A PCR-based method for estimating parasitism rates in the olive fly parasitoids Psyttalia concolor and P. lounsburyi (Hymenoptera: Braconidae)

International audienceSeveral parasitoids of the genus Psyttalia have been repeatedly introduced as biological control agents against the principal pest of olive, the fly Bactrocera oleae. However, few of the parasitoids released have become established and proved effective against B. oleae. It may however still be possible to find effective biological control agents adapted to local environmental conditions among the highly diverse Psyttalia species and populations infesting B. oleae worldwide. For this purpose, we have developed a rapid, sensitive molecular method based on the polymerase chain reaction (PCR) for estimating and comparing the parasitism success of Psyttalia parasitoids through the detection of eggs and larvae within the host. This method was tested and shown to be appropriate for two Psyttalia species (Psyttalia concolor and Psyttalia lounsburyi). The possible detection of DNA was also demonstrated for several populations of these species and for other Psyttalia species, namely Psyttalia humilis and Psyttalia ponerophaga. For P. concolor and P. lounsburyi, a strong correlation was observed between the parasitism rates estimated by PCR, host larva dissection and counts of emerging parasitoids. No significant difference was found between the rates of parasitism estimated by host larva dissection and PCR, whereas the rates of parasitism estimated by PCR were significantly higher than those estimated from emergence, suggesting occurrence of mortality during the parasitoid development. This PCR method is thus highly reliable and provides an objective criterion for estimating the efficacy of biological control agent candidates from diverse taxa and populations of Psyttalia. ⇑ Corresponding author

Adverse effects of Bacillus thuringiensis bioinsecticide on non-target Drosophila species 1

Biopesticides based on Bacillus thuringiensis kurstaki (Btk) and israelensis (Bti) spores and toxins are widely used to control insect pests, increasing environmental risks to non-target biodiversity. Here, we tested for potential effects of larval ingestion of Bt commercial formulations on Drosophila species. Doses equivalent to those recommended for field application (⩽10^6 CFU/g of fly medium) had no effect whereas Btk doses 10 to 100-fold higher (10^7-10^8 CFU/g) altered the development (decreased emergence due to larval mortality and increased development time), and moderately influenced adult fitness-related traits. At the highest Btk and Bti dose (10^9 CFU/g), all larvae died before pupation. The impact of Btk formulations resulted from the spores/cleaved toxins synergy, but also additives. While recommended doses had no effect on non-target Drosophila species, the accumulation of Bt bioinsecticides in the environment could have adverse side-effects on the populations of these species and therefore their associated communities

Variation intra spécifique de résistance et de virulence dans un système hôte-parasitoïde (approche intégrative de la spécificité des interactions)

This thesis focuses on variations in parasitoid virulence and host resistance that explain variations in outcome in the Leptopilina boulardi-Drosophila yakuba system. Two parasitoid lines, having opposite virulence abilities against D. yakuba, have been compared for host selection behaviour and virulent strategies. Results suggest the existence of a relationship between virulence properties and host selection behaviour in L. boulardi. Besides, they demonstrate that different virulence strategies can be found in a parasitoid species. The physiological effects of parasitism on host immunity are described and the nature of virulence factors is analysed. The genetic and physiological bases of resistance are also considered, using two host lines respectively susceptible and resistant to this parasitoid. These data have been compared with those available in the L. bouladi-D. melanogaster model in order to discuss host specificity in parasitoids at the physiological and molecular level.Cette thèse porte sur les variations de virulence du parasitoïde et de résistance de l'hôte à l'origine de variation dans l'issue du parasitisme dans le modèle Leptopilina boulardi-Drosophila yakuba. Deux lignes du parasitoïde présentant des capacités de virulence contrastées ont été comparées pour leur comportement de sélection d'hôte et leur stratégie de virulence. Les résultats obtenus suggèrent une relation entre virulence et comportement de choix d'hôte et démontrent l'existence de différentes stratégies parasitaires chez une espèce parasitoïde. Les effets physiologiques de la variation de résistance ont été étudiées chez deux lignées hôtes, sensible et résistante. Ces données ont été comparées avec celles disponibles dans le modèle L. boulardi-D. melanogaster afini d'aborder la spécificité parasitaire au niveau physiologique et moléculaire.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

Les facteurs immunosuppresseurs dans le système hôte-parasitoïde Leptopilina boulardi-Drosophila melanogaster

Le travail décrit les facteurs de virulence de Leptopilina boulardi, parasitoïde de Drosophila melanogaster . La souche virulente contourne les défenses immunitaires de l'hôte . La souche avirulente est encapsulée par l'hôte . Les femelles L.boulardi injectent des facteurs sécrétés dans la glande impaire qui confèrent une protection active aux oeufs . Quatre bandes protéiques majeures sont présentes dans la glande impaire de la souche virulente . L'une d'elles, P4 (35kDa), a un effet immunosuppresseur majeur . Elle est responsable d'une altération de la forme des lamellocytes(cellules impliquées dans la constitution de la capsule)de la larve hôte . L'ADNc de P4 code une protéïne ayant un domaine Rho-GAP(protéïnes impliquées dans la régulation du cytosquelette), ce qui explique l'effet de P4 sur la forme des lamellocytes . La protéïne est localisée au niveau des VLPs(Virus-Like Particles) des glandes de la souche virulente, montrant que les VLPs sont impliquées dans la réussite parasitaire.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

Virus-like particles in parasitoids' venom: viral or cellular origin ?: Virus-like particles, venom, wasps, Leptopilina, Drosophila

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Aphid infestation differently affects the defences of nitrate-fed and nitrogen-fixing Medicago truncatula and alters symbiotic nitrogen fixation

International audienceLegumes can meet their nitrogen requirements through root nodule symbiosis, which could also trigger plant systemic resistance against pests. The pea aphid , a legume pest, can harbour different facultative symbionts (FS) influencing various traits of their hosts. It is therefore worth determining if and how the symbionts of the plant and the aphid modulate their interaction. We used different pea aphid lines without FS or with a single one (, ) to infest plants inoculated with (symbiotic nitrogen fixation, SNF) or supplemented with nitrate (non-inoculated, NI). The growth of SNF and NI plants was reduced by aphid infestation, while aphid weight (but not survival) was lowered on SNF compared to NI plants. Aphids strongly affected the plant nitrogen fixation depending on their symbiotic status, suggesting indirect relationships between aphid- and plant-associated microbes. Finally, all aphid lines triggered expression of () and , respective markers for salicylic and jasmonic pathways, in SNF plants, compared to only in NI plants. We demonstrate that the plant symbiotic status influences plant-aphid interactions while that of the aphid can modulate the amplitude of the plant's defence response

L’invasion mondiale de Drosophia suzukii : le fait d’être le « cousin » d’un organisme-modèle aide-t-il réellement à établir un contrôle biologique ? Espoirs, désillusions et nouvelles perspectives

Article sous presseInternational audienceThe recent and rapid invasion of Europe and North-America by Drosophila suzukii has generated numerous laboratory and field studies since this fly species is an agricultural pest that causes economical losses by laying eggs and developing in ripening fruits, but also because of its relatedness with the model species Drosophila melanogaster whose biology and genetics are well described. This commentary is based on recent data published by different research groups as well as some of our own preliminary results. It discusses the state of research on D. suzukii and addresses the main following questions: can the wide knowledge on D. melanogaster help us to understand and manage the D. suzukii invasion and how? Are lab results on D. suzukii really informative on its biology? How can the ecological impact of an invasive species be evaluated if the ecological niche is poorly described in terms of biodiversity and trophic network? We also outline constraints for the biological control of this pest species and suggest new possible approaches for its long-term management.L’invasion récente et rapide de Drosophila suzukii en Europe et en Amérique du Nord a suscité de nombreuses études sur le terrain comme en laboratoire. Cette drosophile est en effet à la fois un ravageur important, du fait de son développement dans des fruits à maturité, et une « cousine » de l’espèce modèle Drosophila melanogaster dont la biologie et la génétique sont bien connues. Cet article s’appuie sur les données publiées par différentes équipes et sur des résultats préliminaires pour discuter de l’avancée des recherches et notamment des questions suivantes: en quoi nos connaissances sur D. melanogaster peuvent-elles ou non aider à comprendre et gérer l’invasion de D. suzukii ? Les résultats obtenus en condition de laboratoire avec cette espèce sont-ils représentatifs de sa biologie ? Comment mesurer l’impact écologique d’une espèce invasive si la niche qu’elle vient occuper est peu décrite localement en termes d’espèces présentes et de réseaux trophiques ? Cet article discute aussi des pistes et contraintes en termes de lutte biologique et de biocontrôle

Field monitoring of <em>Drosophila suzukii</em> and associated communities in south eastern france as a Pre-requisite for classical biological control

International audienceThe spotted wing Drosophila, Drosophila suzukii (Ds), became a major economic pest for fruit production since its establishment in Europe and America. Among potential control methods, only classical biological control appears to be a mean of sustainably regulating Ds in both cultivated and natural habitats. In the frame of risk assessment, pre-release surveys were carried out in a restricted but highly heterogeneous area in the south-east of France using traps and deliberate field exposures of Ds and D. melanogaster larvae/pupae. Although Ds abundance varied according to sampling methods, it was found to be pervasive and to produce offspring and adults in most conditions (spatial and seasonal). Its main limits are some specific abiotic conditions (i.e., desiccation) as well as interspecific competition. Indeed, Ds mostly co-occurred with D. busckii and D. hydei, probably due to common phenology and/or ecological requirements. These two species thus deserve more attention for risk assessment. The main indigenous parasitoids collected belonged to two pupal species, Trichopria cf drosophilae and Pachycrepoideus vindemmiae, but their presence was observed late in the autumn and mainly in cultivated areas. Results are discussed in a comparison of the methodological approaches for monitoring Drosophilids and the benefits-risks assessment of classical biological control

The cellular immune response of the pea aphid to foreign intrusion and symbiotic challenge

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceRecent studies suggest that the pea aphid (Acyrthosiphon pisum) has low immune defenses. However, its immune components are largely undescribed, and notably, extensive characterization of circulating cells has been missing. Here, we report characterization of five cell categories in hemolymph of adults of the LL01 pea aphid clone, devoid of secondary symbionts (SS): prohemocytes, plasmatocytes, granulocytes, spherulocytes and wax cells. Circulating lipid-filed wax cells are rare; they otherwise localize at the basis of the cornicles. Spherulocytes, that are likely sub-cuticular sessile cells, are involved in the coagulation process. Prohemocytes have features of precursor cells. Plasmatocytes and granulocytes, the only adherent cells, can form a layer in vivo around inserted foreign objects and phagocytize latex beads or Escherichia coli bacteria injected into aphid hemolymph. Using digital image analysis, we estimated that the hemolymph from one LL01 aphid contains about 600 adherent cells, 35% being granulocytes. Among aphid YR2 lines differing only in their SS content, similar results to LL01 were observed for YR2-Amp (without SS) and YR2-Ss (with Serratia symbiotica), while YR2-Hd (with Hamiltonella defensa) and YR2(Ri) (with Regiella insecticola) had strikingly lower adherent hemocyte numbers and granulocyte proportions. The effect of the presence of SS on A. pisum cellular immunity is thus symbiont-dependent. Interestingly, Buchnera aphidicola (the aphid primary symbiont) and all SS, whether naturally present, released during hemolymph collection, or artificially injected, were internalized by adherent hemocytes. Inside hemocytes, SS were observed in phagocytic vesicles, most often in phagolysosomes. Our results thus raise the question whether aphid symbionts in hemolymph are taken up and destroyed by hemocytes, or actively promote their own internalization, for instance as a way of being transmitted to the next generation. Altogether, we demonstrate here a strong interaction between aphid symbionts and immune cells, depending upon the symbiont, highlighting the link between immunity and symbiosis

Closely related parasites targeting the same host can show extensive venom variation: the case of Leptopilina parasitoids of Drosophila

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