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International audience; The One Health approach to understanding disease epidemiology and achieving surveillance and prevention is holistic all while focusing on zoonotic diseases. Many of its principles are similar to those espoused in Agroecology, begetting the question of what One Health can contribute - in practice - to preventing plant disease. Here we describe four knowledge challenges for plant health management that have arisen from the One Health experience for zoonotic diseases that could boost prospects for novel approaches to plant disease surveillance, prediction and prevention. The challenges are to i) uncover reservoirs and revise pathogen life histories, ii) elucidate drivers of virulence beyond the context of direct host-pathogen interactions, iii) account for the natural highways of long distance dissemination (i.e., surface water and air mass movement), and iv) update disease forecasts in the face of changing land use, cultivation practices and climate. Furthermore, we note that implementation of a One Health approach to disease surveillance and prevention will require mobilization of tools to deal with the representation and accessibility of massive and heterogeneous data and knowledge; with knowledge inference, data science, modelling, and pattern recognition; and multi-actor approaches that unite different sectors of society as well as different scientific disciplines. The infrastructure to build and the obstacles to overcome for a bona fide One Health approach to disease surveillance and prevention are the key commonalities where actors in the efforts to prevent zoonotic diseases and plant disease can work together for human, animal and plant health and sustainable management of biodiversity.

International audience; Vector management is a cornerstone in the fight against vector-borne pathogens. However, the impact on ecosystem functioning of reducing or eliminating arthropod vector populations remains poorly understood. Vectors are members of complex ecological communities, and recent studies suggest that their population suppression alters food web dynamics (bottom-up and top-down trophic cascades), inter- and intraspecific competition, and plant pollination. Other possible overlooked roles are also proposed. In this review, with examples from vectors of plant, animal, and human pathogens, we highlight that, although the ecological roles of most vector species might be redundant with other non-vector species, changes in vector abundance alter biotic interactions and, thus, are unlikely to be neutral in terms of ecosystem functioning

Inferring the dispersal processes of vector-borne plant pathogens is a great challenge because the plausible epidemiological scenarios often involve complex spread patterns at multiple scales. The spatial genetic structure of ‘Candidatus Phytoplasma prunorum’, responsible for European stone fruit yellows disease, was investigated by the application of a combination of statistical approaches to genotype data of the pathogen sampled from cultivated and wild compartments in three French Prunus-growing regions. This work revealed that the prevalence of the different genotypes is highly uneven both between regions and compartments. In addition, we identified a significant clustering of similar genotypes within a radius of 50 km or less, but not between nearby wild and cultivated Prunus. We also provide evidence that infected plants are transferred between production areas, and that both species of the Cacopsylla pruni complex can spread the pathogen. Altogether, this work supports a main epidemiological scenario where ‘Ca. P. prunorum’ is endemic in — and generally acquired from — wild Prunus by its immature psyllid vectors. The latter then migrate to shelter plants that epidemiologically connect sites less than 50 km apart by later providing infectious mature psyllids to their “migration basins”. Such multi-scale studies could be useful for other pathosystems.

Alfalfa leaf curl virus (ALCV) is the first geminivirus for which aphid transmission was reported. Transmission by Aphis craccivora was determined previously to be highly specific and circulative. Using various complementary techniques, the transmission journey of ALCV was monitored from its uptake from infected plant tissues up to the head of its vector. ALCV was shown to be restricted to phloem tissues using fluorescence in situ hybridization (FISH) and electropenetrography (EPG) monitoring of virus acquisition. Furthermore, the virus is heterogeneously distributed in phloem tissues, as revealed by FISH and quantitative PCR of viral DNA acquired by EPG-monitored aphids. Despite the efficient ingestion of viral DNA, about 106 viral DNA copies per insect in a 15 h feeding period on ALCV-infected plants, the individual maximum transmission rate was 12 %. Transmission success was related to a critical viral accumulation, around 1.6×107 viral DNA copies per insect, a threshold that generally needed more than 48 h to be reached. Moreover, whereas the amount of acquired virus did not decrease over time in the whole aphid body, it declined in the haemolymph and heads. ALCV was not detected in progenies of viruliferous aphids and did not affect aphid fitness. Compared to geminiviruses transmitted by whiteflies or leafhoppers, or to luteoviruses transmitted by aphids, the transmission efficiency of ALCV by A. craccivora is low. This result is discussed in relation to the aphid vector of this geminivirus and the agroecological features of alfalfa, a hardy perennial host plant.

Inferring the dispersal processes of vector-borne plant pathogens is a great challenge because the plausible epidemiological scenarios often involve complex spread patterns at multiple scales. European stone fruit yellows (ESFY), a disease caused by ‘CandidatusPhytoplasma prunorum’ and disseminated via planting material and vectors belonging to the speciesCacopsylla pruni, is a major threat for stone fruit production throughout Europe. The spatial genetic structure of the pathogen was investigated at multiple scales by the application of a combination of statistical approaches to a large dataset obtained through the intensive sampling of the three ecological compartments hosting the pathogen (psyllids, wild and cultivatedPrunus) in threePrunus-growing regions in France. This work revealed new haplotypes of ‘Ca. P. prunorum’, and showed that the prevalence of the different haplotypes of this pathogen is highly uneven between all regions, and within two of them. In addition, we identified a significant clustering of similar haplotypes within a radius of at most 50 km, but not between nearby wild and cultivatedPrunus. We also provide evidence that the two species of theC. prunicomplex are unevenly distributed but can spread the pathogen, and that infected plants are transferred between production areas. Altogether, this work supports a main epidemiological scenario where ‘Ca. P. prunorum’ is endemic in, and mostly acquired from, wildPrunusby immatureC. pruni(of both species) who then migrate to “shelter plants” that epidemiologically connect sites less than 50 km apart by later providing infectious matureC. prunito their “migration basins”, which differ in their haplotypic composition. We argue that such multiscale studies would be very useful for other pathosystems.

Determining how reproductive barriers modulate gene flow between populations represents a major step toward understanding the factors shaping the course of speciation. Although many indices quantifying reproductive isolation (RI) have been proposed, they do not permit the quantification of cross-direction-specific RI under varying species frequencies and over arbitrary sequences of barriers. Furthermore, techniques quantifying associated uncertainties are lacking, and statistical methods unrelated to biological process are still preferred for obtaining confidence intervals and P-values. To address these shortcomings, we provide new RI indices that model changes in gene flow for both directions of hybridization, and we implement them in a Bayesian model. We use this model to quantify RI between two species of the psyllid Cacopsylla pruni based on field genotypic data for mating individuals, inseminated spermatophores and progeny. The results showed that preinsemination isolation was strong, mildly asymmetric, and indistinguishably different between study sites despite large differences in species frequencies; that postinsemination isolation strongly affected the more common hybrid type; and that cumulative isolation was close to complete. In the light of these results, we discuss how these developments can strengthen comparative RI studies.

Alfalfa leaf curl virus (ALCV) is the first geminivirus for which aphid transmission was reported. Transmission byAphis craccivorawas determined previously to be highly specific and circulative. Using various complementary techniques, the transmission journey of ALCV was monitored from its uptake from infected plant tissues up to the head of its vector. ALCV was shown to be restricted to phloem tissues using fluorescencein situhybridization (FISH) and electropenetrography (EPG) monitoring of virus acquisition. Furthermore, the virus is heterogeneously distributed in phloem tissues, as revealed by FISH and quantitative PCR of viral DNA acquired by EPG-monitored aphids. Despite the efficient ingestion of viral DNA, about 106viral DNA copies per insect in a 15 h feeding period on ALCV-infected plants, the individual maximum transmission rate was 12 %. Transmission success was related to a critical viral accumulation, around 1.6×107viral DNA copies per insect, a threshold that generally needed more than 48 h to be reached. Moreover, whereas the amount of acquired virus did not decrease over time in the whole aphid body, it declined in the haemolymph and heads. ALCV was not detected in progenies of viruliferous aphids and did not affect aphid fitness. Compared to geminiviruses transmitted by whiteflies or leafhoppers, or to luteoviruses transmitted by aphids, the transmission efficiency of ALCV byA. craccivorais low. This result is discussed in relation to the aphid vector of this geminivirus and the agroecological features of alfalfa, a hardy perennial host plant.

Two members of the genus Capulavirus (Geminiviridae) are transmitted by aphids including Alfalfa leaf curl virus (ALCV) transmitted by Aphis craccivora. The capulavirus Euphorbia caput-medusae latent virus was shown here to be transmitted also by A. craccivora, using the population EuphorbiaSA. ALCV was transmissible by several A. craccivora populations including Robinia, but not EuphorbiaSA, reflecting a high transmission specificity. ALCV accumulation and localization were analyzed in whole insects, midguts, hemolymphs, and heads of aphids from both populations and from the non-vector species Acyrthosiphon pisum. A 6-day persistence was observed in A. craccivora populations but not in A. pisum. Vector and non-vector A. craccivora populations could be distinguished by contrasted virus accumulations and midgut intracellular localization. Results confirm that ALCV is transmitted according to a circulative-persistent mode, and are consistent with a gut barrier to the transmission of ALCV in A. pisum and a primary salivary gland barrier in A. craccivora.

BGPI : équipe 6; International audience; ‘Candidatus Phytoplasma’ species are mostly transmitted from plant to plant by phloem feeding hemipterans, primarily leafhoppers (Cicadellidae) and planthoppers (Fulgoroidea) (Hemiptera, Auchenorrhyncha). However, there is one group of phytoplasmas, the 16SrX or apple proliferation group, whose members are transmitted by psyllid vectors of the superfamily Psylloidea (Hemiptera, Sternorrhyncha). These psyllid-transmitted phytoplasmas are genetically closely related and are associated with economically important diseases of fruit trees such as pear decline, apple proliferation and European stone fruit yellows. The psyllid vector species of these phytoplasmas are also closely related and all belong to the genus Cacopsylla. Both, phytoplasmas and psyllid vectors, are geographically limited to the Palaearctic region, mainly Europe. Only pear decline and peach yellow leaf roll phytoplasmas have probably been introduced to America along with their vectors. As phytoplasma-infected trees cannot be cured and resistant plant material is not available to the growers, preventive control measures such as vector control are of paramount importance to limit the spread of these diseases. Thus, detailed knowledge about the biology and ecology of the vector species, their host plants as well as knowledge about the transmission parameters is crucial.

Single-stranded DNA (ssDNA) plant viruses belong to the families Geminiviridae and Nanoviridae. They are transmitted by Hemipteran insects in a circulative, mostly non-propagative, manner. While geminiviruses are transmitted by leafhoppers, treehoppers, whiteflies and aphids, nanoviruses are transmitted exclusively by aphids. Circulative transmission involves complex virus&ndash, vector interactions in which epithelial cells have to be crossed and defense mechanisms counteracted. Vector taxa are considered a relevant taxonomic criterion for virus classification, indicating that viruses can evolve specific interactions with their vectors. Thus, we predicted that, although nanoviruses and geminiviruses represent related viral families, they have evolved distinct interactions with their vector. This prediction is also supported by the non-structural Nuclear Shuttle Protein (NSP) that is involved in vector transmission in nanoviruses but has no similar function in geminiviruses. Thanks to the recent discovery of aphid-transmitted geminiviruses, this prediction could be tested for the geminivirus alfalfa leaf curl virus (ALCV) and the nanovirus faba bean necrotic stunt virus (FBNSV) in their common vector, Aphis craccivora. Estimations of viral load in midgut and head of aphids, precise localization of viral DNA in cells of insect vectors and host plants, and virus transmission tests revealed that the pathway of the two viruses across the body of their common vector differs both quantitatively and qualitatively.

Flowers are a remarkable component of everyday life. Their diversity of shape, colour and fragrance witnesses the importance of the joint evolutionary processes resulting from the interactions between plants and their insect pollinators. Indeed, pollination mutualisms with insects are key factors that have allowed the evolutionary success and diversification of flowering plants (McKey & Hossaert-McKey, 2008). This diversification of plants has led to an even more impressive diversification of insects. This chapter retraces the main steps of the past history of diversification of pollination interactions with the emergence of some major pollinator groups of insects and proposes some insights into the selective processes acting on the evolution of the entomophilous pollination.

BGPI : équipe 6; The leafhopper Scaphoideus titanus (Hemiptera: Cicadomorpha: Cicadellidae), an invasive deltocephaline species introduced into Europe from North America, is the vector of the most important phytoplasma disease in European viticulture, flavescence dorée. In this first electropenetrography (EPG) study of S. titanus, we characterized its feeding waveforms and defined their biological meanings. Four typical waveform phases (pathway, X wave, sustained ingestion, and interruption) and four families within those phases (A, B, C, and N) were characterized using DC EPG technology. We proposed biological meanings for these waveforms based on excreta pH-ingestion correlations, presence of X waves, and comparison with previous AC, DC, and AC-DC EPG waveforms conducted on Cicadomorpha. We observed that sustained (i.e., >10 min) ingestion by a deltocephaline leafhopper can occur from both xylem and phloem vascular cells. Waveform C2x represented ingestion of xylem fluid, and two waveforms represented behaviors when stylets were inserted into phloem sieve elements: C2p variant 1 (C2p-1), which may represent salivation (perhaps simultaneous with ingestion), and C2p variant 2 (C2p-2), which represented active ingestion. Furthermore, we found that the EPG-recorded X wave has a dual meaning by occurring prior to sustained ingestion from either phloem or xylem. This X wave was very similar in appearance to the model X wave of sharpshooters, an entirely different leafhopper subfamily, Cicadellinae. All cicadellines are obligate xylem-ingesters. Such a “dual-meaning X wave” will provide insights into how the feeding tactics of S. titanus relate to other sheath-feeding hemipterans, and will provide support for future research to clarify the role of this leafhopper as a vector of plant pathogens.

BGPI : équipe 6; In phytophagous piercing-sucking insects, salivary sheath-feeding species are often described as xylem- or phloem-sap feeding specialists. Because these two food sources have very different characteristics, two feeding tactics are often associated with this supposed specialization. Studying the feeding behavior of insects provides substantial information on their biology, ecology, and evolution. Furthermore, study of feeding behavior is of primary importance to elucidate the transmission ability of insects that act as vectors of plant pathogens. In this study, we compared the durations of ingestion performed in xylem versus phloem by a leafhopper species, Scaphoideus titanus Ball, 1932. This was done by characterizing and statistically analyzing electrical signals recorded using the electropenetrography technique, derived from the feeding behaviors of males and females. We identified three groups of S. titanus based on their feeding behavior: 1) a group that reached the phloem quickly and probed for a longer time in phloem tissue than the other groups, 2) a group that reached the xylem quickly and probed for a longer time in xylem tissue than the other groups, and 3) a group where individuals did not ingest much sap. In addition, the numbers and durations of waveforms representing ingestion of xylem and phloem saps differed significantly depending on the sex of the leafhopper, indicating that the two sexes exhibit different feeding behaviors. Males had longer phloem ingestion events than did females, which indicates that males are greater phloem feeders than females. These differences are discussed, specifically in relation to hypotheses about evolution of sap feeding and phytoplasma transmission from plant to plant.

European stone fruit yellows (ESFY) is an EU-listed I/AII disease affecting Prunus spp. caused by ‘Candidatus Phytoplasma prunorum’. This paper reports the results from a systematic literature review approach that sought to determine the geographic distribution of ‘Ca. Phytoplasma prunorum’ in European fruit-growing areas. Evidence for the presence of the phytoplasma was found for 15 of the 27 EU countries. It is prevalent in the most important stone fruit production areas of Central and Southern Europe, where it causes substantial impact in apricots (Prunus armeniaca), Japanese plums (P. salicina) and peaches (P. persica). In Northern European areas where these hosts are not produced, it is occasionally found on tolerant species (P. domestica). However, because surveys of the disease status of tolerant hosts are not performed, it remains unclear whether the pathogen is absent in Northern Europe or survives in tolerant cultivated or wild hosts. No reports of ESFY were found from the southernmost part of Europe: Portugal, Spain (Andalucia, Castile–La Mancha), Italy (Sicily, Puglia), Greece (Crete), Cyprus and Malta. This may be explained by the absence of the favoured wild hosts of the vector. Moreover, it remains unclear if the vector finds suitable conditions for aestivation and overwintering in these regions.

Fruit tree diseases caused by phytoplasma have great economic effects on fruit production, especially in Europe. A major phytoplasma is ‘Candidatus Phytoplasma mali’, which causes apple proliferation (AP) disease mainly in cultured and wild forms of apple trees (Seemuller et al., 2011a); however, there has been a report of different hosts, including Prunus avium (L.) L., P. armeniaca L., and P.domestica L. (Mehle et al., 2007). ‘Ca. Phytoplasma pyri’ causes pear decline (PD) disease that is found mainly in cultured and wild forms of pear (Pyrus spp.) and quince (Cydonia oblonga Mill.) (Seemuller et al., 2011b). These phytoplasma are taxonomically classified into the 16SrX group (or AP-group) of phytoplasmas and constitute closely related subgroups (Seemuller and Schneider, 2004). Phytoplasmas are mainly spread by vegetative propagation or the grafting of infected plant material and phloem feeding insects, primarily leafhoppers, planthoppers and psyllids (Weintraub and Beanland, 2006). Only one genus of this last one, Cacopsylla spp., transmit AP-group phytoplasmas to pome and stone fruit trees. In apple orchards, ‘Ca. P. mali’ can be transmitted by two psyllid species. Cacopsylla (Thamnopsylla) picta (Foerster, 1848) (syn. C. costalis) has been reported main vector in Germany (Jarausch et al., 2003, 2011) and northern Italy (Frisinghelli et al., 2000; Carraro et al., 2008), while Cacopsylla (Thamnopsylla) melanoneura (Foerster, 1848) was identified as main vector in Aosta Valley (Tedeschi et al., 2002). C. picta is monophagous on Malus spp. and until now this species have been described only in Europe (Burckhardt, 1994; Ossiannilsson, 1992; Ouvrard, 2014) and Turkey (Klimaszewski and Lodos, 1977, 1979; Drohojowska and Burckhardt, 2014). C. melanoneura has a Palaearctic distribution and is oligophagous on Rosaceae, its principal host plant being a common shrub, hawthorn (Crataegus monogyna L.) (Ouvrard, 2014). In most of studied cases, both psyllid species are present in apple orchards (Jarausch et al., 2003; Delic et al., 2005; Carraro et al., 2008; Mattedi et al., 2008). Two others species living on hawthorn, Cacopsylla peregrina (Foerster, 1848) and Cacopsylla (Thamnopsylla) affinis (Low, 1880), were found able to harbor the phytoplasmas of the AP-group, in particular ‘Ca. P. mali’ (Tedeschi et al., 2009). Their transmission ability was not proven but this result highlights the potential role as vector of these psyllid species. In pear orchards, until recently, two psyllid species were known as vector of ‘Ca. P. pyri’. Cacopsylla (Hepatopsylla) pyricola (Foerster, 1848) has been reported for Great Britain (Davies et al., 1992) and North America (Jensen et al., 1964), while Cacopsylla (Hepatopsylla) pyri (Linne, 1758) was described as the vector in France (Lemoine 1984), Italy (Carraro et al., 1998a) and Spain (Garcia-Chapa et al., 2005). C. pyri is widespread in Europe, in the Caucasus, Georgia, the Middle Asia, including Turkey (Klimaszewski and Lodos, 1979; Burckhardt and Pak. J. Agri. Sci., Vol. 53(2), 383-392; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.3804 http://www.pakjas.com.pk

Bgpi : équipe 6 chapitre 34; Une relation trophique originale : la vection entomophile d'agents pathogènes

International audience; Concanavalin A (lectin from Canavalia ensiformis L., ConA) has previously been shown to act as a feeding inhibitor for Acyrthosiphon pisum, the pea aphid. In the present study a range of histochemical and biochemical techniques were used to elucidate the target tissues and binding sites of the lectin in the aphid. Diet uptake was evaluated using a radioactive tracer (14C-methylated inulin) and demonstrated that adults were capable of ingesting high quantities of the toxin (approx. 1 microg over a 48 h period). Electophoretic analysis and enzyme-linked immuno-sorbent assay of honeydew samples confirmed these results and further demonstrated that only small levels of ConA were excreted. Histofluorescence and immunolocalisation studies on nymphs revealed that the stomach was the primary target for ConA. At concentrations up to 400 microg ml(-1), lectin binding only occurred in the stomach region, however, at high concentrations (800 microg ml(-1)) the whole digestive tract was stained, although there was no evidence of binding in either the oesophagus or rectum. In addition to binding, there was evidence to suggest that ConA was also causing systemic effects in that the lectin appeared to cross the intestinal epithelial barrier. Immunohistochemical and electron microscopy studies revealed that ConA induced severe cellular swelling of the epithelial cells, accompanied by hypersecretion and a progressive detachment of the apical membrane; however, the striated border itself did not appear to be directly affected. Furthermore, there was no lysis of the epithelium, nor loss of integrity of the epithelial cells themselves. Our results suggest that ConA interacts with glycosylated receptors at the surface of the stomach epithelial cells, interfering with normal metabolism and cell function, resulting in a rapid feedback response on feeding behaviour. Whilst our results provide a much greater understanding regarding the modes of action of ConA in insects, they suggest that different lectins, including other mannose binding lectins, have different modes of action at the cellular levels, and thus generalizations should be treated with caution.

The whitefly Bemisia tabaci (Gennadius) B-Biotype is a major pest on cucurbits in the Caribbean islands. Five field trials were conducted to identify resistance among 80 genotypes of Cucumis melo L. from diverse geographic origins. We focused on resistant rather than tolerant genotypes by counting adults on the abaxial side of two leaves of each plant at least three times in each trial, and larval density of under leaf disk samples at least twice in each trial. On the basis of insect density, three Indian accessions, PI 414723, PI 164723, and 90625, and one Korean accession, PI 161375, had field resistance. On those accessions, we observed 3.6 to 6 times fewer adults than on the most susceptible genotypes (`AR Top Mark' or `Délice de Table') and 11 to 29 times fewer larvae than on `AR Top Mark' or B66-5. Those levels of resistance may be sufficient to significantly reduce pesticide use in Guadeloupe (Lesser Antilles) where B. tabaci populations are lower than in the Southern United States or in the Mediterranean Basin. Higher levels of resistance are needed for genetic control, and may be achieved by a combination of different partial resistance genes.

In the melon, the Vat (monogenic, dominant) resistance gene governs both an antixenotic reaction to the melon aphid Aphis gossypii Glover (Homoptera, Aphididae) and a resistance to non-persistent virus transmission, restricted to this vector species. We investigated the behavioural features and tissue localisation of the antixenosis resistance by the electrical penetration graph technique (EPG, DC system). We also compared the chemical composition in amino compounds and proteins of the phloem sap collected from two isogenic lines of melon (Cucumis melo L.), carrying the Vat gene or not. All behavioural and chemical data indicated that this resistance is constitutive. EPG analysis clearly showed that access to phloem, although delayed by alterations in pathway activities, was not impaired in terms of frequency of access or initiation of feeding. The most striking feature was, however, a very reduced duration of ingestion from phloem of resistant plants, making this compartment one of the tissues where the effects of the Vat gene are unambiguously expressed. This was confirmed by clear differential activity of phloem extracts in artificial no-choice bioassays. Chemical analyses have shown that phloem saps from the two isogenic lines were extremely similar in profiles of ninhydrin positive compounds, and contained a low total amount of free amino acids (less than 10 mM). Out of more than 40 distinguishable peaks in the chromatograms (protein and non-protein amino acids, as well as small peptides), only five differentiated the two genotypes. Two of them were increased in the resistant genotype: glutamic acid and a major unknown peak, probably a non-protein amino acid (different from β pyrazolyl-alanine, a Cucumis-specific amino acid). The three others were depressed in resistant plants, and included the sulphur amino acid cystine and a peptide peak partly composed of the cysteine-containing peptide glutathione (reduced form). Sap collection also showed that phloem exudation rates, as well as total protein and glutathione levels, were depressed in phloem sap from resistant plants. Such data are all indicative of a modified phloem-sealing physiology, linked to sulfhydryl oxidation processes, in plants carrying the Vat gene. The originality of the mechanism of Vat resistance to aphids is discussed.

Potato plants (Solanum tuberosum) cv. Desiree were transformed with the genes encoding the proteins bean chitinase (BCH), snowdrop lectin (GNA) and wheat α-amylase inhibitor (WAI) under the control of the constitutive CaMV 35S promoter. Transgenic plants with detectable levels of foreign RNA were then selected for further characterisation with respect to protein expression levels by immunodot blot analysis using polyclonal antibodies raised against the respective protein. With the exception of WAI, plants expressing high levels of RNA, expressed correspondingly high levels of the foreign protein (1.5–2.0% of the total soluble protein). Although high levels of WAI mRNA were detected in some of the transformants, the protein could not be detected. On the bases of expression levels, two lines, designated PWG6#85 (transformed with the double construct WAI/GNA) and PBG6#47 (transformed with the double construct BCH/GNA), were selected for testing in aphid trials for enhanced levels of resistance. Both transgenic lines had a marked and significant effect on fecundity. The number of nymphs produced per female per day peaked at 4.1 and 4.2 for lines PBG6#47 and PWG6#85 respectively, compared to a value of 5.4 on control plants. Total nymphal production was also significantly lower on either of the transgenic lines compared to control plants (P

Three mannose-binding lectins were assayed in artificial diets for their toxic and growth-inhibitory effects on nymphal development of the peach-potato aphid Myzus persicae. The snowdrop (Galanthus nivalis) lectin GNA was the most toxic, with an induced nymphal mortality of 42% at 1500 μg ml -1 (30 μM) and an IC 50 (50% growth inhibition) of 630 μg ml -1 (13 μM). The daffodil (Narcissus pseudonarcissus) lectin NPA and a garlic (Allium sativum) lectin ASA induced no significant mortality in the range 10-1500 μg ml -1 , but did result in growth inhibition of 59% (NPA) and 26% (ASA) at 1500 μg ml -1 (40 μM for NPA, 63 μM for ASA). All three lectins were responsible for a slight but significant growth stimulation when ingested at 10 μg ml -1 , reaching + 26%, + 18% and + 11% over the control values for the garlic lectin, the daffodil lectin and the snowdrop lectin, respectively. GNA, as well as the glucose/mannose binding lectin Concanavalin A, were also provided at sublethal doses throughout the life cycle of the aphids, and effects on adult performance were monitored. Adult survival was not significantly altered, but both lectins adversely affected total fecundity and the dynamics of reproduction, resulting in significant reduction in calculated r m's (population intrinsic rate of natural increase) on lectin-containing diets. These effects are discussed in relation to the use of transgenic plants expressing these toxic lectins for potential control of aphid populations.

BGPI : équipe 6; International audience; Crop protection requires the accurate identification of disease vectors, a task that can be made difficult when these vectors encompass cryptic species. Here we developed a rapid molecular diagnostic test to identify individuals of Cacopsylla pruni (Scopoli, 1763) (Hemiptera: Psyllidae), the main vector of the European stone fruit yellows phytoplasma. This psyllid encompasses two highly divergent genetic groups that are morphologically similar and that are characterized by genotyping several microsatellite markers, a costly and time-consuming protocol. With the aim of developing species-specific PCR primers, we sequenced the Internal Transcribed Spacer 2 (ITS2) on a collection of C. pruni samples from France and other European countries. ITS2 sequences showed that the two genetic groups represent two highly divergent clades. This enabled us to develop specific primers for the assignment of individuals to either genetic group in a single PCR, based on ITS2 amplicon size. All previously assigned individuals yielded bands of expected sizes, and the PCR proved efficient on a larger sample of 799 individuals. Because none appeared heterozygous at the ITS2 locus (i.e., none produced two bands), we inferred that the genetic groups of C. pruni, whose distribution is partly sympatric, constitute biological species that have not exchanged genes for an extended period of time. Other psyllid species (Cacopsylla, Psylla, Triozidae and Aphalaridae) failed to yield any amplicon. These primers are therefore unlikely to produce false positives and allow rapid assignment of C. pruni individuals to either cryptic species.

The genetic diversity of three temperate fruit tree phytoplasmas ‘Candidatus Phytoplasma prunorum’, ‘Ca. P. mali’ and ‘Ca. P. pyri’ has been established by multilocus sequence analysis. Among the four genetic loci used, the genes imp and aceF distinguished 30 and 24 genotypes, respectively, and showed the highest variability. Percentage of substitution for imp ranged from 50 to 68 % according to species. Percentage of substitution varied between 9 and 12 % for aceF, whereas it was between 5 and 6 % for pnp and secY. In the case of ‘Ca P. prunorum’ the three most prevalent aceF genotypes were detected in both plants and insect vectors, confirming that the prevalent isolates are propagated by insects. The four isolates known to be hypo-virulent had the same aceF sequence, indicating a possible monophyletic origin. Haplotype network reconstructed by eBURST revealed that among the 34 haplotypes of ‘Ca. P. prunorum’, the four hypo-virulent isolates also grouped together in the same clade. Genotyping of some Spanish and Azerbaijanese ‘Ca. P. pyri’ isolates showed that they shared some alleles with ‘Ca. P. prunorum’, supporting for the first time to our knowledge, the existence of inter-species recombination between these two species.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Aphis gossypii and Bemisia tabaci are severe hemipteran pests of melon crops and breeding for resistance to both insects is required to reduce pesticide use. Resistance was evaluated for its effect on behaviour and biotic potential of both hemipterans in a population of recombinant inbred lines (RILs) derived from the cross Védrantais x PI 161375. Insect variability was considered using two A. gossypii clones and two B. tabaci populations. Two additive QTLs affected the whiteflies. Four additive QTLs and two couples of epistatic QTLs affected the aphids. Amongst them, a major QTL affects both behaviour and biotic potential of A. gossypii and therefore a same R gene induces both antixenosis and antibiosis. This major QTL colocalizes with the Vat gene belonging to the NBS-LRR gene family. No loci affected both aphids and whiteflies contrary to what was observed for the Mi1.2 gene, a NBSLRR gene in tomato. Original populations with different allelic compositions at QTLs affecting A. gossypii were built by one inter-crossing of RILs used for the mapping process. The genetic background was shown homogeneous between these populations what allowed validating QTLs and investigating the effect of allelic combinations at QTLs. Effects of QTLs were stronger than expected and some QTLs had a wider spectrum than expected. This strategy of validation appeared rapid and low cost.

UMR BGPI - Equipe 6; UMR CBGPPublication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Cacopsylla pruni is the vector of European stone fruit yellows, a quarantine disease of Prunus trees. Nine polymorphic microsatellite markers were developed from enriched DNA libraries. Allelic variability was assessed in a collection of 149 females obtained from five localities covering a large geographical area in France. The number of detected alleles ranged from 8 to 37. Within the localities, observed and expected heterozygosities averaged across loci ranged from 0.39 to 0.55, and from 0.68 to 0.81, respectively. A heterozygote deficiency was detected for almost all loci, possibly due to a high null allele frequency. Other possible causes of the homozygote excess (mode of reproduction, inbreeding, assortative mating or Wahlund effect) are discussed. These variable microsatellite loci can provide tools to assess overall genetic variation in this important vector species. They will be used to search for population structure and migration patterns of C. pruni.

UMR BGPI Equipe 6 ; UMR DAP Equipe DGBPublication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Understanding at which spatiotemporal scale a disease causes significant secondary spread has both theoretical and practical implications. We investigated this issue in the case of European stone fruit yellows (ESFY), a quarantine vector-borne phytoplasma disease of Prunus trees. Our work was focused on the processes underlying disease spread: the interplay between the life cycles of the pathogen ('Candidatus Phytoplasma prunorum') and of the vector (Cacopsylla pruni). We demonstrated experimentally that C. pruni has only one generation per year and we showed that, at least in southeastern France, C. pruni migrates between conifers in mountainous regions (where it overwinters) and Prunus spp. at lower altitude (where it breeds). In acquisition-inoculation experiments performed with C. pruni over its period of presence on Prunus spp., both immature and mature C. pruni were hardly infectious (0.6%) despite effective phytoplasma acquisition and multiplication. We demonstrated that most immature vectors born on infected plants reach their maximum phytoplasma load (107 genomes per insect) only after migrating to conifers and that, after a life-long retention of the phytoplasma, their transmission efficiency was very high (60%) at the end of winter (when they migrate back to their Prunus host). Thus, most transmissions occur only after an effective latency of 8 months, following vector migrations and overwintering on conifers in mountainous regions. From this transmission cycle, we can infer that local secondary spread of ESFY in apricot orchards is marginal, and recommend that disease management strategies take more into account the processes occurring at a regional scale, including the role of wild Prunus spp. in ESFY epidemics.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; European stone fruit yellows (ESFY) is becoming a major economic problem for Prunus growers in Europe. The causal agent ("Candidatus Phytoplasma prunorum") and its vector (Cacopsylla pruni) have been identified, but the present knowledge of the risk factors for this disease relies, at best, on specific experiments. To assess the relative significance of several factors correlated with ESFY incidence in the field, an exhaustive survey was performed on apricot and Japanese plum orchards in the Crau plain (France). After a preliminary multivariate exploration of the data, we used a logistic regression model to analyze and predict the cumulative number of diseased trees on the basis of a set of quantitative (age, planting density, and area of the orchard) and categorical variables (species, cultivar, and rootstock). Because of the nature of the data, we used an overdispersed binomial model and we developed a parametric bootstrap procedure based on the beta-binomial distribution to obtain confidence intervals. Our results indicated that the age, species, and cultivar of the scion were the major factors explaining the observed number of diseased trees. The planting density and the rootstocks used in the zone under study were less significant, and the area of the orchard had no effect. The residuals of the model showed that some explanatory variables had not been taken into account, because part of the remaining variability could be explained by a grower effect. The spatial distribution of the residuals suggested that one of the reasons for this grower effect was the correlation between orchards closer than 100 m, possibly caused by the flight behavior of infectious vectors.

International audience

International audience

Host plant resistance to pests is an important component of integrated control strategies. Due to the specialised phloem-feeding of aphids and many other hemipteran insect pests, which necessitates specific chemical treatments and control of virus transmission, this genetic strategy seems particularly attractive for this insect group. In the melon Cucumis melo L., a gene labelled vat, for virus aphid transmission (Pitrat & Lecoq, 1982), brings both a resistance to the melon aphid Aphis gossypii Glover and a resistance to the transmission by this vector of many non-persistent viruses. This gene induces both an antixenotic response to adults and an apparent antibiosis towards A. gossypii larvae. The purpose of the experiments reported here was to investigate the mechanisms of this resistance (mechanical, chemical, tissue localisation...) and to characterize any chemical difference between genotypes differing by the presence/absence of the vat gene.

The genetically closely related ‘Candidatus Phytoplasma mali’, ‘Candidatus Phytoplasma prunorum’ and ‘Candidatus Phytoplasma pyri’ are associated with economically important diseases such as apple proliferation, European stone fruit yellows and pear decline in European fruit tree areas and are spread by psyllid vectors of the superfamily Psylloidea (Hemiptera, Sternorrhyncha). Although the relationship between these phytoplasmas, their hosts and the vectoring psyllids is almost highly specific, there are some interconnections and biological factors which influence disease epidemiology and vector ecology and which should be taken into consideration for risk assessment and vector control. For a reliable risk assessment of a putative vector is important to know its population dynamics, its transmission efficiency, its host plant preferences and its epidemiological cycle. Although psyllid vectors usually show a high host plant specificity, being either monophagous or oligophagous on closely related plant species, shelter plants may serve as sources of inoculum and hence interfere with the disease spread. Therefore, the knowledge of the epidemiological cycle of both, the phytoplasma and its main vector is crucial for the development of efficient control measures.

Acute toxicity of thirty lectins was tested against the pea aphid Acyrthosiphon pisum (Harris) (Homoptera, Aphididae: Macrosiphini). Activity was measured on artificial diets containing moderate concentrations of lectins (10–250 μg/ml) by scoring mortality and growth inhibition over the whole nymphal period (7 days at 20°C). Most of the proteins tested exhibited low toxicity, but some induced significant mortality; these included the lectins from jackbean (Concanavalin A), amaranth, lentil and snowdrop. There was no direct correlation between toxicity and sugar specificity of the lectin; however, many mannose-binding lectins were toxic towards A. pisum. Concanavalin A was also tested on five other aphid species (Aphis gossypii, Aulacortum solani, Macrosiphum euphorbiae, Macrosiphum albifrons and Myzus persicae) at concentrations between 10–1500 μg/ml. Mortality was very variable from one species to another. Strong growth inhibition invariably occurred within this concentration range, although dose-response curves differed substantially between aphid species. The peptidase complement of A. pisum's digestive tract was also investigated, as well as the oral toxicity of some protease inhibitors (PIs) to this aphid. Most protein PIs were inactive, and no part of the digestive tract contained detectable amounts of endo-protease activity. This is in contrast to the strong amino-peptidase activity which was shown to occur predominantly in the midgut and crop portions of the digestive tract. The potential of lectins in transgenic crops to confer Host-Plant Resistance to aphids is discussed.

Bemisia tabaci (Gennadius) and Aphis gossypii Glover are devastating melon, Cucumis melo L., pests. The geographic areas where they occur overlap, and the same chemicals are used to control both of them. Therefore, to reduce pesticide use, it would be necessary to breed melon lines that simultaneously express a resistance to both insects. Female survival; the time when reproduction starts, peaks, and ends; the number of female offspring at the reproductive peak; and total reproduction (S) were determined under semicontrolled conditions for B. tabaci kept in clip-cages on a susceptible melon genotype Vedrantais, and 12 potential resistant accessions, particularly genotypes expressing the Vat gene controlling resistance to A. gossypii. By using the Lewontin triangular reproductive function and Bootstrapping, the intrinsic rate of increase (r) and its variance were calculated. Statistical analysis showed that the parameter S was as relevant as r for discriminating between the melon accessions. Three genotypes were potential genitors of resistance to the whitefly: PI 161375, PI 414723, and PI 532841. Those possessing the Vat gene were either resistant (PI 161375 and PI 414723) or susceptible (Margot, IsoVat R, and AR 5). This demonstrated the ineffectiveness of Vat against B. tabaci. In this article, we propose a strategy to breed lines that express resistance to aphids and whiteflies on the short-term.

Maladie du huanglongbing. Analyse du risque phytosanitaire pour l’Union européenne

International audience

Mannose-binding lectins were shown to be useful in creating transgenic plants resistant to insects, including many phloem-feeding Hemiptera. Before these plants can be used extensively, it is important to understand how these lectins exert their toxic effects on the target organisms. We investigated the feeding alterations induced by presenting the pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), with a diet containing the lectin from Canavalia ensiformis (ConA). A series of behavioural experiments were carried out to detect potential sensory mediation of lectin activity. Choice tests performed with a 400 μg ml -1 conA diet (3.7 μM of native tetramer) showed that A. pisum quickly rejected the ConA diet, but that this reaction was not typical of a sensory-mediated phagodeterrent effect. In addition, the aphids did not develop a conditioned taste aversion to the lectin. Diet uptake was evaluated using a radioactive tracer ( 14 C-methylated inulin), and showed depression of ingestion only after 16 h at 200 μg ml -1 or after 8 h at 400 μg ml -1 ConA. This effect was reversible under our test conditions. No evidence was obtained for early detection of the lectin, even by intoxicated aphids. An electrical penetration graph technique was adapted to artificial diets and provided short-term continuous analysis on feeding/probing events. At the 400 μg ml -1 level, adults were affected and had reduced ingestion durations as early as in the first 4 h of contact, but experienced an adaptation to the behavioural alterations induced by lectin feeding. Overall, feeding deterrency following exposure to mannose lectins appeared to be a consequence of intoxication, and not due to a sensory mediated process.

Master; The psyllid Cacopsylla pruni (Hemiptera: Psyllidae) is the only known vector of the pathogen ‘Candidatus Phytoplasma prunorum’, responsible for apricots and plum trees disease. Earlier studies hypothesised that C. pruni was a complex of two cryptic species, tentatively named A and B. However, this conclusion was based on the analyses on a limited number of populations from the south of France. A work published this year has provided a much more accurate picture of the ranges of the two groups across the Palearctic. Group A individuals are dominant in the Mediterranean region but they are also found central-western France and even further north near Paris. Group B individuals seems to be better adapted to the continental climate and are dominant in the east of France. They are in the majority or even in strict allopatry in central and eastern France, in Germany and as far as Turkey. In France, despite a large area of overlap in distribution, the two species hardly hybridise. This very strong reproductive barrier does not, however, rule out the existence of gene flow within each group, and thus the existence of subgroups or subspecies.The work presented in this study is based on the exploitation of a dataset covering a wider geographical area and closer to the distribution of psyllids known to date. Our study is based on the use of different types of markers (microsatellites, COI, ITS2) and the comparison of different analysis methods (multivariate analysis, clustering, haplotype networks). We confirm that there are two species within the C. pruni complex. However, our results show that each species has a different population structure. Species A seems to be homogeneously distributed over a large area covering south-eastern Spain and France, with the exception of the Massif Central, where no A individuals have been observed. Species B is distributed over the whole study area (from western France to Turkey) but seems to be subdivided into two or three genetic groups, between which gene flow is still visible (including between very distant populations), which could be a sign of an ongoing partition but too recent to lead to new species. We discuss the interest of these results in the context of an integrative taxonomy framework.; Le psylle Cacopsylla pruni (Hemiptera : Psyllidae) est un insecte vecteur de l’agent pathogène ‘Candidatus Phytoplasma prunorum’ responsable d’une maladie des abricotiers et des pruniers. Des études antérieures avaient émis l’hypothèse que C. pruni était en fait un complexe de deux espèces, provisoirement nommé A et B. Cependant, cette conclusion était basée sur l’analyse d’un nombre limité de populations du sud de la France. Or, des travaux publiés cette année ont permis d’avoir une vision beaucoup plus précise des aires de distribution des deux groupes à l’échelle du paléarctique. Les individus du groupe A sont prédominants dans la région méditerranéenne mais sont aussi retrouvés dans le centre ouest de la France, voire plus au nord dans la région parisienne. Les individus du groupe B semblent plus adaptés au climat continental. Ils sont majoritaires voire en allopatrie stricte dans le centre et l’est de la France, en Allemagne et jusqu’en Turquie. En France, malgré une large zone de chevauchement des aires de répartition, les deux espèces ne s’hybrident quasiment pas. Cette barrière reproductive très forte n’exclurait cependant pas l’existence de flux de gènes au sein de chaque groupe, et donc l’existence de sous-groupes ou sous-espèces.Les travaux présentés dans cette étude s’appuient sur l’exploitation d’un jeu de données couvrant une aire géographique plus étendue et plus proche de l’aire de répartition des psylles connue à ce jour. Notre étude repose sur l’exploitation de différents types de marqueurs (microsatellites, COI, ITS2) et la comparaison de différentes méthodes d’analyses (analyse multivarié, clustering, réseaux d’haplotypes). Nous confirmons qu’il existe deux espèces au sein du complexe C. pruni. Toutefois, nos résultats montrent que chaque espèce présente une structure des populations différente. L’espèce A semble se répartir de manière homogène à l’échelle d’un large territoire couvrant le sud-est de l’Espagne et la France, à l’exception du massif central, où aucun individu A n’a été observé. L’espèce B se répartit sur toute l’aire

The family Geminiviridae is the first group of plant viruses in terms of number and economic importance. They have circular single-stranded (css) DNA genomes and are transmitted in a circulative non-propagative (cnp) manner by leafhoppers, whiteflies, treehoppers and aphids (Hemiptera). While diseases induced by geminiviruses were reported for more than a century, aphid transmitted geminiviruses were discovered only recently by metagenomics. This delayed discovery is puzzling because aphids are the hemipterans that transmit the most plant viruses including the viruses of families Nanoviridae and Luteoviridae, transmitted in a cnp manner. Aphid transmission was detected among a group of 4 diverging geminiviruses exhibiting a typical genome organization and for which the genus Capulavirus was created. Aphid transmission was shown only for 2 of them, the Alfalfa leaf curl virus (ALCV) transmitted by Aphis craccivora and the Plantago latent virus (PlLV) transmitted by Dysaphis plantaginae. By demonstrating aphid transmission of a third capulavirus, Euphorbia caput-medusae latent virus (EcmLV), aphid transmission was validated as a generic taxonomic criterion. The population of A. craccivora that transmits EcmLV does not transmit ALCV, which reflect high transmission specificity among capulaviruses. ALCV was selected to investigate further geminivirus transmission by aphids because it was isolated on cultivated plants in France and associated with symptoms. Its localization in plant tissues (FISH) and the accurate analysis of the feeding behavior of the vector by electropenetrography (EPG) revealed that ALCV is phloem restricted and that its distribution is heterogeneous. Transmission tests and estimations of virus contents (qPCR) show that 12% of aphids, at maximum, transmit ALCV and that transmission is dependent on a critical threshold of virus content. We also show that ALCV accumulates and persist efficiently in the digestive tract of the vector aphid, with amounts that are similar to those of geminiviruses in their leafhopper of whitefly vectors. On the contrary, the amount and persistence of ALCV in hemolymph and heads are low, consistently with the low detection of ALCV by FISH in the salivary glands unlike in the digestive tract. These results may explain the low individual transmission rate of ALCV by A. craccivora, much lower than the 90% rate observed with geminiviruses transmitted by whiteflies and leafhoppers. Thanks to a broad bean nanovirus transmitted by A. craccivora, Faba bean necrotic stunt virus (FbNSV), we showed that the low transmission of ALCV is not imputable to the aphid. Indeed the comparisons carried out with the same A. craccivora population show that the transmission rate of FbNSV is 2 to 5 times higher than that of ALCV and FbNSV was excreted much more efficiently. FISH observations show that ALCV and FbNSV do not colocalize in midgut cells, which is consistent with distinct pathways. While nanoviruses and capulaviruses have both a circular single-stranded DNA genome, only nanoviruses encode a helper component for transmission (NSP). In geminiviruses, only CP is determining vector transmission. A yeast two-hybrid analysis carried out against the CP of ALCV identified three proteins of the digestive tract of A. craccivora. Their role in ALCV transmission will have to be validated with transmission and complementary interaction tests. Together with a similar study carried out in parallel by another Ph.D. student with the CP and the NSP of FbNSV, we expect to validate the hypothesis of distinct pathways with molecular data. The generalization of the low transmission efficiency of ALCV to all capulaviruses may explain both their late discovery and their preferential adaptation to perennial hosts. This hypothesis is discussed according to some rare descriptions of capulaviruses in natural conditions and in comparison with viruses of families Nanoviridae and Luteoviridae., Les virus de la famille Geminiviridae sont des virus à ADN simple brin circulaire (ADNsbc), transmis selon le mode circulant non-multipliant (snm) par cicadelle, aleurode, membracide et puceron (Hemiptera). Des maladies causées par des géminivirus sont décrites depuis plus d'un siècle, mais ce n'est que récemment que des geminivirus transmis par puceron ont été découverts. Cette découverte tardive est paradoxale car les pucerons sont les hémiptères qui transmettent le plus de virus de plante, y compris ceux des familles Nanoviridae et Luteoviridae, transmis selon le mode snm. La transmission par puceron a été détectée au sein d'un groupe de 4 géminivirus qui se distinguent par leurs séquences et organisations génomiques, et pour lesquels le genre Capulavirus a été créé. La transmission par puceron n'avait été démontrée que pour 2 d'entre eux, l'Alfalfa leaf curl virus (ALCV) transmis par Aphis craccivora et le Plantago latent virus (PlLV) par Dysaphis plantaginea. En démontrant la transmissibilité d'un 3e capulavirus par puceron, l'Euphorbia caput medusae latent virus (EcmLV), la transmission par puceron est validée comme critère taxonomique générique. La population de A. craccivora qui transmet l'EcmLV, ne transmet pas l'ALCV, ce qui témoigne d'une grande spécificité de transmission au sein des capulavirus. La circulation de l'ALCV a été suivi dans son puceron vecteur par des approches complémentaires. La localisation de l'ALCV dans les tissus de plante (FISH) et des analyses fines du comportement alimentaire du vecteur par électropénétrographie (EPG) montrent que l'ALCV est restreint au phloème et que sa distribution est hétérogène. Des tests de transmission et des mesures de teneurs virales (qPCR) montrent qu'au maximum 12% des pucerons transmettent l'ALCV et que la transmission est tributaire d'un seuil critique de teneur viral. Nous montrons aussi que l'ALCV s'accumule et persiste efficacement dans le tube digestif du puceron vecteur, comme d'autres géminivirus dans leurs vecteurs aleurode et cicadelle. Par contre, la teneur et la persistance de l'ALCV dans l'hémolymphe et dans la tête est faible, en cohérence avec les traces infimes d'ALCV détectées par FISH dans les glandes salivaires, contrairement au tube digestif. Ces résultats pourraient expliquer que le taux de transmission de l'ALCV par A craccivora est bien inférieur à celui de géminivirus transmis par aleurode ou cicadelle (90%). Grâce à un nanovirus de fève, le Faba bean necrotic stunt virus (FbNSV), nous avons vu que la faible transmission de l'ALCV n'est pas imputable au puceron. Avec une même population de A. craccivora, nous montrons que le taux de transmission du FbNSV est 2 à 5 fois plus élevé que celui de l'ALCV, et que le FbNSV est excrété beaucoup plus efficacement. Des observations en FISH montrent que l'ALCV et le FbNSV ne colocalisent pas dans les cellules de l'intestin moyen, suggérant des routes de circulation distinctes. Alors que dans les deux familles virales les génomes sont des ADNsbc, seuls les nanovirus ont une protéine assistante de la transmission (NSP). La transmission des géminivirus est déterminée uniquement par la CP. Un criblage double-hybride en levure contre la CP de l'ALCV a permis d'identifier 3 protéines du tube digestif de A. craccivora. Leur rôle dans la transmission devra être validé par des tests d'interaction complémentaires et de transmission. Un travail parallèle réalisé avec la CP et la NSP du FbNSV dans le cadre d'une autre thèse devrait permettre à terme de valider l'hypothèse de parcours propre à chaque virus sur une base moléculaire. La généralisation du faible taux de transmission de l'ALCV à l'ensemble des capulavirus pourrait expliquer à la fois leur découverte tardive, et leur adaptation préférentielle à des hôtes pérennes. Cette hypothèse est discutée par rapport à quelques observations de terrain et en comparaison avec des virus des familles Nanoviridae et Luteoviridae.

International audience; There is growing evidence that microorganisms are important ‘hidden players’ in insect–plant interactions. Insect symbionts can directly affect these interactions by providing insects with key nutrients or by interfering with the plant to modulate food provisioning to insects and plant defences. Insect symbionts can also have indirect cascading ecological consequences at the community level through insect- and plant-mediated effects that include their impact on insect reproduction, on natural enemies of herbivores or on plant-associated microorganisms. Identification of symbiotic communities associated with insects, characterization of transmission and acquisition patterns as well as understanding of molecular mechanisms underlying these plant–insect–microbe interactions have important ecological and evolutionary consequences. This review highlights the excitement that surrounds these investigations and the promise they hold for a better understanding of the functional, ecological and evolutionary impacts of symbionts on plant–insect interactions, with implications and relevance for both applied and fundamental researches.