratory study, we raised two groups of first instar nymphs belonging to two clones of the pea aphid Acyrthosiphon pisum, on fava beans Vicia faba. The instars developed and then asexually reproduced under constant exposure to a sub-lethal heatwave (27°C) for 14 days. Most mothers survived but their progenies showed abnormalities, as stillbirths and appendageless or weak nymphs with folded appendages were delivered. Clone N116 produced more deceased and appendageless embryos, contrary to N127, which produced fewer dead and more malformed premature embryos. Interestingly, the expression of the HSP70 and HSP83 genes differed in mothers between the clones. Moreover, noticeable changes in metabolism, e.g., lipids, were also detected and that differed in response to stress. Deformed offspring production after heat exposure may be due to heat injury and differential HSP gene expression, but may also be indicative of a conflict between maternal and offspring fitness. Reproductive altruism might have occurred to ensure some of the genetically identical daughters survive. This is because maintaining homeostasis and complete embryogenesis could not be simultaneously fulfilled due to the high costs of stress. Our findings shine new light on pea aphid responses to heatwaves and merit further examination across different lineages and species. [ABSTRACT FROM AUTHOR]

Systemic RNA interference deficient‐1‐like (SIL1) is considered a core component in dsRNA uptake in some insect species. Investigation related to the potential function of SIL1 in dsRNA uptake can contribute to a further understanding of RNA interference (RNAi) mechanisms in insects and agricultural pest control. However, the role of SIL1 in dsRNA uptake in insects such as aphids remains controversial. We have thoroughly analyzed the role of SIL1 from the model aphid Acyrthosiphon pisum (ApSIL1) in cellular dsRNA to clarify its function. First, the induced expression of ApSIL1 upon dsRNA oral exposure provided a vital clue for the possible involvement of ApSIL1 in cellular dsRNA uptake. Subsequent in vivo experiments using the RNAi‐of‐RNAi approach for ApSIL1 supported our hypothesis that the silencing efficiencies of reporter genes were reduced after inhibition of ApSIL1 expression. The impaired biological phenotypes of aphids, including cumulative average offspring, deformities of the nymph, and mortality upon pathogen infection, were then observed in the treatment group. Thereafter, in vitro dual‐luciferase reporter assay showed compelling evidence that the luciferin signal was significantly attenuated when dsluciferase or dsGFP was transferred into ApSIL1‐transfected Drosophila S2 cells. These observations further confirmed that the signal of Cy3‐labeled dsRNA was rapidly attenuated with time in ApSIL1‐transfected Drosophila S2 cells. Overall, these findings conclusively establish that ApSIL1 is involved in dsRNA uptake in A. pisum. [ABSTRACT FROM AUTHOR]

The first winged insects evolved from a wingless ancestor, but details of the transition to a fully-winged morphology remain unclear. Studying extant pterygotes with partial wings, such as the stick insects (order Phasmatodea), may help us to understand such a transition. Here, we address how a series of flight-related morphological parameters may correlate with flight evolution by studying different phasmids representing a volancy continuum ranging from miniaturized to full-sized wings. Variation in phasmid wing shape, venation, wing mass and the mass of flight muscle can be described by specific scaling laws referenced to wing length and wing loading. Also, the mass distribution of the body-leg system is conserved in spite of a wide range of variation in body shape. With reduced wing size and increased wing loading, the longitudinal position of the wing-bearing thoracic segments is shifted closer to the insects' centre of body mass. These results demonstrate complex reconfiguration of the flight system during wing morphological transitions in phasmids, with various anatomical features potentially correlated with reduced flight performance attained with partial wings. Although these data represent phasmid-specific features of the flight apparatus and body plan, the associated scaling relationships can provide insight into the functionality of intermediate conditions between wingless and fully-winged insects more generally. [ABSTRACT FROM AUTHOR]

There is increasing interest in the use of endosymbionts in pest control, which will benefit from the identification of endosymbionts from potential donor species for transfer to pest species. Here, we screened for endosymbionts in 123 Australian aphid samples across 32 species using 16S DNA metabarcoding. We then developed a qPCR method to validate the metabarcoding data set and to monitor endosymbiont persistence in aphid cultures. Pea aphids (Acyrthosiphon pisum) were frequently coinfected with Rickettsiella and Serratia, and glasshouse potato aphids (Aulacorthum solani) were coinfected with Regiella and Spiroplasma; other secondary endosymbionts detected in samples occurred by themselves. Hamiltonella, Rickettsia and Wolbachia were restricted to a single aphid species, whereas Regiella was found in multiple species. Rickettsiella, Hamiltonella and Serratia were stably maintained in laboratory cultures, although others were lost rapidly. The overall incidence of secondary endosymbionts in Australian samples tended to be lower than recorded from aphids overseas. These results indicate that aphid endosymbionts probably exhibit different levels of infectivity and vertical transmission efficiency across hosts, which may contribute to natural infection patterns. The rapid loss of some endosymbionts in cultures raises questions about factors that maintain them under field conditions, while endosymbionts that persisted in laboratory culture provide candidates for interspecific transfers. [ABSTRACT FROM AUTHOR]

This study was conducted to determine distribution pattern and related parameters of spotted alfalfa aphid, Therioaphis maculata (Buckten), pea aphid, Acyrthosiphon pisum (Harris) and two coccinellid species (Coccinella septempunctata L. and Hippodamia variegata Goeze) in six alfalfa fields during two growing seasons, 2016 and 2017. Weekly sampling was started when alfalfa plants reached 10 cm in height and continued until harvest. Each field was divided into 20m×20m plots. Two samples per plot per sampling time were randomly taken using a 1 × 1 m quadrat, to count adult coccinellids. Twenty alfalfa stems (longer than 10cm) per plot were randomly cut and shaken eight times on a white pan to record the aphids' density. The aphids that fell into the pan were counted and recorded. The ratio of variance to mean, as well as Taylor’s power law (TPL) and Iwao’s patchiness index (IPI), were used to determine the spatial distribution patterns of the insects. The variance exceeded the mean on all sampling dates, which may imply an aggregative distribution. Aggregation was also confirmed by using regression coefficient of both TPL (parameter b) and coefficient of IPI (β), which both were significantly above unity. Correlation between aphid counts and those of the coccinellids indicated that there was a positive but weak relationship between predator and prey densities in the fields, although a weak correlation may imply that factors other than prey accessibility contribute to the spatial distribution of the predators. Using different statistical methods provides useful information about the spatial distribution and dispersal pattern of aphids and natural enemies in alfalfa fields, and this information can be used in the biological control of pests. [ABSTRACT FROM AUTHOR]

Many species of insects show phenotypically plastic dispersal traits in response to suboptimal environmental conditions. These polyphenetic traits can have large impacts on the population dynamics of the dispersing insects. Therefore, it is important to understand what environmental factors affect the development of dispersal traits and how these factors affect population dynamics via immigration/emigration.Pea aphids (Acyrthosiphon pisum) exhibit a polyphenetic wing dimorphism in which individuals are either winged (alate) or not (apterous). The production of alate offspring is determined by environmental cues experienced by the mother. Environmental factors associated with these cues have been intensively studied, with crowding, host plant quality, natural enemies, fungal infection, and viral infection being shown to affect the production of pea aphid alates under controlled laboratory conditions. Nonetheless, environmental factors affecting alate production have rarely been studied in field populations of pea aphids.Using data from a three‐year study of alate production in 5–9 alfalfa (lucerne) fields, we examined the effects of (i) pea aphid abundance, (ii) host plant maturity, (iii) temperature, (iv) predator and herbivore abundance, (v) parasitism, and (vi) entomopathic fungal incidence. In twice‐weekly samples taken over the growing season, alate production ranged from 0% to 83% of the nymphal population.Pea aphid abundance, temperature, and alfalfa maturity together explained 67% of the variation in alate production. The other factors we investigated explained little variation. These results suggest there is a limited number of key environmental factors that consistently predict changes in alate production in field populations, while many factors identified in lab studies may be unimportant. Our results highlight the value of investigating factors affecting the expression of plastic traits in insect species at a broad spatiotemporal scale and under natural conditions. [ABSTRACT FROM AUTHOR]

Although asexual lineages evolved from sexual lineages in many different taxa, the genetics of sex loss remains poorly understood. We addressed this issue in the pea aphid Acyrthosiphon pisum , whose natural populations encompass lineages performing cyclical parthenogenesis (CP) and producing one sexual generation per year, as well as obligate parthenogenetic (OP) lineages that can no longer produce sexual females but can still produce males. An SNP-based, whole-genome scan of CP and OP populations sequenced in pools (103 individuals from 6 populations) revealed that an X-linked region is associated with the variation in reproductive mode. This 840-kb region is highly divergent between CP and OP populations (FST = 34.9%), with >2,000 SNPs or short Indels showing a high degree of association with the phenotypic trait. In OP populations specifically, this region also shows reduced diversity and Tajima's D , consistent with the OP phenotype being a derived trait in aphids. Interestingly, the low genetic differentiation between CP and OP populations at the rest of the genome (FST = 2.5%) suggests gene flow between them. Males from OP lineages thus likely transmit their op allele to new genomic backgrounds. These genetic exchanges, combined with the selection of the OP and CP reproductive modes under different climates, probably contribute to the long-term persistence of the cp and op alleles. [ABSTRACT FROM AUTHOR]

Hesperidin is a highly bioactive natural flavonoid whose role in ecological interactions is poorly known. In particular, the effects of hesperidin on herbivores are rarely reported. Flavonoids have been considered as prospective biopesticides; therefore, the aim of the present study was to examine the influence of hesperidin on the host plant selection behavior of three aphid (Hemiptera: Aphididae) species: Acyrthosiphon pisum Harrris, Rhopalosiphum padi (L.), and Myzus persicae (Sulz.). The aphid host plants were treated with 0.1% and 0.5% ethanolic solutions of hesperidin. Aphid probing behavior in the no-choice experiment was monitored using electropenetrography and aphid settling on plants in the choice experiment was recorded. The results demonstrated that hesperidin can be applied as a pre-ingestive, ingestive, and post-ingestive deterrent against A. pisum, as an ingestive deterrent against R. padi, and as a post-ingestive deterrent against M. persicae using the relatively low 0.1% concentration. While in A. pisum the deterrent effects of hesperidin were manifested as early as during aphid probing in peripheral plant tissues, in M. persicae, the avoidance of plants was probably the consequence of consuming the hesperidin-containing phloem sap.

Many plant pathogens are transmitted by generalist insects that move between host species, and vector preference and performance on different hosts affects pathogen transmission. Most studies of host–vector–pathogen interactions focus on a single host, however, and it is relatively unknown if viruses affect the host breadth of vectors. For example, although pea aphids (Acyrthosiphon pisum) often form tight associations with specific hosts, viruses transmitted by aphids can break down host defenses, potentially weakening these associations and increasing the host breadth of their vectors. Here, we assessed vector host preference and performance in an experiment with five pea aphid colonies with distinct host associations, five host species, and two viruses (Pea enation mosaic virus [PEMV] and Bean leafroll virus [BLRV]). Our prediction was that pea aphids would have higher performance on their inferior hosts and be less discriminating among hosts when those are infected, compared with noninfected hosts. Our results show that aphid performance, measured as the rate of increase on hosts, differed among hosts based on their host association, and relative performance among hosts was indeed altered by virus infection. Aphid preferences, measured using a choice bioassay in which aphids could settle on any of the five host species, also differed among aphid colonies but was not affected by virus infection status. We also did not find that infection status of hosts altered the performance of aphids on their preferred host. Furthermore, virus infection did not disrupt preference performance relationships for the aphids. Overall, our study suggests that host preference and performance are deeply ingrained in pea aphids, and that host associations may be robust to the presence of host-manipulating plant pathogens.