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Lettuce cultivation under cover and/or in openfield is an economic interest in Pays de la Loire, France. However cryptogamic diseases and pest such as aphids are major constraint in market gardening production. In the current context of reducing the use of phytopharmaceutical products, soil pests are becoming a concern in market gardening. Alternative methods exist, but their partial and variable efficacity makes research and development of these methods against pests necessary for vegetable growers. In this study, plant extracts will be tested for their antifungal, biostimulant, anti-feeding, repellent and insecticidal properties.; La culture de la laitue sous abri et/ou en plein champ présente un intérêt économique en région des Pays de la Loire. Cependant, les maladies cryptogamiques ainsi que les ravageurs comme les pucerons constituent des contraintes majeures en production de cultures maraichères. Dans le contexte actuel de réduction de l’usage des produits phytopharmaceutiques, les bioagresseurs du sol deviennent préoccupants en maraîchage. Des méthodes alternatives existent, mais leurs efficacités partielles et variables rendent nécessaires la recherche et le développement sur ces méthodes contre ces bioagresseurs pour les maraichers. Dans cette étude, il sera question de tester des extraits végétaux en évaluant leur pouvoir antifongique, biostimulant, anti-appétant, répulsif et insecticide.

The combination of a companion plant with a cultivated plant is considered as an interesting strategy to reduce pest pressure and hence, the use of pesticides. Although several plants from the Alliaceae and Lamiaceae families are known to be efficient companion plants against aphid pests, only a few plants of the Geraniaceae family have been studied so far. The aim of this work was to investigate the potential effects of Geranium macrorrhizum as a companion plant on the colonization of sweet pepper (Capsicum annuum, Solanaceae) by the green peach aphid (Myzus persicae). Aphid’s feeding behavior, orientation behavior and life history traits were assessed on sweet pepper using EPG (ElectroPenetroGraphy), plant preference tests and clip-cage laboratory bioassays, respectively. They were compared in absence or presence of G. macrorrhizum whose leaves had been mechanically stimulated or not. This study revealed that G. macrorrhizum as a companion plant negatively impacted the feeding behavior, fecundity and survival rate of M. persicae on sweet pepper. The effects were exacerbated when G. macrorrhizum leaves were mechanically stimulated. However, G. macrorrhizum used as a companion plant does not impact M. persicae orientation. Our results bring new insights into the use of novel companion plants to regulate aphid pest populations.; La combinaison d'une plante compagne avec une plante cultivée est considérée comme une stratégie prometteuse pour réduire la pression des ravageurs et donc l'utilisation de pesticides. Bien que plusieurs plantes des familles des Alliaceae et des Lamiaceae soient connues pour être des plantes compagnes efficaces contre les pucerons ravageurs, seules quelques plantes de la famille des Geraniaceae ont été étudiées jusqu'à présent. Le but de ce travail était d'étudier les effets potentiels de Geranium macrorrhizum en tant que plante compagne sur la colonisation du poivron (Capsicum annuum, Solanaceae) par le puceron vert du pêcher (Myzus persicae). Le comportement alimentaire, le comportement d'orientation et les traits d’histoire de vie des pucerons ont été évalués sur le poivron en utilisant respectivement, l'EPG (ElectroPénétroGraphie), des tests de préférence de plantes et des suivis physiologiques en clip-cage. Ils ont été comparés en absence ou en présence de G. macrorrhizum dont les feuilles avaient été effleurées ou non. Cette étude a révélé que G. macrorrhizum en tant que plante compagne avait un impact négatif sur le comportement alimentaire, la fécondité et le taux de survie de M. persicae sur le poivron. Ces effets ont été exacerbés lorsque les feuilles de G. macrorrhizum ont été effleurées. Cependant, G. macrorrhizum utilisé comme plante compagne n'a pas d'impact sur l'orientation de M. persicae. Nos résultats apportent des perspectives novatrices sur l'utilisation de nouvelles plantes compagnes pour réguler les populations de pucerons ravageurs.

International audience; CRISPR-Cas9 technology is a very efficient functional analysis tool and has been developed in several insects to edit their genome through injection of eggs with guideRNAs targeting coding sequences of genes of interest. However, its implementation in aphids is more challenging. Aphids are major pests of crops worldwide thatalternate during their life cycle between clonality and sexual reproduction. The production of eggs after mating of sexual individuals is a single yearly event and isnecessarily triggered by a photoperiod decrease. Fertilized eggs then experience an obligate 3-month diapause period before hatching as new clonal colonies. Takinginto consideration these particularities, we developed in the pea aphid Acyrthosiphon pisum a step-by-step protocol of targeted mutagenesis based on the microinjectionwithin fertilized eggs of CRISPR-Cas9 components designed for the editing of a cuticular protein gene (stylin-01). This protocol includes the following steps:i) the photoperiod-triggered induction of sexual morphs (2 months), ii) the mating and egg collection step (2 weeks), iii) egg microinjection and melanization, iv) the3-month obligate diapause, v) the hatching of new lineages from injected eggs (2 weeks) and vi) the maintenance of stable lineages (2 weeks). Overall, this 7-monthlong procedure was applied to three different crosses in order to estimate the impact of the choice of the genetic combination on egg production dynamics by femalesas well as hatching rates after diapause. Mutation rates within eggs before diapause were estimated at 70–80%. The hatching rate of injected eggs following diapauseranged from 1 to 11% depending on the cross and finally a total of 17 stable lineages were obtained and maintained clonally. Out of these, 6 lineages were mutated atthe defined sgRNAs target sites within stylin-01 coding sequence, either at the two alleles (2 lineages) or at one allele (4 lineages). The final germline transmission rateof the mutations was thus around 35%. Our protocol of an efficient targeted mutagenesis opens the avenue for functional studies through genome editing in aphids.

Most plant viruses are transmitted by vectors and deciphering the virus-vector interactions is one of the keys to control the corresponding diseases. My PhD work focuses on the interaction between a virus of the family Nanoviridae, the species Faba bean necrotic stunt virus (FBNSV), and its aphid vectors. Nanoviruses have a multipartite genomic architecture, i.e. their genome is divided into several segments, each of which is individually encapsidated in a viral particle. Just like better-known luteo- and geminiviruses, nanoviruses are transmitted in a circulative non-propagative manner. This means that the virus crosses the intestinal barrier, transits into the hemolymph and passes into the salivary glands of the aphid without replication. It has previously been established that FBNSV requires a helper component (HC) for aphid transmission, and that this HC is the viral protein NSP.Using confocal microscopy, we established that the viral components involved in aphid-transmission (DNA, capsid protein (CP), and NSP) accumulate in the aphid midgut (AMG) and in specific cell types of the principal salivary glands (PSG). There, the 8 segments of FBNSV, the proteins CP and NSP transit together and accumulate within the same perinuclear cytoplasmic aggregates. We then further studied the subcellular pathway supporting the FBNSV transcytosis within aphids, using a wide range of techniques from confocal and electron microscopy to Yeast 2 Hybrid system. In collaboration with another PhD student of the group tackling similar questions on a geminivirus transmitted by aphids (ALCV), we could show that nano- and geminiviruses appear to follow distinct intracellular pathways within their common vector.It was previously known that some genome segments of nanoviruses can be omitted at inoculation without totally impairing systemic infection of host plants. We here demonstrate that vector transmission can reconstitute the full FBNSV genome from distinct plants, each infected with complementary incomplete sets of genome segments. The reconstitution can occur either within individual aphids acquiring segments sequentially, or within plants inoculated by distinct aphids carrying distinct FBNSV genome segments sets.Finally, this PhD work revealed for the first time that a HC (NSP) can function even when acquired days after the acquisition of virus particles. This original result opens new perspective on the mode of action of HCs, and we set these into the context of this research field in a review article.Key words : Nanovirus, FBNSV, aphid, transmission, helper factor, confocal microscopy.; Les virus de plantes sont majoritairement transmis par des insectes vecteurs. La compréhension de l’interaction entre les phytovirus et leurs vecteurs est l’une des clés pour le contrôle des maladies qu’ils causent. Les travaux de ma thèse portent sur l’interaction entre un virus appartenant à la famille Nanoviridae, l’espèce Faba bean nécrotic stunt virus (FBNSV) et ses pucerons vecteurs. Les nanovirus possèdent une architecture génomique multipartite c’est-à-dire que leur génome est divisé en plusieurs segments, chacun étant encapsidé individuellement dans une particule virale. Tout comme les lutéo- et geminivirus, les nanovirus sont transmis suivant le mode circulant non multipliant: le virus ingéré traverse la barrière intestinale, transite dans l’hémolymphe et passe dans les glandes salivaires du puceron sans aucune réplication. Il a été précédemment établi que la transmission du FBNSV, met en jeu un facteur assistant, la protéine virale NSP (Nuclear shuttle protein). A l’aide de la microscopie confocale, nous avons montré que les composants viraux nécessaires à la transmission (ADN, protéine de capside (CP) et NSP) s’accumulent dans les cellules de l’intestin moyen antérieur (AMG) et dans certaines cellules des glandes salivaires principales (PSG) du puceron. Les 8 segments du FBNSV, la CP ainsi que la NSP s’accumulent au sein des mêmes agrégats cytoplasmiques périnucléaires dans ces cellules. Nous avons alors étudié plus précisément ces agrégats, en recourant à différentes techniques, en particulier la microscopie confocale, la microscopie électronique et le double hybride, afin de mieux définir les voies de transport subcellulaire que le FBNSV emprunte. .En collaboration avec une étudiante en thèse dans l’équipe qui menait des travaux similaires sur un geminivirus (Alfalfa leaf curl virus) transmis par pucerons, nous avons pu démontrer que nano et geminivirus suivent des voies intracellulaires distinctes chez leur vecteur commun.Certains segments génomiques du FBNSV pouvant être omis lors de l’inoculation sans pour autant abolir l’infection systémique, nous avons démontré que la transmission par vecteur pouvait reconstituer des génomes complets à partir de différentes plantes infectées chacune par des génomes incomplets . La reconstitution des génomes complets peut avoir lieu soit au sein d’un seul individu vecteur, soit dans une nouvelle plante inoculée par deux individus vecteurs chacun apportant son lot de segments complémentaire.Enfin, ces travaux ont révélé pour la première fois, qu’un facteur assistant de la transmission peut assurer sa fonction même lorsqu’il est acquis plusieurs jours après les particules virales. Ce résultat original ouvre de nouvelles perspectives quant au mode d’action des facteurs assistants de la transmission par vecteur et nous les avons mises en contexte et discutées dans un article de synthèse portant sur ce domaines de rechercheMots-clés : Nanovirus, FBNSV, puceron, transmission, facteur assistant à la transmission, microscopie confocale.

Biodiversity loss affects the functioning of all ecosystems, including agroecosystems, through the loss of essential ecosystem services. Supporting populations of organisms providing those services though vegetation diversification schemes is a promising tool to maintain a high agricultural production as well as ecosystem health. Nevertheless, those schemes show contrasted and unexplained results. This work aims at understanding how increased cultivated diversity impacts pollinator and natural enemy community structure and functioning by considering interactions within and among those groups. Our results show a community shift in response to increased resource diversity, possibly leading to negative interactions. In aphid – parasitoid – hyperparasitoid trophic foodwebs, resource diversification seemed to increase hyperparasitism and competition among primary parasitoids, that could explain the limited aphid control. The intensive use of cultivated flowers by the domestic honeybee seemed to limit wild pollinator use of this resource. Moreover, we highlighted a decrease in aphid parasitism rate in response to high pollinator abundances, suggesting for the first time possible negative interactions among those groups. Rethinking agricultural landscapes considering resource use of each group at different spatio-temporal scales as well as interactions within and among groups is essential to optimize simultaneously several ecosystem services and reach more autonomous and resilient agricultural production., La crise de la biodiversité affecte le fonctionnement de tous les écosystèmes, notamment agricoles, via une perte des services écosystémiques. Favoriser les populations d’organismes à l’origine de ces services via des stratégies de diversification végétale est un levier prometteur pour maintenir une production agricole élevée ainsi que la santé des écosystèmes, mais les résultats obtenus sont variables et peu expliqués. L’objectif de cette thèse est de comprendre comment l’augmentation de la diversité cultivée impacte la structure et le fonctionnement des communautés de pollinisateurs et d’ennemis naturels en considérant leurs interactions. Nos résultats montrent que la diversification des ressources modifie la composition des communautés, pouvant mener à des interactions négatives. Dans les réseaux trophiques puceron – parasitoïde – hyperparasitoïde, la diversification semble avoir augmenté l’hyperparasitisme et la compétition entre les parasitoïdes primaires, ce qui expliquerait un contrôle des pucerons limité. L’utilisation massive des fleurs cultivées par les abeilles domestiques semble limiter l’utilisation de cette ressource par les pollinisateurs sauvages. De plus, nous avons observé une diminution du service de régulation des pucerons par les parasitoïdes en réponse à une forte abondance de pollinisateurs, signalant pour la première fois de possibles interactions négatives entre ces deux groupes. Optimiser plusieurs services écosystémiques simultanément demande de repenser les paysages agricoles en considérant l’utilisation des ressources de chaque groupe d’organismes à différentes échelles spatio-temporelles ainsi que les interactions au sein et entre ces groupes.

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.

Parasitoids are important natural enemies of aphids in wheat fields of northern China, and interest in them has increased in recent years. However, little is known regarding parasitoids of wheat aphids, which has hindered the study and understanding of aphid-parasitoid interactions. In the present study, three primary parasitoids and 15 hyperparasitoids were collected in wheat fields during a 2-year survey in northern China (2014, 2015) and a 2-year investigation at Langfang, Hebei Province (2015, 2016). Among them, Aphidius uzbekistanicus Luzhetski was found most frequently among the primary parasitoids, while Pachyneuron aphidis (Bouché) dominated the hyperparasitoid community. Investigation of the dynamics of wheat aphids and parasitoids revealed that the primary parasitoids appeared early in the growing period and that the hyperparasitoids appeared later. Analysis of the seasonal dynamics revealed that growth of the parasitoid population followed that of the aphid population and that the parasitism rates were highest in the late growing period.

International audience; Effector proteins play crucial roles in determining the outcome of various plant-parasite interactions. Aphids inject salivary effector proteins into plants to facilitate phloem feeding, but some proteins might trigger defense responses in certain plants. The pea aphid, Acyrthosiphon pisum, forms multiple biotypes, and each biotype is specialized to feed on a small number of closely related legume species. Interestingly, all the previously identified biotypes can feed on Vicia faba; hence, it serves as a universal host plant of A. pisum. We hypothesized that the salivary effector proteins have a key role in determining the compatibility between specific host species and A. pisum biotypes and that each biotype produces saliva containing a specific mixture of effector proteins due to differential expression of encoding genes. As the first step to address these hypotheses, we conducted two sets of RNA-seq experiments. RNA-seq analysis of dissected salivary glands (SGs) from reference alfalfa- and pea-specialized A. pisum lines revealed common and line-specific repertoires of candidate salivary effector genes. Based on the results, we created an extended catalogue of A. pisum salivary effector candidates. Next, we used aphid head samples, which contain SGs, to examine biotype-specific expression patterns of candidate salivary genes. RNA-seq analysis of head samples of alfalfa- and pea-specialized biotypes, each represented by three genetically distinct aphid lines reared on either a universal or specific host plant, showed that a majority of the candidate salivary effector genes was expressed in both biotypes at a similar level. Nonetheless, we identified small sets of genes that were differentially regulated in a biotype-specific manner. Little host plant effect (universal vs. specific) was observed on the expression of candidate salivary genes. Analysis of previously obtained genome re-sequenced data of the two biotypes revealed the copy number variations that might explain the differential expression of some candidate salivary genes. In addition, at least four candidate effector genes that were present in the alfalfa biotype but might not be encoded in the pea biotype were identified. This work sets the stage for future functional characterization of candidate genes potentially involved in the determination of plant specificity of pea aphid biotypes

Background: The Hemiptera (aphids, cicadas, and true bugs) are a key insect order, with high diversity for feeding ecology and excellent experimental tractability for molecular genetics. Building upon recent sequencing of hemipteran pests such as phloem-feeding aphids and blood-feeding bed bugs, we present the genome sequence and comparative analyses centered on the milkweed bug Oncopeltus fasciatus, a seed feeder of the family Lygaeidae. Results: The 926-Mb Oncopeltus genome is well represented by the current assembly and official gene set. We use our genomic and RNA-seq data not only to characterize the protein-coding gene repertoire and perform isoform-specific RNAi, but also to elucidate patterns of molecular evolution and physiology. We find ongoing, lineage-specific expansion and diversification of repressive C2H2 zinc finger proteins. The discovery of intron gain and turnover specific to the Hemiptera also prompted the evaluation of lineage and genome size as predictors of gene structure evolution. Furthermore, we identify enzymatic gains and losses that correlate with feeding biology, particularly for reductions associated with derived, fluid nutrition feeding. Conclusions: With the milkweed bug, we now have a critical mass of sequenced species for a hemimetabolous insect order and close outgroup to the Holometabola, substantially improving the diversity of insect genomics. We thereby define commonalities among the Hemiptera and delve into how hemipteran genomes reflect distinct feeding ecologies. Given Oncopeltus’s strength as an experimental model, these new sequence resources bolster the foundation for molecular research and highlight technical considerations for the analysis of medium-sized invertebrate genomes., La lista completa de autores puede verse en el archivo asociado., Facultad de Ciencias Exactas, Centro Regional de Estudios Genómicos

La lutte chimique préventive est encore aujourd’hui le principal moyen de lutte contre les bioagresseurs en culture de laitue d’hiver sous abri. Des stratégies alternatives ont été explorées dans le projet LILLA, visant soit à fournir des références expérimentales manquantes sur des techniques non chimiques de protection des plantes, soit à tester des conduites de cultures basées sur des stratégies intégrées de protection, limitant le recours aux pesticides. Des leviers innovants, comme une résistance génétique accrue aux agents de la pourriture du collet, ou la conduite de l’irrigation en goutte à goutte au lieu de l’aspersion, ont pu être identifiés. En considérant un ensemble de 23 essais comparatifs de conduite des cultures, une diminution de moitié du nombre de traitements fongicides en association avec des techniques alternatives ne montre pas une augmentation statistique du risque de perte de récolte. Contre les pucerons, les stratégies de contrôle biologique testées restent à améliorer. Le coût de mise en oeuvre des techniques alternatives est significatif mais, pour la plupart d’entre elles, reste modéré. Les plus efficaces de ces techniques pourraient plus facilement être mises en oeuvre dans les exploitations si les incertitudes sur les revenus de la récolte étaient moins grandes., Preventive chemical control is still today the main mean of managing pests in winter lettuce under shelter. Alternative strategies have been explored in the LILLA project, either to provide needed experimental results on non-chemical plant protection techniques, or to test cropping systems based on integrated protection strategies that reduce the use of pesticides. Innovative pest management levers, including increased genetic resistance to basal rots, or the use of drip instead of sprinkler-irrigation. Considering a set of 23 comparative crop management trials, halving the number of fungicide treatments in combination with alternative techniques does not show a statistical increase in the risk of crop failure. The biological control strategies tested against aphids remain to be improved. The cost of implementing alternative techniques is significant but remains moderate in most cases. The most effective of these techniques could be more easily implemented by farmers if uncertainties about crop income were lower.

Background The green peach aphids, Myzus persicae, are a predominant pest in peach orchards as they can alter fruiting and shoot development for several years. This aphid developed resistance against pesticides. Among the alternative control strategies is the reduction of the trees' attractiveness to aphids. In order to identify the plant variables related to plant susceptibility, young peach trees were submitted to various supplies of water and nitrogen, and then artificially infested with aphids. Shoot development, plant water potential and aphid abundance were then monitored on a weekly basis. The apex concentrations in total N, amino acids, soluble sugars and polyphenols were determined at infestation start and infestation peak. Results Until infestation peak, the thermal time requests for aphid development were independent of infestation severity. The aphid populations then collapsed more rapidly on the low infested shoots than on the high infested ones. Aphid abundances appeared to be positively related to shoot development (leaf expansion and secondary ramification), to shoot growth (stem length and diameter) and to apex concentrations in amino acids and non-structural carbohydrates (NSC). Polyphenols had the opposite effect. Conclusion Peach susceptibility to aphids depends on shoot development and apex composition, and could be lowered by decreasing the water and nitrogen inputs. © 2019 Society of Chemical Industry.

Le pêcher est affecté par de nombreux insectes phytophages parmi lesquels les pucerons. Ces insectes provoquent des dégâts très important. En raison du changement climatique, leur population augmente. Pour faire face à ces dégâts l’augmentation de l’utilisation des produits phytosanitaires ne cessent d’accroitre. Des moyens alternatifs peuvent être utilisés afin de réduire l’utilisation des pesticides pour protéger l’environnement. Les pratiques culturales peuvent contribuer au contrôle des bio-agresseurs en influant la croissance de la plante. L'objectif de notre étude est d'évaluer dans quelle mesure les pratiques de fertilisation et d'irrigation peuvent être optimisées sur des critères à la fois de production et de gestion de bio-agresseurs. Pour ce faire, des suivis de croissance et de l’état hydrique des arbres et des suivis d’infestation des pucerons ont été effectués. D’après les résultats obtenus, le traitement limité en eau et en azote retarde l’infestation des pucerons. Cependant, il semblerait qu’au niveau de l’arbre les traitements n’aient pas d’impact sur le nombre de feuilles et le nombre d’axes et de rosettes de la variété Ivoire en 2018 et 2019 mais peu d’effet sur la variété Conquise en 2018. De plus, la sévérité d’infestation semble dépendre de la croissance individuelle des rameaux en 2019. L’infestation des pucerons altère la photosynthèse en 2018 et 2019 et modifie la composition biochimique de l’apex et des fruits ainsi que la taille des fruits en 2018., The peach tree is affected by many phytophagous insects including aphids. These insects cause very significant damage. Due to climate change, their population is increasing. To cope with this damage, the increase in the use of phytosanitary products continues to increase. Alternative means can be used to reduce the use of pesticides to protect the environment. Cultural practices can help control bio-aggressors by influencing the growth of the plant. The objective of our study is to evaluate the extent to which fertilization and irrigation practices can be optimized on the criteria of both production and management of bio-aggressors. To do this, monitoring of growth and water status of trees and monitoring of infestation of aphids were carried out. Based on the results obtained, limited treatment with water and nitrogen delays the infestation of aphids. However, it appears that at the tree level the treatments have no impact on the number of leaves and the number of axes and rosettes of the Ivory variety in 2018 and 2019 but little effect on the variety Conquered in 2018. In addition, the severity of infestation appears to be dependent on individual twig growth in 2019. Aphid infestation impairs photosynthesis in 2018 and 2019 and modifies the biochemical composition of the apex and fruits as well as the size of the fruits in 2018.

International audience; Acibenzolar-S-methyl (ASM) is a chemical compound, which is able to induce resistance in several model and non-model plants, but the end-players of this induced defense remain ill-defined. Here, we test the hypothesis that treatment with ASM can protect apple (Malus × domestica) against the rosy apple aphid (Dysaphis plantaginea) and investigate the defense molecules potentially involved in resistance. We measured aphid life traits and performed behavioral assays to study the effect of ASM on plant resistance against the aphid, and then combined transcriptomic, bioinformatics, metabolic and biochemical analyses to identify the plant compounds involved in resistance. Plants treated with ASM negatively affected several life traits of the aphid and modified its feeding and host seeking behaviors. ASM treatment elicited up-regulation of terpene synthase genes in apple and led to the emission of (E,E)-α-farnesene, a sesquiterpene that was repellent to the aphid. Several genes encoding amaranthin-like lectins were also strongly up-regulated upon treatment and the corresponding proteins accumulated in leaves, petioles and stems. Our results link the production of specific apple proteins and metabolites to the antibiosis and antixenosis effects observed against Dysaphis plantaginea, providing insight into the mechanisms underlying ASM-induced herbivore resistance.

The aim of this PhD thesis is to develop innovative approaches to characterize host-microbiota relationships, and to apply them to finely explore the pea aphid microbiota using metagenomic data. Symbiotic relationships play a major role in the life and evolution of all organisms, but are imperfectly described, essentially because of the difficult characterization of the genomic diversity of the microbial partners. The rise of high throughput metagenomic sequencing is a game changer for the study of those systems, but also raises methodological issues to analyze large metagenomic datasets. Metagenomic is here applied to the pea aphid holobiont, a model system for the study of symbiotic relationships, sheltering a moderately complex microbial community. This level of complexity seems to be ideal to develop new approaches for the strain-resolved characterization of host-microbiota relationships. This thesis aims at a better description of this symbiotic community by distinguishing several scales of metagenomic diversity. In a first part, we present a framework for the metagenomic analysis of holobionts, relying first on the taxonomic assignation of reads by alignment to reference or newly assembled genomes, and then on the detection of genomic variants. Whole genome variant profiles make possible to track the evolutionary history of host-microbiota associations with a high resolution. In the case of the pea aphid, we highlight different scales and structures for the metagenomic diversity of the different symbionts, accounting for different transmission modes or evolutionary histories specific to each microbial partner. This framework is based on the availability of a suitable reference genome, that may be hard to obtain in a metagenomic context. In a second part, we therefore present a novel method for reference guided genome assembly from metagenomic data. This method is based on two steps. First, the recruitment and assembly of reads by mapping metagenomic reads on a distant reference genome, and second, the de novo assembly of the missing regions, allowed by the development of an improved version of the software MindTheGap. Compared to a standard metagenomic assembler, this methods makes possible to assemble a single genome in a reasonable time, and allows to detect eventual structural variations within the targeted genome. When applied to the pea aphid holobiont, MindTheGap yielded single contig assemblie of the obligatory symbiont Buchnera aphidicola, and helped to identify different structural variants of the bacteriophage APSE. This works paves the way to a finer characterization of host-microbiota interactions, and to the application of the presented approaches to more complex systems.; Ces travaux de thèse reposent sur le double objectif de proposer des approches innovantes pour l’étude des relations entre un hôte et son microbiote, et de les appliquer à la description fine de l’holobionte du puceron du pois par des données métagénomiques. Les relations symbiotiques façonnent le fonctionnement et l’évolution de tous les organismes, mais restent décrites de manière imparfaite, notamment à cause de la difficulté à caractériser la diversité génomique des partenaires microbiens constitutifs des holobiontes. L’essor des technologies de séquençage métagénomique révolutionne l’étude de ces systèmes, mais pose également des problèmes méthodologiques pour analyser les jeux de données métagénomiques. La métagénomique est ici appliquée au puceron du pois, un modèle d’étude des relations symbiotiques qui abrite une communauté bactérienne d’une complexité modérée, idéale pour développer de nouvelles approches de caractérisation de la diversité microbienne. Cette thèse vise à mieux décrire la communauté de symbiotes qu’abrite cet holobionte, notamment en distinguant les différents niveaux de variabilité génomique en son sein. Nous présentons une démarche pour l’analyse métagénomique d’holobiontes, qui repose d’abord sur l’assignation taxonomiques des lectures par alignement à des génomes de référence ou préalablement assemblés, puis sur la recherche de variants génomiques. L’étude de génotypes complets de symbiotes permet de retracer l’histoire évolutive des relations hôte-microbiote avec une résolution élevée. Chez le puceron du pois, nous mettons en évidence des niveaux et structures de diversité génomique différents selon les symbiotes, que nous proposons d’expliquer par les modalités de transmission ou l’histoire évolutive propre à chacun des partenaires microbiens. Cette approche repose sur la disponibilité d’un génome de référence adapté, qui est souvent difficile à obtenir en métagénomique. Dans un second temps, nous présentons donc une méthode d’assemblage guidé par référence en contexte métagénomique. Cette méthode se déroule en deux temps : le recrutement et l’assemblage de lectures par alignement sur un génome de référence distant, puis l’assemblage de novo ciblé des régions manquantes, permis par des développements complémentaires apportés au logiciel MindTheGap. Comparativement à un assembleur métagénomique, cette méthode permet l’assemblage d’un seul génome en un temps réduit, et permet de détecter d’éventuels variants structuraux sur le génome ciblé. Appliqué au puceron du pois, MindTheGap a réalisé l’assemblage du symbiote obligatoire Buchnera en un seul contig, et a permis d’identifier différents variants structuraux du bactériophage APSE. Ces travaux ouvrent la voie à la fois à une caractérisation plus précise des relations hôte-microbiote chez le puceron du pois par des approches fonctionnelles et métaboliques, ainsi qu’à l’application des outils présentés à des systèmes plus complexes.

Many plant viruses are transmitted in non-circulative manner by hemipteran vectors, often aphids. This transmission mode spreads viruses very quickly from one host to another and thereby causes countless damage on many crops of agronomic interest. Currently, the lack of knowledge about their transmission process is a hindrance to the development of effective control methods. Recently, results have shown that the model virus, Cauliflower mosaic virus (CaMV, genus Caulimovirus), responds to the arrival of aphid vectors by forming, at this time and reversibly, virus transmissible complexes, obligatory for the acquisition by the aphid. This extraordinary phenomenon called "transmission activation (TA)" controls the virus acquisition and thus its transmission. It’s a major discovery in non-circulative transmission and opens many research perspectives including expanding this phenomenon to other viruses to see if TA is a widespread phenomenon in the viruses propagation.Having this in mind, we are interested to study a virus unrelated to CaMV, Turnip mosaic virus (TuMV), a Potyvirus, also transmitted by aphids. The TuMV transmission depends on the direct interaction of the virus particle and the viral helper component protease (HC-Pro). Indeed, HC-Pro must form with the virus particle a transmissible complex, the only form of virus that can be acquired by the vector. Our results show that TuMV uses TA and that its TA depends on the presence of reactive oxygen species (ROS) and on calcium signaling. TuMV TA is correlated with the formation of HC-Pro disulfide bond mediated oligomers and the formation of HC-Pro transmissible complexes HC-Pro / viral particle in plant cells. Our pharmacological analysis showed that CaMV TA also depends on the presence of ROS and calcium signaling. These two signaling pathways are therefore involved presumably in the early stages of CaMV and TuMV TA. Experiments with other compounds have shown that the following steps of TA are different for the two viruses. A search for elicitors of the TA has been initiated but has not been successful yet.These results provide evidence of the existence of TA for a second genus of non-circulative virus, suggesting that this might be a general transmission mode. These new data open, from an applied point of view, new perspectives for control strategies, aimed at specifically interrupting the TA process.; Beaucoup de virus de plante sont transmis selon le mode non-circulant par vecteurs hémiptères, souvent des pucerons. Ce mode de propagation répand les virus très rapidement d’un hôte à l’autre, ce qui cause d’innombrables dégâts sur de nombreuses cultures d'intérêt agronomique. Actuellement, le manque de connaissances sur leur processus de transmission constitue un frein pour le développement de méthodes de lutte efficaces. Récemment, des résultats ont montré qu’un virus modèle, le Cauliflower mosaic virus (CaMV, genre Caulimovirus), répond à l'arrivée de son vecteur puceron en formant, à ce moment précis et de manière réversible, des complexes transmissibles du virus, obligatoire pour son acquisition par le puceron. Ce phénomène extraordinaire nommé « activation de la transmission (AT) » contrôle l’acquisition du virus et donc sa transmission. Il constitue une découverte majeure pour la transmission non-circulante et ouvre de nombreuses perspectives de recherche dont celle d’élargir ce phénomène à autres virus pour savoir si l’AT est un phénomène généralisé dans la propagation des virus.Dans cette optique, nous nous sommes intéressés à un virus non apparenté au CaMV, le Turnip mosaic virus (TuMV), un Potyvirus, également transmis par pucerons. La transmission du TuMV dépend de l’interaction directe de la particule virale et de la protéine virale facteur assistant de la transmission (HC-Pro). En effet, HC-Pro doit former avec la particule un complexe transmissible, seule forme du virus pouvant être acquis par le vecteur. Nos résultats montrent que le TuMV utilise l’AT et qu’elle est dépendante de la présence d’espèces réactives de l’oxygène (ROS) et de la signalisation calcique. L’AT du TuMV est corrélée avec la formation d’oligomères par ponts disulfures de HC-Pro et avec la formation des complexes transmissibles HC-Pro/particules virales dans les cellules végétales. Notre analyse pharmacologique a montré que l’AT du CaMV dépendait également de la présence des ROS et de la signalisation calcique. Ces deux voies de signalisation sont donc impliquées dans les étapes présumées précoces de l’AT du CaMV et du TuMV. Des expériences avec d’autres composés ont mis en évidence que les étapes suivantes de l’AT sont différentes pour les deux virus. Une recherche d’éliciteurs de l’AT a été initiée mais n’a pour l’instant pas permis d’en identifier un.Ces résultats ont mis en évidence l’existence de l’AT pour un deuxième genre de virus non-circulant, suggérant qu’il pourrait s’agir d’un mode de transmission général. Ces nouvelles données ouvrent, d’un point de vu appliqué, de nouvelles perspectives pour les stratégies de lutte, visant à interrompre spécifiquement le processus de l’AT.

The Vat gene in melon is unique in conferring resistance to both A. gossypii and the viruses it transmits. This double phenotype is controlled by a cluster of genes including a CC-NLR which has been characterized in detail. Copy-number polymorphisms (for the whole gene and for a domain that stands out in the LLR region) and single-nucleotide polymorphisms have been identified in the Vat cluster. The Vat gene structure suggests a functioning so called effector-triggered immunity (ETI), with separate recognition and response phases. During the recognition phase, the VAT protein is thought to interact (likely indirectly) with an aphid effector introduced by aphid salivation within the plant cells. A few hours later, several miRNAs are upregulated in Vat plants. Peroxidase activity increases, and callose and lignin are deposited in the walls of the cells adjacent to the stylet path, disturbing aphid behavior. In aphids feeding on Vat plants, the levels of miRNAs are modified. At the plant level, resistance to aphids is quantitative (aphids escape the plant and display low rates of reproduction). ‘Aphid-ETI’ has qualitative and local effect against non circulative viruses (CMV, ZYMV, WMV) and but quantitative effect against circulative virus such as CABYVs. Durability of ETI is highly variable. At population level, ‘Aphid-ETI’ reduces aphid density and genetic diversity, and durability of the ‘Aphid-ETI’ strongly depends on the agro-ecosystem. Some clones are adapted to Vat resistance, putatively either by introducing a polymorphic effector not triggering ETI, or by adapting to the defenses they triggered. Several ways to enhance ‘Aphid-ETI’ durability will be proposed. ‘Aphid-ETI’ against viruses decreases the intensity of Cucumber Mosaic Virus (CMV) and Cucurbit aphid-borne yellows virus (CABYV) epidemics. Laboratory experiments strongly suggested that non circulative viruses cannot adapt to ‘Aphid-ETI’ and therefore durability of ‘Aphid-ETI’ against CMV is predicted long. Field experiments combined to modelling suggested that highly durable resistance against CABYV could be obtained by combining within a same melon genotype the Vat gene with recessive genes conferring resistance to CABYV. Extension of those results to any other circulative viruses will be discussed.

In France, most of the territory occupied by agriculture belongs to arable crops, of which cereals represent the main production with more than 9 million hectares. Aphids are harmful pests in these crops causing direct and indirect damage and significant economic losses. Among alternative insecticide control methods for aphids, "natural regulation or conservational biological control" tends to stimulate the habitats where beneficial organisms are present in order to maintain them in agricultural plots. Farmers would need decision support tools to facilitate the implementation of measures that support these beneficial organisms. In this context, the goal of my internship is to characterize the aphid control service by their natural enemies, as well as to improve the existing DEXi multicriteria assessment tools. Thanks to the monitoring carried out by three different methods (visual observation, aspiration and yellow bowls) in the Rhône-Alpes region, it has been seen that the population dynamic of aphids follows similar trends in the different plots observed. Statistical approaches such as PCA and GLM highlight a spatial-temporal concordance between the presence of natural enemies and aphids. Nevertheless, the effect of other factors like climatic conditions, the state of the crop and the environment close to the plot are also important to take into account in this regulation and are still poorly defined. Further studies on these variables, as well as the auxiliary / pest ratio, would provide a better understanding of this natural regulation process.; En France, la plus grande partie des surfaces agricoles sont occupées par des grandes cultures qui sont impactées par divers ravageurs causant des dégâts directs et indirects et des pertes économiques importantes. Parmi ceux-ci les pucerons sont les ravageurs les plus redoutés. Concernant les méthodes alternatives aux insecticides vis-à-vis des pucerons, la « régulation naturelle ou le contrôle biologique par conservation » tend à rechercher des solutions pour favoriser les organismes auxiliaires au sein des parcelles agricoles. Les agriculteurs auraient besoin d’outils d’aide à la décision pour faciliter la mise en place de mesures favorables à ces auxiliaires. Dans ce contexte, la problématique de ce stage est de caractériser le service de régulation des pucerons par leur faune auxiliaire, ainsi que d’améliorer les outils d’aide à l’évaluation multicritère DEXi existants. Grâce aux suivis réalisés par trois méthodes différentes (observation visuelle, aspiration et cuvette jaune) en région Rhône-Alpes, il a été constaté que les populations de pucerons évoluent de manières similaires dans les différentes parcelles observées. Des approches statistiques de type ACP et GLM ont permis de mettre en évidence une concordance spatio-temporelle entre la présence des auxiliaires et des pucerons. Néanmoins, l’effet d’autres facteurs comme les conditions climatiques, l'état de la culture et l'environnement proche de la parcelle sont également importants à prendre en compte dans cette régulation et sont encore mal cernés. Des études complémentaires sur ces variables, ainsi que sur le ratio auxiliaire/ravageur, permettraient de mieux comprendre ce processus de régulation naturelle.

International audience; Effector proteins play crucial roles in plant-parasite interactions by suppressing plant defenses and hijacking plant physiological responses to facilitate parasite invasion and propagation. Although effector proteins have been characterized in many microbial plant pathogens, their nature and role in adaptation to host plants are largely unknown in insect herbivores. Aphids rely on salivary effector proteins injected into the host plants to promote phloem sap uptake. Therefore, gaining insight into the repertoire and evolution of aphid effectors is key to unveiling the mechanisms responsible for aphid virulence and host plant specialization. With this aim in mind, we assembled catalogues of putative effectors in the legume specialist aphid, Acyrthosiphon pisum, using transcriptomics and proteomics approaches. We identified 3,603 candidate effector genes predicted to be expressed in A. pisum salivary glands (SGs), and 740 of which displayed up-regulated expression in SGs in comparison to the alimentary tract. A search for orthologs in 17 arthropod genomes revealed that SG-up-regulated effector candidates of A. pisum are enriched in aphid-specific genes and tend to evolve faster compared with the whole gene set. We also found that a large fraction of proteins detected in the A. pisum saliva belonged to three gene families, of which certain members show evidence consistent with positive selection. Overall, this comprehensive analysis suggests that the large repertoire of effector candidates in A. pisum constitutes a source of novelties promoting plant adaptation to legumes.

This work aims to establish an ecologically integrated strategy for pest management to assess the impact of water and nitrogen depletion on Aphis pomi infestation in the Apple orchard.The results of the study of the impact on the green Apple aphid show a significant effect on the availability of water and nitrogen on the level of Aphis pomi infestation. Indeed, the normal fertigation regime (T1 = 100%) proved to be more favorable to a prominent development of aphids, in comparison with a 25% water and nitrogen deficit regime (T2 = 75%), that minimize infestation. As for the evolution of wingless aphid and green aphid with wing, the Aphis pomi, at both regimes, the general shape of the evolution of winged curves looks like the one of the wingless ones, with small differences. The number of leaves was higher in the T1 regime than that of T2. Moreover, the study of the orientation effect on the infestation of aphids has shown that the North andthe West sides were more infested than the East and the South ones. A negative effect on Syrphesp and ChrysoperlaCarnea densities was noticed under water and nitrogen depletion.

Objective Targeted sequencing of 16S rDNA amplicons is routinely used for microbial community profiling but this method suffers several limitations such as bias affinity of universal primers and short read size. Gene capture by hybridization represents a promising alternative. Here we used a metagenomic extract from the pea aphid Acyrthosiphon pisum to compare the performances of two widely used PCR primer pairs with DNA capture, based on solution hybrid selection. Results All methods produced an exhaustive description of the 8 bacterial taxa known to be present in this sample. In addition, the methods yielded similar quantitative results, with the number of reads strongly correlating with quantitative PCR controls. Both methods can thus be considered as qualitatively and quantitatively robust on such a sample with low microbial complexity. Electronic supplementary material The online version of this article (10.1186/s13104-018-3559-3) contains supplementary material, which is available to authorized users.

Les cultures associées sont définies comme la culture simultanée d’au moins deux espèces pendant une période significative de leur croissance et peuvent être vues comme une pratique agroécologique visant à « copier » la nature au service des hommes. Les travaux de Laurent Bedoussac se sont focalisés sur les associations entre une céréale (blé tendre ou blé dur) destinée à l’alimentation humaine et une légumineuse (pois ou féverole pour l’alimentation humaine et lentille ou pois chiche pour l’alimentation humaine). Dans ces exemples, les associations montrent de meilleures performances que les cultures pures en termes de rendement et de qualité en raison de processus écologiques dits de compétition, complémentarité et facilitation entre espèces notamment pour l’azote et la lumière. Toutefois, ces associations – qui sont récoltées en une fois – doivent ensuite être triées pour être valorisées en alimentation humaine afin de respecter les cahiers des charges des industriels ce qui pose un certain nombre de contraintes aux acteurs avals et en premier lieu aux coopératives. Dès lors diverses solutions doivent être envisagée avec les acteurs pour répondre aux contraintes et aux exigences de chacun nécessitant de mobiliser des approches multi-acteurs intégrant toute la filière et tous les acteurs en partant du champ jusqu’à l’assiette et c’est que Laurent Bedoussac cherchera à vous montrer.

Vection des bactéries par les insectes : la cuticule importe t’elle ?. 10. Réunion annuelle du Réseau de Biologie Adaptative des Pucerons et Organismes Associés : Bapoa

lien de la pièce jointe vers youtube : https://youtu.be/BDBAMaD-gKI; Les insectes ont souvent occupé une large place dans l'imaginaire collectif des sociétés humaines (abeille, scarabées, papillons).Mais les pucerons ?Sur la base de recherches non exhaustives dont la méthodologie sera exposée, nous proposerons un aperçu de la façon dont les artistes en tout genre et de tous siècles ont perçu les pucerons et leur place dans l'entourage humain.La période moderne étant pléthorique en images, nous essayerons de porter l'accent sur les périodes plus lointaines, de démêler une limite souvent floue entre l'art et la connaissance (connait-science), et de s'intéresser aux représentations non graphiques, les plus rares dans le corpus que nous avons exploré.Enfin, nous tenterons une analyse réflexive sur le regard que les artistes ont posé sur l'objet d'étude de notre communauté d'aphidologie: que cela nous dit il de nous, de nos animaux favoris, et des artistes, et donc des humains eux-mêmes...Vaste projet, que nous proposerons à une nouvelle section de la célèbre Encyclop'Aphid, pour l'occasion de sa translation dans la langue de Darwin...

International audience; A potential strategy for controlling pests is through the use of "companion plants" within a crop system. This strategy has been used in several trials to fight against a major crop insect pest: the aphid. We reviewed the literature to highlight the major mechanisms by which a companion plant may act. Trials carried out under laboratory or field conditions revealed that companion plants operate through several mechanisms. A companion plant may be associated with a target crop for various reasons. Firstly, it can attract aphids and draw them away from their host plants. Secondly, it can alter the recognition of the host plant. This effect is mostly attributed to companion plant volatiles since they disturb the aphid host plant location, and additionally they may react chemically and physiologically with the host plant, making it an unsuitable host for aphids. Thirdly, it can attract natural enemies by providing shelter and food resources. In this review, the feasibility of using companion plants is discussed. We conclude that many factors need to be taken into account for a successful companion plant strategy. For the best long-term results, companion plant strategies have to be combined with other alternative approaches against aphids.

SummaryVirtually all aphids maintain an obligate mutualistic symbiosis with bacteria from theBuchneragenus, which produce essential nutrients for their aphid hosts. Most aphids from the Lachninae subfamily have been consistently found to house additional endosymbionts, mainlySerratia symbiotica. This apparent dependence on secondary endosymbionts was proposed to have been triggered by the loss of the riboflavin biosynthetic capability byBuchnerain the Lachninae last common ancestor. However, an integral large-scale analysis of secondary endosymbionts in the Lachninae is still missing, hampering the interpretation of the evolutionary and genomic analyses of these endosymbionts. Here, we analysed the endosymbionts of selected representatives from seven different Lachninae genera and nineteen species, spanning four tribes, both by FISH (exploring the symbionts’ morphology and tissue tropism) and 16S rRNA gene sequencing. We demonstrate that all analysed aphids possess dual symbiotic systems, and while most harbourS. symbiotica, some have undergone symbiont replacement by other phylogenetically-distinct bacterial taxa. We found that these secondary associates display contrasting cell shapes and tissue tropism, and some appear to be lineage-specific. a scenario for symbiont establishment in the Lachninae, followed by changes in the symbiont’s tissue tropism and symbiont replacement events, thereby highlighting the extraordinary versatility of host-symbiont interactions.Originality-Significance StatementA key question in evolutionary biology is that of how mutualism evolves. One way to approach this problem is to investigate recently-established mutualistic associations, particularly by comparing various symbiotic systems in closely related hosts. Here, we present a most comprehensive study to investigate co-obligate symbioses in aphids, focusing in the Lachninae subfamily. While most aphids keep an obligate vertically-transmitted association with intracellularBuchnerabacteria, some, such as members of the Lachninae subfamily, host an additional putative co-obligate symbiont. Thus, the Lachninae dual symbiotic systems offer a unique opportunity to understand the evolutionary dynamics of host-symbiont associations, in particularly how secondary symbionts become obligate and eventually may be replaced. Through genome sequencing of three aphid species belonging to distantly related tribes within the subfamily, we have previously corroborated that they have indeed established co-obligate mutualistic associations with theS. symbioticasecondary endosymbiotic bacterium. This was putatively facilitated by an ancient pseudogenisation of the riboflavin biosynthetic pathway inBuchnera, rendering it unable to provide the essential vitamin to the host. However, not all Lachninae members harbourS. symbiotica, some species being associated to at least four different bacterial taxa. To correctly interpret the genomic data and to understand the evolutionary dynamics of these symbiotic associations, a wide-range analysis of both the phylogenetic relations as well as of the secondary symbionts’ localisation within the bacteriome is needed. To tackle this, we have combined phylogenetic analyses of the symbionts’ 16S rRNA gene sequences and FISH microscopy, to understand the symbiont’s identity as well as the morphological characteristics and tissue tropism. The phylogenetic affinities and patterns of co-divergence of the symbionts, in combination with previously published genomic data, have enabled us to build an evolutionary scenario for the establishment, changes in tissue tropism such as “stable” internalisation into bacteriocytes, and replacements of the putative “ancient” secondary endosymbiont from the Lachninae last common ancestor. Also, we were able to determine through phylogenetic analyses that some putative co-obligate endosymbionts may have evolved from once facultative ones. The evolutionary framework presented here reveals a dynamic pattern for the more recent evolutionary history of these symbioses, including replacement and novel acquisition of phylogenetically different co-obligate symbionts. This study opens new research avenues on this symbiont-diverse subfamily, providing insight into how mutualism in endosymbiotic associations can evolve, and the role these bacteria have played in the species’ adaptation and even in the speciation process.

Host-associated races of phytophagous insects provide a model for understanding how adaptation to a new environment can lead to reproductive isolation and speciation, ultimately enabling us to connect barriers to gene flow to adaptive causes of divergence. The pea aphid (Acyrthosiphon pisum) comprises host-races specialising on legume species, and provides a unique system for examining the early stages of diversification along a gradient of genetic and associated adaptive divergence. As host-choice produces assortative mating, understanding the underlying mechanisms of choice will contribute directly to understanding of speciation. As host-choice in the pea aphid is likely mediated by smell and taste, we use capture sequencing and SNP genotyping to test for the role of chemosensory genes in the divergence between eight host-plant species across the continuum of differentiation and sampled at multiple locations across western Europe. We show high differentiation of chemosensory loci relative to control loci in a broad set of pea aphid races and localities, using a model-free approach based on Principal Component analysis. Olfactory and gustatory receptors form the majority of highly differentiated genes, and include loci that were already identified as outliers in a previous study focusing on the three most closely related host races. Consistent indications that chemosensory genes may be good candidates for local adaptation and barriers to gene flow in the pea aphid open the way to further investigations aiming to understand their impact on gene flow, and to determine their precise functions in response to host plant metabolites. This article is protected by copyright. All rights reserved.

International audience; Increasing temperature and CO2 concentrations can alter tritrophic interactions in ecosystems, but the impact of increasingly severe drought on such interactions is not well understood. We examined the response of a wheat-aphid-parasitoid system to variation in water-deficit stress levels. Our results showed that arid area clones of the aphid, Sitobion avenae (Fabricius), tended to have longer developmental times compared to semiarid and moist area clones, and the development of S. avenae clones tended to be slower with increasing levels of water-deficit. Body sizes of S. avenae clones from all areas decreased with increasing water-deficit levels, indicating their declining adaptation potential under drought. Compared to arid area clones, moist area clones of S. avenae had a higher frequency of backing under severe water stress only, but a higher frequency of kicking under well-watered conditions only, suggesting a water-deficit level dependent pattern of resistance against the parasitoid, Aphidius gifuensis (Ashmead). The number of S. avenae individuals attacked by the parasitoid in 10 min showed a tendency to decrease with increasing water-deficit levels. Clones of S. avenae tended to have lower parasitism rates under treatments with higher water-deficit levels. The development of the parasitoid tended to be slower under higher levels of water-deficit stress. Thus, the bottom-up effects of water-deficit stressed plants were negative on S. avenae. However, the top-down effects via parasitoids were compromised by water-deficit, which could favor the growth of aphid populations. Overall, the first trophic level under water-deficit stress was shown to have an indirect and negative impact on the third trophic level parasitoid, suggesting that parasitoids could be increasingly vulnerable in future warming scenarios.

The impact of flower strips on the colonization of crops by the aphid Aphis gossypii and its natural enemies was studied from 2013 et 2015 within the framework of the AGATH project, funded by the Ministère de l’Agriculture, de l’Alimentation et de la Forêt (Casdar) and led by the Ctifl. A mix of flowers, tailored by the INRA (French National Institute for Agricultural Reasearch) to attract natural enemies of aphids in the proximity of melon crops without having a negative impact on the crops, was assessed in a network of plots throughout the three main melon production areas. The attractivity of this mix of flowers to natural enemies was characterized. The density of A. gossypii and of arthropod predator and/or parasitoid populations was compared in melon plots with these flower strips and in identical plots in terms of crop management but with bare soil.; L’effet de bandes fleuries sur la colonisation des cultures par le puceron Aphis gossypii et ses ennemis naturels a été étudié dans le cadre du projet AGATH, soutenu par le ministère de l’Agriculture, de l’Alimentation et de la Forêt (Casdar) et porté par le Ctifl de 2013 à 2015. Un mélange fleuri conçu par l’Inra pour attirer les ennemis naturels de pucerons à proximité des parcelles de melon sans exercer en parallèle d’effet délétère sur les cultures a été évalué dans un réseau de parcelles réparties dans les trois principaux bassins de production de melons. L’attractivité de ce mélange fleuri vis-à-vis des principaux ennemis naturels de pucerons a été caractérisée. Les densités des populations d’A. gossypii et d’arthropodes prédateurs et/ou parasitoïdes de pucerons mesurées dans des parcelles de melon bordées par ce mélange fleuri et dans des parcelles identiques en termes d’itinéraire technique mais bordées par une surface de sol nu ont été comparées.

The molecular mechanisms that allow generalist parasitoids to exploit many, often very distinct hosts are practically unknown. The waspAphidius ervi,a generalist koinobiont parasitoid of aphids, was introduced from Europe into Chile in the late 1970s to control agriculturally important aphid species. A recent study showed significant differences in host preference and host acceptance (infectivity) depending on the hostA. erviwere reared on. In contrast, no genetic differentiation betweenA. ervipopulations parasitizing different aphid species and aphids of the same species reared on different host plants was found in Chile. Additionally, the same study did not find any fitness effects inA. erviif offspring were reared on a different host as their mothers. Here, we determined the effect of aphid host species (Sitobion avenaeversusAcyrthosiphon pisumreared on two different host plants alfalfa and pea) on the transcriptome of adultA. ervifemales. We found a large number of differentially expressed genes (between host species: head: 2,765; body: 1,216; within the same aphid host species reared on different host plants: alfalfa versus pea: head 593; body 222). As expected, the transcriptomes from parasitoids reared on the same host species (pea aphid) but originating from different host plants (pea versus alfalfa) were more similar to each other than the transcriptomes of parasitoids reared on a different aphid host and host plant (head: 648 and 1,524 transcripts; body: 566 and 428 transcripts). We found several differentially expressed odorant binding proteins and olfactory receptor proteins in particular, when we compared parasitoids from different host species. Additionally, we found differentially expressed genes involved in neuronal growth and development as well as signaling pathways. These results point towards a significant rewiring of the transcriptome ofA. ervidepending on aphid-plant complex where parasitoids develop, even if different biotypes of a certain aphid host species (A. pisum) are reared on the same host plant. This difference seems to persist even after the different wasp populations were reared on the same aphid host in the laboratory for more than 50 generations. This indicates that either the imprinting process is very persistent or there is enough genetic/allelic variation betweenA. ervipopulations. The role of distinct molecular mechanisms is discussed in terms of the formation of host fidelity.

1 Companion plants (CPs) may affect the performance of pests on their hosts because of their potential to emit volatile organic compounds (VOCs) and their effectiveness depends not only on the species, but also on their arrangement in the crop system. 2 The present study aimed to evaluate the effect of intercropping rosemary, lavender or basil on the performance of Myzus persicae populations on sweet pepper plants (Capsicum annum) under greenhouse conditions. 3 In a first set of experiments, sweet pepper plants were neighboured by either one or two CPs. In another set of experiments, rosemary was tested at three distances (0.5, 1.5 and 2.5 m) from the host plant. 4 The first set of experiments showed similar patterns of aphid performance (i.e. number of females and nymphs) when a sweet pepper plant was surrounded by one or two companion plants. However, aphid performance was affected more when sweet pepper plants were intercropped with rosemary compared with lavender or basil. 5 The effect of the companion plant decreased significantly with distance. Rosemary was most effective at 0.5 m, although its effectiveness decreased at 1.5 m, becoming insignificant at 2.5 m. 6 The results suggest that a CP may be effective under greenhouse conditions provided that it is located near the target plant.

International audience; In aphids, clonal individuals can show distinct morphological traits in response to environmental cues. Such phenotypic plasticity cannot be studied with classical genetic model organisms such as [i]Caenorhabditis elegans[/i] or [i]Drosophila melanogaster[/i]. The genetic basis of this biological process remain unknown, as mutations affecting this process are not available in aphids. Here, we describe a protocol to treat third stage larvae with an alkylating mutagen, ethyl methanesulfonate (EMS), to generate random mutations within the [i]Acyrthosiphon pisum[/i] genome. We found that even low concentrations of EMS were toxic for two genotypes of [i]A. pisum[/i]. Mutagenesis efficiency was nevertheless assessed by estimating the occurrence of mutational events on the X chromosome. Indeed, any lethal mutation on the X-chromosome would kill males which are haploid on the X so that we used the proportion of males as an estimation of mutagenesis efficacy. We could assess a putative mutation rate of 0.4 per X-chromosome at 10 mM of EMS. We then applied this protocol to perform a small scale mutagenesis on parthenogenetic individuals, which were screened for defects in their ability to produce sexual individuals in response to photoperiod shortening. We found one mutant line showing a reproducible altered photoperiodic response with a reduced production of males and the appearance of aberrant winged males (wing atrophy, alteration of legs morphology). This mutation appeared to be stable since it could be transmitted over several generations of parthenogenetic individuals. To our knowledge, this study represents the first example of an EMS-generated aphid mutant.

International audience; The impact of a cultivar mixture within the rows including the cvs Melrouge (low susceptibility to scab) and Pitchounette (Rvi6 resistant) was assessed during 2008e2009 in an organic apple orchard located in Rhône Valley (Drôme, France), on three important pests and diseases: scab, powdery mildew and rosy apple aphid. In this area, the resistance of Rvi6 gene was effective since the orchard plantation in 2004. The impact of the cultivar mixture was assessed per se, but also associated with sanitation practices to decrease the primary inoculum of scab and mildew, and compared to disease development on pure stands of Melrouge. The cultivar mixture showed a good efficiency to decrease the scab incidence on leaves and fruits; a significant effect on scab severity was observed in 2009 for the cultivar mixture plus sanitation practices. Our data confirmed the different susceptibility levels of the two cultivars for powdery mildew. Against powdery mildew, a favourable effect of cultivar mixture, at the condition it is associated with sanitation, was observed in case of a moderate level of the disease (2008). For rosy apple aphid, a favourable effect of cultivar mixture was observed on Melrouge in 2008 when Pitchounette has a good resistance level. In the context of organic production, the impact of the cultivar mixture seemed favourable for the control of the three pests and diseases.

ARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) project ARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) projectARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) project; Peach green aphid and rosy aphids can develop resistance to insecticides. Alternative strategies are therefore required to control these major pests in commercial orchards. To identify the key plant variables which determine tree resistance and could be manipulated by usual cultural practices we submitted potted peach and apple trees to contrasted water and nitrogen inputs. The trees were then artificially infected and the infestation dynamic followed in line with shoot development and apex composition. The high infested shoots grew faster, developed more secondary ramifications and their apices had higher amino acid and soluble sugar concentrations than the low infested shoots. Moreover, aphids preferred trees having a small number of fast growing shoots to others, having the same number of leaves being distributed among a higher number of smaller shoots. Irrigation and fertilisation could thus be used to improve tree resistance to aphids since those techniques contribute to the control of shoot development and composition.

Host plant resistance is an essential mean of controlling virus epidemies in crops. Resistance to viruses in plant belongs to three major families, either recessive or dominant resistance genes, as weil as the antiviral defense system based on RNA silencing. Most NBS-LRR antiviral resistances are triggered by the recognition of the NBS-LRR protein and a virus protein, playing the raie of avirulence factor. The Vat resistance gene in melon is unique among the dominant resistance to virus genes. It is a CC-NBS-LRR gene, it is triggered by the recognition between an aphid avirulence factor, delivered in plant cells by Aphis gossypii puncturing, and the CC-NBS-LRR pratein produced by Vat plants. This resistance is efficient against unrelated viruses transmitted on the non persistent mode (Boualem et al., 2016). We investigated if the resistance to virus triggered by A. gossypii in Vat plants is systemic.

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International audience; Virtually all aphids (Aphididae) harbor Buchnera aphidicola as an obligate endosymbiont to compensate nutritional deficiencies arising from their phloem diet. Many species within the Lachninae subfamily seem to be consistently associated also with Serratia symbiotica We have previously shown that both Cinara (Cinara) cedri and Cinara (Cupressobium) tujafilina (Lachninae: Eulachnini tribe) have indeed established co-obligate associations with both Buchnera and S. symbiotica However, while Buchnera genomes of both Cinara species are similar, genome degradation differs greatly between the two S. symbiotica strains. To gain insight into the essentiality and degree of integration of S. symbiotica within the Lachninae, we sequenced the genome of both Buchnera and S. symbiotica endosymbionts from the distantly related aphid Tuberolachnus salignus (Lachninae: Tuberolachnini tribe). We found a striking level of similarity between the endosymbiotic system of this aphid and that of C. cedri In both aphid hosts, S. symbiotica possesses a highly reduced genome and is found exclusively intracellularly inside bacteriocytes. Interestingly, T. salignus' endosymbionts present the same tryptophan biosynthetic metabolic complementation as C. cedri's, which is not present in C. tujafilina's. Moreover, we corroborate the riboflavin-biosynthetic-role take-over/rescue by S. symbiotica in T. salignus, and therefore, provide further evidence for the previously proposed establishment of a secondary co-obligate endosymbiont in the common ancestor of the Lachninae aphids. Finally, we propose that the putative convergent split of the tryptophan biosynthetic role between Buchnera and S. symbiotica could be behind the establishment of S. symbiotica as an obligate intracellular symbiont and the triggering of further genome degradation.

National Natural Science Foundation of China 31330064 State Key Laboratory of Cotton Biology Open Fund of China CB2016A09; Top-down force is referred to arthropod pest management delivered by the organisms from higher trophic levels. In the context of prevalent adoption of transgenic Bt crops that produce insecticidal Cry proteins derived from Bacillus thuringiensis (Bt), it still remains elusive whether the top-down forces are affected by the insect-resistant traits that introduced into the Bt crops. We explored how Bt cotton affect the strength of top-down forces via arthropod natural enemies in regulating a non-target pest species, the cotton aphid Aphis gossypii Glover, using a comparative approach (i.e. Bt cotton vs. conventional cotton) under field conditions. To determine top-down forces, we manipulated predation/parasitism exposure of the aphid to their natural enemies using exclusion cages. We found that the aphid population growth was strongly suppressed by the dominant natural enemies including Coccinellids, spiders and Aphidiines parasitoids. Coccinellids, spiders and the assemblage of other arthropod natural enemies (mainly lacewings and Hemipteran bugs) are similarly abundant in both plots, but with the parasitoid mummies less abundant in Bt cotton plots compared to the conventional cotton plots. However, the lower abundance of parasitoids in Bt cotton plots alone did not translate into differential top-down control on A. gossypii populations compared to conventional ones. Overall, the top-down forces were equally strong in both plots. We conclude that transgenic Bt cotton does not disrupt the top-down forces regulating the cotton aphid in central China.

Background Aphids are serious pest on crops. By probing with their stylets, they interact with the plant, they vector viruses and when they reach the phloem they start a continuous ingestion. Many plant resistances to aphids have been identified, several have been deployed. However, some resistances breaking down have been observed. In the melon, a gene that confers resistance to aphids has been deployed in some melon-producing areas, and aphid colony development on Vat-carrying plants has been observed in certain agrosystems. The Vat gene is a NBS-LRR gene that confers resistance to the aphid species Aphis gossypii and exhibits the unusual characteristic of also conferring resistance to non-persistently transmitted viruses when they are inoculated by the aphid. Thus, we characterized patterns of resistance to aphid and virus using the aphid diversity and we investigated the mechanisms by which aphids and viruses may adapt to the Vat gene. Results Using a Vat-transgenic line built in a susceptible background, we described the Vat- spectrum of resistance to aphids, and resistance to viruses triggered by aphids using a set of six A. gossypii biotypes. Discrepancies between both resistance phenotypes revealed that aphid adaptation to Vat-mediated resistance does not occur only via avirulence factor alterations but also via adaptation to elicited defenses. In experiments conducted with three virus species serially inoculated by aphids from and to Vat plants, the viruses did not evolve to circumvent Vat-mediated resistance. We confirmed discrepancies between both resistance phenotypes by testing each aphid biotype with a set of thirteen melon accessions chosen to reflect the natural diversity of the melon. Inheritance studies revealed that patterns of resistance to virus triggered by aphids are controlled by different alleles at the Vat locus and at least another locus located at a short genetic distance. Therefore, resistance to viruses triggered by aphids is controlled by a gene cluster. Conclusions Under the Flor model, changes in the avirulence gene determine the ability of the pathogen to overcome the resistance conferred by a plant gene. The Vat gene belongs to a resistance gene family that fits this pest/pathogen–plant interaction, and we revealed an additional mechanism of aphid adaptation that potentially exists in other interactions between plants and pests or pathogens. Electronic supplementary material The online version of this article (doi:10.1186/s12870-016-0708-5) contains supplementary material, which is available to authorized users.

Since the 20th century, the sub-Antarctic islands have suffered an increasing number of biological invasions. Despite the large number of publications on this topic, there is a lack of knowledge on parasitism rates of invasive species and on the role of parasites and pathogens to regulate their populations. Six aphid species have been introduced in the archipelagos of Crozet (Ile de la Possession, 46° 25’ S–51° 51’ E) and Kerguelen (49° 21’ S–70° 13’ E). Five of these species were found infected by entomopathogenic fungi of the order Entomophthorales. All these fungal species are cosmopolitan. Conidiobolus obscurus and Entomophthora planchoniana were the most frequently observed on Ile de la Possession and in Archipel des Kerguelen, respectively. This is the first report of pathogenic fungi of aphids on the sub-Antarctic islands. We discuss these results in the light of our current knowledge of these insect pathogens. Their introduction by aphids surviving on plants during transportation is the most likely hypothesis to explain their presence on these remote islands. Keywords: Natural enemies; introduced species; biological invasion; colonization; Zygomycetes; parasitism. (Published: 8 July 2016) Citation: Polar Research 2016, 35 , 28765, http://dx.doi.org/10.3402/polar.v35.28765

National audience; Les clip-cages ont été décrites pour la première fois en 1957 et sont utilisées depuis par tous les laboratoires travaillant avec des pucerons. Différentes versions ont été créées par la suite, qui ont pour avantage d’être très bon marché car fabriquées manuellement. Leur principal inconvénient est d’être peu pratiques d’utilisation car elles ne tiennent pas bien en place et sont difficiles à nettoyer. L’AphiCell quant à elle est imprimée en 3D, se nettoie facilement à l’eau et le dépôt des pucerons à l’intérieur est facilité. L’utilisation de l’AphiCell évite la dispersion des pucerons sur la plante ou en dehors, ce qui facilite leur élimination par la suite et évite l’utilisation de pesticides. Enfin, le test d’efficacité que j’ai effectué montre que l’AphiCell n’entrave pas la transmission des virus par pucerons.

International audience; In social aphids of the genus Tuberaphis a cysteine protease gene of the family cathepsin B exhibits soldier-specific expression and intestinal protease production. The product is orally excreted and injected by soldier nymphs into natural enemies, thereby exerting an insecticidal activity. In an attempt to gain insights into when and how the novel venomous protease for the altruistic caste has evolved, we investigated the soldier-specific type (S-type) and nonspecific type (N-type) cathepsin B genes from social and nonsocial aphids. All the social aphids examined, representing the genera Tuberaphis, Astegopteryx, and Cerataphis, possessed both the S-type and N-type genes. Phylogenetically distant nonsocial aphids also possessed cathepsin B genes allied to the S-type and the N-type, indicating the evolutionary origin of these genes in the common ancestor of extant aphids. In Tuberaphis species the S-type genes exhibited significant soldier-specific expression and accelerated molecular evolution whereas the N-type genes did not. In Astegopteryx and Cerataphis species, meanwhile, both the S-type and N-type genes exhibited neither remarkable soldier-specific expression nor accelerated molecular evolution. These results suggest that the S-type gene acquired the soldier-specific expression and the venom function after divergence of the genus Tuberaphis. On the structural model of the S-type protease of Tuberaphis styraci the accelerated molecular evolution was associated with the molecular surface rather than the catalytic cleft, suggesting that the venom activity was probably acquired by relatively minor modifications on the molecular surface rather than by generation of a novel active site. In Cerataphis jamuritsu the S-type gene was, although containing a stop codon, structurally almost intact and still transcribed, suggesting recent pseudogenization of the gene copy and possible relevance to relaxed functional constraint in the highly multiplied protease gene family. On the basis of these results we suggest that the massive amplification in aphid cathepsin B genes might have predisposed the evolution of venomous protease in the social aphid lineage and argue that gene duplication, accelerated molecular evolution, and acquisition of novel gene function must have played considerable roles in the evolution of complex biological systems including insect sociality.

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