Nouveaux objectifs de l'unité ISP, INRAE de Nouzilly, sur les arthropodes parasites d'animaux

International audienceThe Joint Infectiology and Public Health Research Unit (UMR ISP) aims to combat infectious diseases in livestock and humans. Integrated into the "One Health" concept, it brings together teams specialized in infectious pathologies involving - viruses, bacteria, parasites at the interface between humans, animals and the environment. ISP thus offers expertise and innovative tools to prevent and cure diseases by limiting the use of xenobiotics. Among the pathogens studied within ISP, arthropods and in particular insects are of major and growing interest. These pests for humans, animals and crops, in addition to the direct damage they cause through their parasitic way of life, are also vectors of serious diseases such as malaria. Characterized by exceptional prolificacy and ability to disperse, they prove extremely difficult to combat. In addition, the development of resistance to practically all the active molecules available on the market requires the implementation of new control strategies. ISP and in particular the Multiresistance and Pathogenic Power of Nematodes (MPN) team focuses its research on the identification of new pharmaceutical targets in nematodes and arthropods (insects and mites). It recently strengthened its staff with the recruitment of a Research Officer, Fotini Koutroumpa, specialized in insects and in particular in the receptors (ion channels) involved in the chemoreception of insects. The remarkable diversity of ion channels (neural proteins), in physiological functions as diverse and essential for survival as locomotion, food intake, recognition of host and sexual partners, defecation and excretion/secretion of immunomodulators, places them as privileged targets to be explored in the development of alternative and effective control methods. The MPN team specializes in studying the specificity of the drug-ion channel couple with the aim of avoiding the development of resistance while promoting more effective long-term targeted treatments. Finally, the team's interest in the sensory system of parasites and their chemical ecology also opens up other perspectives for control, such as the design of new traps based on the senses (smell, vision, taste). Fotini Koutroumpa will be responsible for strengthening and perpetuating research activities on insects within the team and the unit as well as comparative studies between the different parasites (nematodes/arthropods) with the aim of developing strategies specific treatments that are more respectful of the environment

BIOLOGIE ET PHYLOGEOGRAPHIE DE MONOCHAMUS GALLOPROVINCIALIS (COLEOPTERA, CERAMBYCIDAE) VECTEUR DU NEMATODE DU PIN EN EUROPE

In Portugal where he has recently been introduced accidentally, the phytopathogenic invasive nematode Bursaphelenhus xylophilus is transported and transmitted to host trees (Pinus pinaster) by his indigenous vector Monochamus galloprovincialis. In order to evaluate the risks of invasion and propagation in France and in the rest of Europe, a detailed study on the biology and ecology of the vector M. galloprovincialis, was conducted in this country, in parallel with a study on the genetic and morphological variability of his populations and those of his sister species M. sutor. It was shown that M. galloprovincialis, present in every French forest land, has four larval instars that were described. Fecundity, larval instars' duration and longevity were measured. The existence of a diapause in the fourth larval instar was observed and had as result a synchronisation of the adults' emergence; a prolonged diapause seems to exist for a small section of the population. The larval development can be affected by various factors, as the breeding log dimensions. M. galloprovincialis showed a preference for Pinus sylvestris, but it can develop on other Pinus species as well namely P. pinaster, major host in the South West regions. It seems that climatic conditions have more important role in the distribution of this insect than the host tree. This was confirmed by the molecular study. Genetic and morphological proximity was evident by twelve polymorphic sites of the cytochrome oxydase I and four morphological characters, three of which correspond to male genitalia characters. The totality of the results demonstrated that a great number of factors favourable to the propagation of the nematode are gathered in France.Au Portugal où il a été récemment introduit accidentellement, le nématode phytopathogène invasif Bursaphelenhus xylophilus est véhiculé et transmis par son vecteur indigène Monochamus galloprovincialis aux arbres hôtes (Pinus pinaster). Pour estimer les risques d'invasion et de propagation en France et au reste de l'Europe, une étude approfondie de la biologie et de l'écologie du vecteur M. galloprovincialis,, a été menée dans ce pays, en parallèle avec une étude de la variabilité génétique et morphologique de ses populations et de celles de son espèce sœur M. sutor. Il a été montré que M. galloprovincialis, présent dans toutes les forêts françaises, possède quatre stades larvaires qui ont été décrits. La fécondité, la durée des stades larvaires et la longévité ont été mesurées. L'existence d'une diapause au quatrième stade larvaire a été observée, dont l'effet est une synchronisation des émergences d'adultes ; une diapause prolongée semble exister chez une faible fraction de la population. Le développement larvaire peut être affecté par divers facteurs, dont les dimensions du rondin d'élevage. M. galloprovincialis a montré une préférence pour Pinus sylvestris, mais il peut aussi bien se développer sur d'autres espèces de Pinus notamment P. pinaster, essence majoritairement attaquée dans les régions du Sud Ouest. Il s'est avéré que ce sont surtout les conditions climatiques et non l'essence hôte, qui jouent un rôle important dans la distribution de cet insecte, ce qui a été confirmé par l'étude moléculaire. La proximité génétique et morphologique des espèces M. galloprovincialis et M. sutor a été mise en évidence par douze sites polymorphes du gène de la cytochrome oxydase I et quatre caractères morphologiques dont trois correspondant à des caractères de génitalias mâles. L'ensemble des résultats a permis de conclure qu'un grand nombre de facteurs favorables à la propagation du nématode sont réunis en France

Shifts in sensory neuron identity parallel differences in pheromone preference in the European corn borer

Pheromone communication relies on highly specific signals sent and received between members of the same species. However, how pheromone specificity is determined in moth olfactory circuits remains unknown. Here we provide the first glimpse into the mechanism that generates this specificity in Ostrinia nubilalis. In Ostrinia nubilalis it was found that a single locus causes strain-specific, diametrically opposed preferences for a 2-component pheromone blend. Previously we found pheromone preference to be correlated with the strain and hybrid-specific relative antennal response to both pheromone components. This led to the current study, in which we detail the underlying mechanism of this differential response, through chemotopically mapping of the pheromone detection circuit in the antenna. We determined that both strains and their hybrids have swapped the neuronal identity of the pheromone-sensitive neurons co-housed within a single sensillum. Furthermore, neurons that mediate behavioral antagonism surprisingly co-express up to five pheromone receptors, mirroring the concordantly broad tuning to heterospecific pheromones. This appears as possible evolutionary adaptation that could prevent cross attraction to a range of heterospecific signals, while keeping the pheromone detection system to its simplest tripartite setup

Fecundity and larval development of Monochamus galloprovincialis (Coleoptera Cerambycidae) in experimental breeding

$\bullet$ The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal. $\bullet$ Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors. $\bullet$ Fecundity was high, with 138.2 eggs per female. $\bullet$ For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described. $\bullet$ Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals. $\bullet$ An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development. $\bullet$ Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs. $\bullet$ There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations.Fécondité et développement larvaire de Monochamus galloprovincialis (Coleoptera Cerambycidae) en élevage. $\bullet$ L'objectif de l'étude était de clarifier certaines caractéristique de base –fécondité, mortalité, développement) de Monochamus galloprovincialis, le vecteur de Bursaphelenchus xylophilus, agent du dépérissement des pins au Portugal. $\bullet$ Durant deux ans, des expériences d'accouplement et de ponte ont été conduites sur rondins de P. sylvestris au laboratoire. Le développement larvaire a été suivi en extérieur. $\bullet$ La fécondité a été élevée, avec 138.2 œufs par femelle. $\bullet$ Pour la première fois chez M. galloprovincialis, le nombre de stades larvaires (4) de M. galloprovincialis a été défini et ceux-ci ont été décrits. $\bullet$ Des informations sont fournies sur la forme et la taille des galleries larvaires. Le forage des galeries dans l'aubier et le bois de cœur commence au troisième stade. Tous les stades peuvent hiverner mais les adultes émergent simultanément, ce qui conduit à un cycle annuel pour la plupart des individus. $\bullet$ Une diapause obligatoire intervient au quatrième stade. Cependant, 8.1 % des insectes ont un développement sur deux ans. $\bullet$ Des différences importantes ont été notes entre les deux années d'étude. Elles pourraient s'expliquer par la taille différente des rondins d'élevage. $\bullet$ Il existe une proximité biologique élevée entre les populations françaises de M. galloprovincialis et celles du Portugal et d'Europe de Nord. Cependant, une fécondité et une longévité plus élevées, ainsi qu'une proportion plus haute d'insectes ayant un développement sur deux ans, ont été observées en France par rapport aux populations portugaises

Présence de Bursaphelenchus mucronatus (Nematoda ; Aphelenchoididae) en France et association avec Monochamus galloprovin-cialis (Coleptera : Cerambycidae)

International audienceAs a consequence of the recent introduction of the pine wood nematode Bursaphelenchus xylophilus in Portugal, nematodes of the genus Bursaphelenchus were looked for in various French pine forests, in trees attacked by Monochamus galloprovincialis, the vector insect of B. xylophilus, and in the insects themselves. Trap trees were felled in 12 localities distributed all over the country. Nematodes were extracted from transversal stem discs; insects emerging from the trap trees were studied. B. hellenicus, B. leoni, B. mucronatus and B. sexdentati were isolated, but not B. xylophilus. The presence of B. mucronatus and the absence of B. xylophilus were confirmed by molecular markers. B. mucronatus was isolated from several regions with an average prevalence of 19%. The infestation of M. galloprovincialis by B. mucronatus reached 26.7%. The wide distribution of B. mucronatus in France could have an effect on the extension of B. xylophilus in a case of an introduction.Suite à la récente introduction du nématode du pin Bursaphelenchus xylophilus, au Portugal, les nématodes du genre Bursaphelenchus ont été recherchés dans diverses forêts de pins françaises, sur les arbres attaqués par Monochamus galloprovincialis, le vecteur de B. xylophilus, et sur les insectes eux-mêmes. Des arbres pièges ont été abattus dans 12 localités réparties sur le territoire national. Les nématodes ont été extraits de sections transversales de tronc, et les insectes émergeant des arbres pièges ont été étudié. B. hellenicus, B. leoni, B. mucronatus et B. sexdentati ont été isolés, mais pas B. xylophilus. La présence de B. mucronatus et l’absence de B. xylophilus ont été confirmées par des marqueurs moléculaires. B. mucronatus a été isolé de plusieurs régions avec une fréquence moyenne de 19 %. Le taux de contamination de M. galloprovincialis par B. mucronatus atteignait 26,7 %. La vaste distribution de B. mucronatus en France pourrait avoir un effet sur la propagation de B. xylophilus dans le cas d’une introduction accidentelle

Spodoptera littoralis genome mining brings insights on the dynamic of expansion of gustatory receptors in polyphagous noctuidae

International audienceThe bitter taste, triggered via gustatory receptors, serves as an important natural defense against the ingestion of poisonous foods in animals, and the increased host breadth is usually linked to an increase in the number of gustatory receptor genes. This has been especially observed in polyphagous insect species, such as noctuid species from the Spodoptera genus. However, the dynamic and physical mechanisms leading to these gene expansions and the evolutionary pressures behind them remain elusive. Among major drivers of genome dynamics are the transposable elements but, surprisingly, their potential role in insect gustatory receptor expansion has not been considered yet. In this work, we hypothesized that transposable elements and possibly positive selection would be involved in the highly dynamic evolution of gustatory receptor in Spodoptera spp. We first sequenced de novo the full 465 Mb genome of S. littoralis, and manually annotated the main chemosensory genes, including a large repertoire of 373 gustatory receptor genes (including 19 pseudogenes). We also improved the completeness of S. frugiperda and S. litura gustatory receptor gene repertoires. Then, we annotated transposable elements and revealed that a particular category of class I retrotransposons, the SINE transposons, was significantly enriched in the vicinity of gustatory receptor gene clusters, suggesting a transposon-mediated mechanism for the formation of these clusters. Selection pressure analyses indicated that positive selection within the gustatory receptor gene family is cryptic, only 7 receptors being identified as positively selected. Altogether, our data provide a new good quality Spodoptera genome, pinpoint interesting gustatory receptor candidates for further functional studies and bring valuable genomic information on the mechanisms of gustatory receptor expansions in polyphagous insect species