Phloem-feeding Insects Research Articles

Plant growth-promoting bacteria Kosakonia radicincitans mediate anti-herbivore defense in Arabidopsis thaliana.

This study demonstrates that the application of the PGPB strain, Kosakonia radicincitans enhances a plant's resistance against phloem-feeding and chewing insects in Arabidopsis thaliana. The plant growth-promoting bacterial strain K. radicincitans DSM 16656 applied to A. thaliana reduced the number of phloem-feeding insects of both the specialist Brevicoryne brassicae and the generalist Myzus persicae. While weight gain of the generalist chewing insect Spodoptera exigua was reduced by 30% on A. thaliana plants treated with K. radicincitans, growth of the specialist caterpillar Pieris brassicae was not affected when compared with caterpillars from control plants. Since generalist and specialist chewing insects responded differentially to PGPB application, the implication of signaling pathways in PGPB mediated changes in plant defense was studied using two signaling pathway mutants impaired in their salicylic acid (npr1-1 mutant) or jasmonic acid (coi1-1 mutant) pathway. We found that the jasmonic acid pathway is relevant for upregulation of aliphatic glucosinolates and suppression of the chewing generalist S. exigua larval growth. Chewing from generalist P. brassicae increased glucosinolate content in A. thaliana leaves mediated via both signaling pathways. However, only in the npr1-1 mutant, which contains the highest aliphatic glucosinolate content, the P. brassicae induced further enrichment of glucosinolates, resulting in a reduction of larval growth. Effects of K. radicincitans on plant resistance could not be explained by changes in glucosinolate contents or composition. Our results demonstrate the distinct role played by K. radicincitans in suppressing insect performance in A. thaliana.

Phloem-feeding herbivory on flowering melon plants enhances attraction of parasitoids by shifting floral to defensive volatiles

Emission of herbivore-induced plant volatiles (HIPVs) can differ according to the type of herbivory and the plant development stage, ultimately affecting recruitment of the natural enemy. Little is known about plant defenses induced at the flowering stage by phloem-feeding insects. We investigated the olfactory preference of Encarsia desantisi parasitoids and the chemical profile of flowering melon plants induced or not by the phloem-feeding of Bemisia tabaci whiteflies. In addition, we tested whether the parasitoids were attracted to synthetic defensive HIPVs, which mimicked whitefly-infested flowering melons. The parasitoids recognized volatiles from undamaged melons but preferred the scent of host-infested melons in olfactometry assays. Amounts of most individual volatiles did not differ between plant treatments; however, only whitefly-induced melons released methyl salicylate and tetradecane, compounds known to attract parasitoids. Interestingly, grouping volatiles by chemical classes revealed that whitefly-infested melon released larger amounts of monoterpenes and smaller amounts of benzenoids than undamaged melons, which might underlying the parasitoid attraction and indicate a possible trade-off between defensive and reproductive defenses at the melon flowering stage. Additionally, E. desantisi preferred the mix of synthetic and defensive HIPVs over hexane (control), opening a new avenue for further investigations in using olfactory lures for B. tabaci biological control. This study is the first report of induced defenses in melon plants and their mediation in a tritrophic interaction, as well as the first record of E. desantisi behavioral preference for HIPVs.

Factors Influencing Insecticide Efficacy against Armored and Soft Scales

Scale insects (Hemiptera: Coccoidea) are among the most economically important pests of ornamental plants. Soft scales (Coccidae) are phloem-feeding insects that produce large amounts of honeydew. By contrast, armored scales (Diaspididae) feed on the contents of plant cells and produce a waxy test that covers their bodies. We studied two species of armored scales [pine needle scale (Chionaspis pinifoliae) and oleander scale (Aspidiotus nerii)] and two species of soft scales [calico scale (Eulecanium cerasorum) and striped pine scale (Toumeyella pini)] to compare efficacy of selected insecticides. In addition, we assessed how the duration of first instar emergence might influence insecticide efficacy. Several reduced-risk insecticides (chlorantraniliprole, pyriproxyfen, spiromesifen, and spirotetramat), horticulture oil, and two broad-spectrum insecticide standards (bifenthrin and dinotefuran) were evaluated. Efficacy of insecticides was consistent within each scale family. Bifenthrin and pyriproxyfen were the only insecticides that killed soft scale insects. By contrast, all insecticides killed armored scales when the crawler stage was the target of application. Armored and soft scales may differ in susceptibility to pesticides because of likely differences in the chemical composition of their integuments and covers. Finally, we found that the effectiveness of a single application of insecticide declined by >15% when the duration of the crawling juvenile period was increased from 1 to 4 weeks. Increases in duration of a scale crawling period decreased the efficacy of a pesticide application.

Targeting detoxification genes by phloem-mediated RNAi: A new approach for controlling phloem-feeding insect pests

Many phloem-feeding insects are considered severe pests of agriculture and are controlled mainly by chemical insecticides. Continued extensive use of these inputs is environmentally undesirable, and also leads to the development of insecticide resistance. Here, we used a plant-mediated RNA interference (RNAi) approach, to develop a new control strategy for phloem-feeding insects. The approach aims to silence “key” detoxification genes, involved in the insect's ability to neutralize defensive and toxic plant chemistry. We targeted a glutathione S-transferase (GST) gene, BtGSTs5, in the phloem-feeding whitefly Bemisia tabaci, a devastating global agricultural pest. We report three major findings. First, significant down regulation of the BtGSTs5 gene was obtained in the gut of B. tabaci when the insects were fed on Arabidopsis thaliana transgenic plants expressing dsRNA against BtGSTs5 under a phloem-specific promoter. This brings evidence that phloem-feeding insects can be efficiently targeted by plant-mediated RNAi. Second, in-silico and in-vitro analyses indicated that the BtGSTs5 enzyme can accept as substrates, hydrolyzed aliphatic- and indolic-glucosinolates, and produce their corresponding detoxified conjugates. Third, performance assays suggested that the BtGSTs5 gene silencing prolongs the developmental period of B. tabaci nymphs. Taken together, these findings suggest that BtGSTs5 is likely to play an important role in enabling B. tabaci to successfully feed on glucosinolate-producing plants. Targeting the gene by RNAi in Brassicaceae cropping systems, will likely not eliminate the pest populations from the fields but will significantly reduce their success over the growing season, support prominent activity of natural enemies, eventually allowing the establishment of stable and sustainable agroecosystem.

Modeling trophic dependencies and exchanges among insects\u2019 bacterial symbionts in a host-simulated environment

BackgroundIndividual organisms are linked to their communities and ecosystems via metabolic activities. Metabolic exchanges and co-dependencies have long been suggested to have a pivotal role in determining community structure. In phloem-feeding insects such metabolic interactions with bacteria enable complementation of their deprived nutrition. The phloem-feeding whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) harbors an obligatory symbiotic bacterium, as well as varying combinations of facultative symbionts. This well-defined bacterial community in B. tabaci serves here as a case study for a comprehensive and systematic survey of metabolic interactions within the bacterial community and their associations with documented occurrences of bacterial combinations. We first reconstructed the metabolic networks of five common B. tabaci symbionts genera (Portiera, Rickettsia, Hamiltonella, Cardinium and Wolbachia), and then used network analysis approaches to predict: (1) species-specific metabolic capacities in a simulated bacteriocyte-like environment; (2) metabolic capacities of the corresponding species’ combinations, and (3) dependencies of each species on different media components.ResultsThe predictions for metabolic capacities of the symbionts in the host environment were in general agreement with previously reported genome analyses, each focused on the single-species level. The analysis suggests several previously un-reported routes for complementary interactions and estimated the dependency of each symbiont in specific host metabolites. No clear association was detected between metabolic co-dependencies and co-occurrence patterns.ConclusionsThe analysis generated predictions for testable hypotheses of metabolic exchanges and co-dependencies in bacterial communities and by crossing them with co-occurrence profiles, contextualized interaction patterns into a wider ecological perspective.

Double-stranded RNA Oral Delivery Methods to Induce RNA Interference in Phloem and Plant-sap-feeding Hemipteran Insects.

Phloem and plant sap feeding insects invade the integrity of crops and fruits to retrieve nutrients, in the process damaging food crops. Hemipteran insects account for a number of economically substantial pests of plants that cause damage to crops by feeding on phloem sap. The brown marmorated stink bug (BMSB), Halyomorpha halys (Heteroptera: Pentatomidae) and the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae) are hemipteran insect pests introduced in North America, where they are an invasive agricultural pest of high-value specialty, row, and staple crops and citrus fruits, as well as a nuisance pest when they aggregate indoors. Insecticide resistance in many species has led to the development of alternate methods of pest management strategies. Double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) is a gene silencing mechanism for functional genomic studies that has potential applications as a tool for the management of insect pests. Exogenously synthesized dsRNA or small interfering RNA (siRNA) can trigger highly efficient gene silencing through the degradation of endogenous RNA, which is homologous to that presented. Effective and environmental use of RNAi as molecular biopesticides for biocontrol of hemipteran insects requires the in vivo delivery of dsRNAs through feeding. Here we demonstrate methods for delivery of dsRNA to insects: loading of dsRNA into green beans by immersion, and absorbing of gene-specific dsRNA with oral delivery through ingestion. We have also outlined non-transgenic plant delivery approaches using foliar sprays, root drench, trunk injections as well as clay granules, all of which may be essential for sustained release of dsRNA. Efficient delivery by orally ingested dsRNA was confirmed as an effective dosage to induce a significant decrease in expression of targeted genes, such as juvenile hormone acid O-methyltransferase (JHAMT) and vitellogenin (Vg). These innovative methods represent strategies for delivery of dsRNA to use in crop protection and overcome environmental challenges for pest management.

Nutrition versus defense: Why Myzus persicae (green peach aphid) prefers and performs better on young leaves of cabbage.

Plant leaves of different ages differ in nutrients and toxic metabolites and thus exhibit various resistance levels against insect herbivores. However, little is known about the influence of leaf ontogeny on plant resistance to phloem-feeding insects. In this study, we found that the green peach aphid, Myzus persicae, preferred to settle on young cabbage leaves compared with mature or old leaves, although young leaves contained the highest concentration of glucosinolates. Furthermore, aphids feeding on young leaves had higher levels of glucosinolates in their body, but aphids performed better on young leaves in terms of body weight and population growth. Phloem sap of young leaves had higher amino acid:sugar molar ratio than mature leaves, and aphids feeding on young leaves showed two times longer phloem feeding time and five times more honeydew excretion than on other leaves. These results indicate that aphids acquired the highest amount of nutrients and defensive metabolites when feeding on young cabbage leaves that are strong natural plant sinks. Accordingly, we propose that aphids generally prefer to obtain more nutrition rather than avoiding host plant defense, and total amount of nutrition that aphids could obtain is significantly influenced by leaf ontogeny or source-sink status of feeding sites.

Computational and biological characterization of fusion proteins of two insecticidal proteins for control of insect pests

Sucking pests pose a serious agricultural challenge, as available transgenic technologies such as Bacillus thuringiensis crystal toxins (Bt) are not effective against them. One approach is to produce fusion protein toxins for the control of these pests. Two protein toxins, Hvt (ω-atracotoxin from Hadronyche versuta) and onion leaf lectin, were translationally fused to evaluate the negative effects of fusion proteins on Phenacoccus solenopsis (mealybug), a phloem-feeding insect pest. Hvt was cloned both N-terminally (HL) and then C-terminally (LH) in the fusion protein constructs, which were expressed transiently in Nicotiana tabacum using a Potato Virus X (PVX) vector. The HL fusion protein was found to be more effective against P. solenopsis, with an 83% mortality rate, as compared to the LH protein, which caused 65% mortality. Hvt and lectin alone caused 42% and 45%, respectively, under the same conditions. Computational studies of both fusion proteins showed that the HL protein is more stable than the LH protein. Together, these results demonstrate that translational fusion of two insecticidal proteins improved the insecticidal activity relative to each protein individually and could be expressed in transgenic plants for effective control of sucking pests.

Targeting symbiosis-related insect genes by RNAi in the pea aphid-Buchnera symbiosis

The growth and reproduction of phloem sap-feeding insects requires the sustained function of intracellular bacteria localized in specialized cells known as bacteriocytes, giving the potential to target the bacterial symbiosis as a novel strategy for controlling sap-feeding insect pests. We focused on two genes in the pea aphid Acyrthosiphon pisum, amiD and ldcA1, which were acquired horizontally from bacteria and have the annotated function to degrade immunogenic bacterial peptidoglycan. We hypothesized that AmiD and LdcA1 function to eliminate peptidoglycan fragments released by the bacterial symbiont Buchnera inhabiting the bacteriocytes, thereby protecting the Buchnera from host attack. Consistent with this hypothesis, expression of amiD and ldcA1 was enriched in bacteriocytes and varied significantly with aphid age, conforming to an inverse curvilinear relationship for amiD and negative linear relationship for ldcA1. RNAi against amiD and ldcA1 administered orally to larval pea aphids caused a significant reduction in Buchnera abundance and activity, accompanied by depressed aphid growth rates. For RNAi experiments, the aphids were co-administered with dsRNA against an aphid nuclease nuc1, protecting the dsRNA against non-specific degradation. These experiments demonstrate that selective suppression of insect symbiosis-related gene function can reduce the performance of an insect pest. Phylogenetic analysis identified amiD and ldcA1 in sequenced genomes of other aphid species, and amiD in related groups of phloem-feeding insects, offering the opportunity for specific controls against a range of insect pests.

Generic synopsis of the jumping plant-lice (Hemiptera: Sternorrhyncha: Psylloidea) from Colombia.

Jumping plant-lice (Hemiptera: Sternorrhyncha: Psylloidea) are a group of phloem-feeding insects with nearly 4000 described species. Previous records from Colombia comprise 19 genera of all eight known families. The revision of material deposited in six Colombian and three foreign museums yielded another nine genera that constitute new country records. Material from 16 departments was examined. Each genus is diagnosed and information is provided on biology, damage and host-plants. Local distribution maps and a generic key for the identification of adults are provided.

Induction of Systemic Resistance against Insect Herbivores in Plants by Beneficial Soil Microbes.

Soil microorganisms with growth-promoting activities in plants, including rhizobacteria and rhizofungi, can improve plant health in a variety of different ways. These beneficial microbes may confer broad-spectrum resistance to insect herbivores. Here, we provide evidence that beneficial microbes modulate plant defenses against insect herbivores. Beneficial soil microorganisms can regulate hormone signaling including the jasmonic acid, ethylene and salicylic acid pathways, thereby leading to gene expression, biosynthesis of secondary metabolites, plant defensive proteins and different enzymes and volatile compounds, that may induce defenses against leaf-chewing as well as phloem-feeding insects. In this review, we discuss how beneficial microbes trigger induced systemic resistance against insects by promoting plant growth and highlight changes in plant molecular mechanisms and biochemical profiles.

Pest categorisation of Witches' broom disease of lime (Citrus aurantifolia) phytoplasma.

The EFSA Panel on Plant Health performed a pest categorisation for the Witches' broom disease of lime (Citrus aurantifolia) phytoplasma for the EU territory. The pest has been reported in a few countries in the Middle East and is not known to occur in the EU. The disease is caused by a well‐defined phytoplasma strain in the ‘Candidatus Phytoplasma aurantifolia' species, for which efficient molecular detection assays are available. The most important known natural host is Citrus aurantifolia, which is only grown for ornamental purposes in the EU. Sweet limes, rough lemon and trifoliate orange are also naturally infected by that phytoplasma. The latter can be transmitted by grafting also to some citrus species. Other citrus species were reported to be resistant; however, their susceptibility has been assessed only by symptom observations, and the possible presence of phytoplasmas in symptomless plants cannot be ruled out. The phytoplasma is transmitted by the leafhopper Hishimonus phycitis, which is not known to occur in the EU. There is no information on the vector status of other phloem feeding insects of citrus present in the EU. The pest is listed in Annex IIAI of Directive 2000/29/EC. The main pathways for entry, plants for planting and the vector insect, are closed by existing legislation on import of citrus plants. Nevertheless, should the pest enter, it could establish and spread. In countries where Witches' broom disease of lime (WBDL) is present, it has significant impact. The main knowledge gaps concern (1) and vertical transmission of the phytoplasma to H. phycitis eggs (2) lack of information regarding susceptibility of citrus crops grown in the EU (3) status of potential insect vectors in the EU. Therefore, the WBDL phytoplasma meets the criteria assessed by EFSA for consideration as a potential Union quarantine pest.

Impaired expressions of the beta and delta isoforms of vacuolar processing enzymes compromise the basal defenses of Arabidopsis thaliana against the phloem-feeding insect Myzus persicae

While the functions of vacuolar processing enzymes (VPE) in plant responses to pathogens are now better established, their possible roles against insect herbivores need validation. Inspired by an observation that βVPE and δVPE represent the most highly upregulated transcripts in leaves of Solanum bulbocastanum and its backcross progenies that were highly resistant to the phloem-feeding green peach aphids (Myzus persicae), we used a reverse genetic approach in Arabidopsis to investigate whether T-DNA insertion mutants for specific βVPE and δVPE loci would exhibit compromised defenses at the whole-plant, physiological, and molecular levels. We hypothesized that impaired expression of VPE genes would lead to hyper-susceptibility if VPE-mediated processes were essential for basal defenses, given that Arabidopsis is naturally susceptible. Compared to the wild-type, βvpe and δvpe mutants exhibited an early onset of leaf curling and necrosis, rapid aphid population build-up, and significant physiological tissue injuries as a result of herbivory. This indicates that basal defenses were compromised by the loss-of-functions of either VPE-encoding gene. VPE co-expression networks were comprised of genes involved in sucrose metabolism and transport (AtSUC5, AtSUS3, and invertases), efflux and oxidative detoxification proteins, and modulators of gene-for-gene-type disease response linked to sucrose metabolism (AtSWEET13 and AtSWEET15). These results suggest that VPEs play a role in basal defenses by mediating mechanisms of detoxification and metabolite availability in host tissues to counteract the rapid depletion caused by the phloem sucker. These processes might be important as first line of defense to delay the progression of perturbations caused by herbivory.

Redox Control of Aphid Resistance through Altered Cell Wall Composition and Nutritional Quality.

The mechanisms underpinning plant perception of phloem-feeding insects, particularly aphids, remain poorly characterized. Therefore, the role of apoplastic redox state in controlling aphid infestation was explored using transgenic tobacco (Nicotiana tabacum) plants that have either high (PAO) or low (TAO) ascorbate oxidase (AO) activities relative to the wild type. Only a small number of leaf transcripts and metabolites were changed in response to genotype, and cell wall composition was largely unaffected. Aphid fecundity was decreased significantly in TAO plants compared with other lines. Leaf sugar levels were increased and maximum extractable AO activities were decreased in response to aphids in all genotypes. Transcripts encoding the Respiratory Burst Oxidase Homolog F, signaling components involved in ethylene and other hormone-mediated pathways, photosynthetic electron transport components, sugar, amino acid, and cell wall metabolism, were increased significantly in the TAO plants in response to aphid perception relative to other lines. The levels of galactosylated xyloglucan were decreased significantly in response to aphid feeding in all the lines, the effect being the least in the TAO plants. Similarly, all lines exhibited increases in tightly bound (1→4)-β-galactan. Taken together, these findings identify AO-dependent mechanisms that limit aphid infestation.

Mechanisms of aggregation in an ant-tended treehopper: Attraction to mutualists is balanced by conspecific competition.

Understanding the spatial structure of populations and communities has been a dominant focus of ecological research, and spatial structure is increasingly seen as critical for understanding population dynamics. Habitat (or host) preference is a proximate mechanism that can generate aggregation or overdispersion, lending insight into the ultimate consequences of observed spatial distributions. Publilia concava is a univoltine phloem-feeding insect that forms mutualistic associations with ants, which consume honeydew and protect treehoppers from predation. Treehopper adults and nymphs are aggregated at the scale of goldenrod plant stems, and previous studies have suggested that this aggregation is an adaptive response that increases feeding performance or maximizes benefits of ant-tending. Previous studies have also shown experimentally that individual treehoppers preferentially oviposit on plants with ants present, but a complimentary hypothesis that treehoppers prefer to oviposit near conspecifics (e.g., to take advantage of density-dependent ant attraction) remains untested. We show that, as expected, the probability of treehopper oviposition increases with ant-presence and relative ant abundance. However, we also find that treehopper oviposition decreases with increasing treehopper density. Thus our results are inconsistent with the hypothesis that treehopper aggregation is a socially cooperative strategy to attract ants; we suggest that aggregation is a form of conflict and an unavoidable by-product of individual responses to ant-tending levels.

1H NMR analysis of Citrus macrophylla subjected to Asian citrus psyllid (Diaphorina citri Kuwayama) feeding

The Asian citrus psyllid (ACP) is a phloem-feeding insect that can host and transmit the bacterium Candidatus Liberibacter asiaticus (CLas), which is the putative causative agent of the economically important citrus disease, Huanglongbing (HLB). ACP are widespread in Florida, and are spreading in California; they are the primary mode of CLas transmission in citrus groves. To understand the effects of ACP feeding, different numbers of ACP [0 ACP (control), 5 ACP (low), 15–20 ACP (medium), and 25–30 ACP (high)] were allowed to feed on Citrus macrophylla greenhouse plants. After 7 days of feeding, leaves were collected and analyzed using 1H NMR. Metabolite concentrations from leaves of trees with ACP feeding had higher variability than control trees. Many metabolites were higher in concentration in the low ACP feeding group relative to control; however, leaves from trees with high ACP feeding had lower concentrations of many metabolites relative to control, including many amino acids such as phenylalanine, arginine, isoleucine, valine, threonine, and leucine. These results suggest ACP density-dependent changes in primary metabolism that can be measured by 1H NMR. The implications in plant defense are discussed.

Three MYB genes co-regulate the phloem-based defence against English grain aphid in wheat.

Plant phloem-based defence (PBD) against phloem-feeding insects is characteristic of the sieve occlusion by phloem lectins and β-1,3-glucan callose, both of which are produced under regulation by ethylene and MYB transcription factors. Wheat PBD requires β-1,3-glucan synthase-like proteins GSL2, GSL10, and GSL12, and may also require insect-resistant mannose-binding lectins Hfr-1 and Wci-1, which can accumulate in the phloem upon aphid feeding. This study elucidates whether any of the 73 MYB genes identified previously in the common wheat Triticum aestivum genome plays a role in wheat PBD activation with regard to the GSLs and lectins. Wheat MYB genes TaMYB19, TaMYB29, and TaMYB44 are highly activated in response to infestation of English grain aphid, and their silencing facilitates aphid feeding on wheat phloem and represses wheat PBD responses. Repressed PBD is shown to decrease aphid-induced callose deposition in wheat leaf epidermis and decrease aphid-induced expression of genes GSL2, GSL10, GSL12, Hfr-1, and Wci-1 in wheat leaf tissues. Based on single gene silencing effects, TaMYB19, TaMYB29, and TaMYB44 contribute 55-82% of PBD responses. However, the contributions of TaMYB genes to PBD are eliminated by ethylene signalling inhibitors, while simultaneous silencing of the three TaMYB genes cancels the tested PBD responses. Therefore, TaMYB19, TaMYB29, and TaMYB44 are co-regulators of wheat PBD and execute this function through crosstalk with the ethylene signalling pathway.

Silicon amendment is involved in the induction of plant defense responses to a phloem feeder

Plant resistance to herbivores is a key component in integrated pest management. In most cases, silicon (Si) amendment to plants enhances resistance to herbivorous insects. The increase of plant physical barrier and altered insect behaviors are proposed as mechanisms for the enhanced resistance in Si-amended plants, but our understanding of the induced mechanisms involved in Si-enhanced plant resistance to phloem-feeding insects remains unclear. Here, we show that Si amendment to rice (Oryza sativa) plants impacts multiple plant defense responses induced by a phloem-feeder, the brown planthopper (Nilaparvata lugens, BPH). Si amendment improved silicification of leaf sheaths that BPH feed on. Si addition suppressed the increase of malondialdehyde concentration while encouraged increase of H2O2 concentration in plants attacked by BPH. Higher activities of catalase and superoxide dismutase were recorded in Si-amended than in non-amended BPH-infested plants. BPH infestation activated synthases for secondary metabolites, polyphenol oxidase and pheny-lalanine ammonia-lyase, and β-1,3-glucanase, but the activation was greater in Si-amended than in non-amended plants. Taken together, our findings demonstrate that Si amendment interacts with BPH infestation in the induction of plant defense responses and consequently, to confer enhanced rice plant resistance.

Host plant and competitor identity matter in genotype × genotype × environment interactions between vetch and pea aphids

1. Selection does not only operate in a genotype (G) × environment (E) context, but can also be modulated by the activities of organisms interacting with their environment (G × G × E). 2. The influences of aphid clonal identity and host plant (Vicia faba) intraspecific genetic variation on the performance of five genotypes of pea aphid (Acyrthosiphon pisum) were investigated – with and without interaction with a competing heterospecific clone of vetch aphid (Megoura viciae) – across three cultivars of V. faba. 3. Pea aphid performance in the presence of a competing vetch aphid clone (G × G × E) compared with the absence of competition (G × E) revealed strong context-dependent, genotype-specific shifts in performance, influenced by plant cultivar, competitor presence and their interaction. 4. The performance of vetch aphid in competition with each pea aphid clone was also compared. Here, competitor's genotype and abundance underlay a remarkably varied response by vetch aphid across interactions. 5. The study shows that aphid genotypes exhibit a varying degree of risk spreading, contingent on competitor identity and the patterns of aggregation across three plant cultivars. Owing to feedback loops between species activities and selective forces acting on them, our findings suggest that there are context-dependent responses by competitors that are shaped via the interplay of the co-occurring species and their biotic environment. 6. This work highlights the complexity of species interactions and the importance of investigating reciprocity between competition and intraspecific genetic variation. A better understanding of the eco-evolutionary interactions between phloem-feeding insects and their host plants can potentially be used to enhance crop protection and pest control.

A Phloem-Feeding Insect Transfers Bacterial Endophytic Communities between Grapevine Plants.

Bacterial endophytes colonize the inner tissues of host plants through the roots or through discontinuities on the plant surface, including wounds and stomata. Little is known regarding a possible role of insects in acquiring and transmitting non-phytopathogenic microorganisms from plant to plant, especially those endophytes that are beneficial symbionts providing plant protection properties and homeostatic stability to the host. To understand the ecological role of insects in the transmission of endophytic bacteria, we used freshly hatched nymphs of the American sap-feeding leafhopper Scaphoideus titanus (vector) to transfer microorganisms across grapevine plants. After contact with the vector, sink plants were colonized by a complex endophytic community dominated by Proteobacteria, highly similar to that present in source plants. A similar bacterial community, but with a higher ratio of Firmicutes, was found on S. titanus. Insects feeding only on sink plants transferred an entirely different bacterial community dominated by Actinobacteria, where Mycobacterium sp., played a major role. Despite the fact that insects dwelled mostly on plant stems, the bacterial communities in plant roots resembled more closely those inside and on insects, when compared to those of above-ground plant organs. We prove here the potential of insect vectors to transfer entire endophytic bacterial communities between plants. We also describe the role of plants and bacterial endophytes in establishing microbial communities in plant-feeding insects.