74 research outputs found
HAPLN1 potentiates peritoneal metastasis in pancreatic cancer
The presence of peritoneal metastasis in pancreatic cancers is associated with poor prognosis. Here the authors show that hyaluronan and proteoglycan link protein-1 (HAPLN1) promotes tumour cell plasticity and pro-tumoral immune microenvironment to facilitate peritoneal dissemination in pancreatic cancers. Pancreatic ductal adenocarcinoma (PDAC) frequently metastasizes into the peritoneum, which contributes to poor prognosis. Metastatic spreading is promoted by cancer cell plasticity, yet its regulation by the microenvironment is incompletely understood. Here, we show that the presence of hyaluronan and proteoglycan link protein-1 (HAPLN1) in the extracellular matrix enhances tumor cell plasticity and PDAC metastasis. Bioinformatic analysis showed that HAPLN1 expression is enriched in the basal PDAC subtype and associated with worse overall patient survival. In a mouse model for peritoneal carcinomatosis, HAPLN1-induced immunomodulation favors a more permissive microenvironment, which accelerates the peritoneal spread of tumor cells. Mechanistically, HAPLN1, via upregulation of tumor necrosis factor receptor 2 (TNFR2), promotes TNF-mediated upregulation of Hyaluronan (HA) production, facilitating EMT, stemness, invasion and immunomodulation. Extracellular HAPLN1 modifies cancer cells and fibroblasts, rendering them more immunomodulatory. As such, we identify HAPLN1 as a prognostic marker and as a driver for peritoneal metastasis in PDAC
A plant pathogen modulates the effects of secondary metabolites on the performance and immune function of an insect herbivore
Host plant chemical composition critically shapes the performance of insect herbivores feeding on them. Some insects have become specialized on plant secondary metabolites, and even use them to their own advantage such as defense against predators. However, infection by plant pathogens can seriously alter the interaction between herbivores and their host plants. We tested whether the effects of the plant secondary metabolites, iridoid glycosides (IGs), on the performance and immune response of an insect herbivore are modulated by a plant pathogen. We used the IG-specialized Glanville fritillary butterfly Melitaea cinxia, its host plant Plantago lanceolata, and the naturally occurring plant pathogen, powdery mildew Podosphaera plantaginis, as model system. Pre-diapause larvae were fed on P. lanceolata host plants selected to contain either high or low IGs, in the presence or absence of powdery mildew. Larval performance was measured by growth rate, survival until diapause, and by investment in immunity. We assessed immunity after a bacterial challenge in terms of phenoloxidase (PO) activity and the expression of seven pre-selected insect immune genes (qPCR). We found that the beneficial effects of constitutive leaf IGs, that improved larval growth, were significantly reduced by mildew infection. Moreover, mildew presence downregulated one component of larval immune response (PO activity), suggesting a physiological cost of investment in immunity under suboptimal conditions. Yet, feeding on mildew-infected leaves caused an upregulation of two immune genes, lysozyme and prophenoloxidase. Our findings indicate that a plant pathogen can significantly modulate the effects of secondary metabolites on the growth of an insect herbivore. Furthermore, we show that a plant pathogen can induce contrasting effects on insect immune function. We suspect that the activation of the immune system toward a plant pathogen infection may be maladaptive, but the actual infectivity on the larvae should be tested.Peer reviewe
Herbivory on the pedunculate oak along an urbanization gradient in Europe : Effects of impervious surface, local tree cover, and insect feeding guild
Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that-just like in non-urban areas-plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.Peer reviewe
Herbivory on the pedunculate oak along an urbanization gradient in Europe : Effects of impervious surface, local tree cover, and insect feeding guild
Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intraurban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that â just like in non-urban areas â plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.Agence Nationale de la Recherche, Grant/Award Number: ANR-10--LABX-45; Fondation BNP Paribas.info:eu-repo/semantics/publishedVersio
Forest biodiversity, ecosystem functioning and the provision of ecosystem services
Forests are critical habitats for biodiversity and they are also essential for the provision of a wide range of ecosystem services that are important to human well-being. There is increasing evidence that biodiversity contributes to forest ecosystem functioning and the provision of ecosystem services. Here we provide a review of forest ecosystem services including biomass production, habitat provisioning services, pollination, seed dispersal, resistance to wind storms, fire regulation and mitigation, pest regulation of native and invading insects, carbon sequestration, and cultural ecosystem services, in relation to forest type, structure and diversity. We also consider relationships between forest biodiversity and multifunctionality, and trade-offs among ecosystem services. We compare the concepts of ecosystem processes, functions and services to clarify their definitions. Our review of published studies indicates a lack of empirical studies that establish quantitative and causal relationships between forest biodiversity and many important ecosystem services. The literature is highly skewed; studies on provisioning of nutrition and energy, and on cultural services, delivered by mixed-species forests are under-represented. Planted forests offer ample opportunity for optimising their composition and diversity because replanting after harvesting is a recurring process. Planting mixed-species forests should be given more consideration as they are likely to provide a wider range of ecosystem services within the forest and for adjacent land uses. This review also serves as the introduction to this special issue of Biodiversity and Conservation on various aspects of forest biodiversity and ecosystem services
Herbivory on the pedunculate oak along an urbanization gradient in Europe: Effects of impervious surface, local tree cover, and insect feeding guild
Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that-just like in non-urban areas-plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions
Tree biodiversity and forest resistance to biological invasions : application on chestnut and its exotic pest complex, chestnut blight (Cryponectria parasitica) and Asian chestnut gall wasp (Dryocosmus Kuriphilus)
Les plantes sont au centre dâune grande diversitĂ© dâinteractions biotiques entre organismes plus ou moins proches qui les exploitent en tant que ressources. Lâobjectif de cette thĂšse a Ă©tĂ© de comprendre comment les infections fongiques de la plante et la diversitĂ© des arbres en forĂȘt modifient les interactions arbres-insectes. Nous avons tout dâabord effectuĂ© une mĂ©ta-analyse pour poser le cadre thĂ©orique des effets indirects des infections fongiques sur les insectes herbivores associĂ©s aux mĂȘmes plantes hĂŽtes. L'effet de lâinfection prĂ©alable des plantes par les champignons sur les prĂ©fĂ©rences et performances des insectes sâavĂšre gĂ©nĂ©ralement nĂ©gatif. Cependant, la magnitude de cet effet dĂ©lĂ©tĂšre varie selon le mode de vie du champignon, la guilde trophique de lâinsecte et la spatialitĂ© des interactions (interactions locales vs distantes). Nous avons ensuite analysĂ© de façon empirique les interactions tripartites entre le chĂątaignier europĂ©en (Castanea sativa) et deux de ses bioagresseurs exotiques: le cynips (Dryocosmus kuriphilus), insecte galligĂšne, et Cryphonectria parasitica, champignon pathogĂšne responsable de la maladie du chancre. L'effet sur les taux dâinfestation par le cynips de la composition spĂ©cifique en essences forestiĂšres des forĂȘts de chĂątaigniers atteintes de chancre a Ă©tĂ© Ă©galement Ă©tudiĂ©. Afin d'identifier les mĂ©canismes sous-jacents aux effets de la diversitĂ© des forĂȘts sur cet insecte invasif, les communautĂ©s d'insectes parasitoĂŻdes et de champignons endophytes prĂ©sents dans les galles ont Ă©tĂ© dĂ©crites. Les taux dâinfection par le cynips Ă©taient plus faibles dans les mĂ©langes de chĂątaignier avec du chĂȘne et du frĂȘne que dans des parcelles de chĂątaignier monospĂ©cifiques ou dans les mĂ©langes avec du pin. La composition des forĂȘts influence aussi la composition des communautĂ©s de parasitoĂŻdes associĂ©s aux galles du cynips mais pas leur abondance, richesse ou diversitĂ©. Les communautĂ©s de champignons endophytes des galles, Ă©tudiĂ©es par des mĂ©thodes de sĂ©quençage de nouvelle gĂ©nĂ©ration, sont indĂ©pendantes de la composition forestiĂšre. Par contre, celles prĂ©sentes dans les galles diffĂ©rent fortement de celles des tissus foliaires adjacents. Nous avons ainsi apportĂ© de nouvelles preuves que la diversitĂ© des plantes et les champignons pathogĂšnes sont des facteurs clĂ©s dĂ©terminant les interactions plantes-insectes. Etudier comment les plantes interagissent avec leurs insectes et champignons associĂ©s, et les mĂ©canismes sous-jacents Ă lâeffet de la diversitĂ© des plantes sur ces interactions, doit permettre de mieux comprendre les relations entre diversitĂ© et fonctionnement des Ă©cosystĂšmes et de proposer des applications pour la gestion des bio-agresseurs forestiers natifs et exotiques.Plants are the playground of a large diversity of biotic interactions between related and unrelated organisms exploiting them as common resources. The aim of this thesis was to understand how plant-insect interactions vary with fungal infection of their host plant and plant diversity. I first performed a meta-analysis to provide a theoretical background for plant-mediated effects of fungal infection on herbivorous insects. Overall, I found a negative plant-mediated effect of fungi on both insect preference and performance. However, this effect varied according to fungus lifestyle, insect feeding guild and spatial location of the interactions (local vs distant). Then I experimentally tested plant-fungus-insect tripartite interactions in the particular case of exotic bio-aggressors of the European chestnut (Castanea sativa): the Asian chestnut Gall Wasp (ACGW, Dryocosmus kuriphilus), and the fungal pathogen Cryphonectria parasitica, the causal agent of chestnut blight. I performed an observational study, in natural chestnut forest stands in Italy, where I tested how ACGW infestation rates vary with the tree species composition. I also investigated the mechanisms underlying plant diversity effects on the invasive pest, with a particular focus on its natural enemies such as insect parasitoids and endophytic fungi. ACGW infestation rates was lower in oak and ash chestnut mixtures compared to monocultures or pine-chestnut mixtures. Plot composition also influenced ACGW parasitoid community composition but not their abundances, diversity or richness. Endophytic communities of galls, described by using next generation sequencing methods, did not vary with plot composition. However, they strongly differed from surrounding leaf tissues. We thus provided evidence that plant diversity and fungal pathogens are key drivers of plant-insect interactions. Understanding how plants interact with associated insects and fungi, and mechanisms underlying plant diversity effect on these interactions, will improve our knowledge on diversity-ecosystem functioning relationships and will have practical applications for the management of native and exotic forest pests
Tree biodiversity and forest resistance to biological invasions : application on chestnut and its exotic pest complex, chestnut blight (Cryponectria parasitica) and Asian chestnut gall wasp (Dryocosmus Kuriphilus)
Les plantes sont au centre dâune grande diversitĂ© dâinteractions biotiques entre organismes plus ou moins proches qui les exploitent en tant que ressources. Lâobjectif de cette thĂšse a Ă©tĂ© de comprendre comment les infections fongiques de la plante et la diversitĂ© des arbres en forĂȘt modifient les interactions arbres-insectes. Nous avons tout dâabord effectuĂ© une mĂ©ta-analyse pour poser le cadre thĂ©orique des effets indirects des infections fongiques sur les insectes herbivores associĂ©s aux mĂȘmes plantes hĂŽtes. L'effet de lâinfection prĂ©alable des plantes par les champignons sur les prĂ©fĂ©rences et performances des insectes sâavĂšre gĂ©nĂ©ralement nĂ©gatif. Cependant, la magnitude de cet effet dĂ©lĂ©tĂšre varie selon le mode de vie du champignon, la guilde trophique de lâinsecte et la spatialitĂ© des interactions (interactions locales vs distantes). Nous avons ensuite analysĂ© de façon empirique les interactions tripartites entre le chĂątaignier europĂ©en (Castanea sativa) et deux de ses bioagresseurs exotiques: le cynips (Dryocosmus kuriphilus), insecte galligĂšne, et Cryphonectria parasitica, champignon pathogĂšne responsable de la maladie du chancre. L'effet sur les taux dâinfestation par le cynips de la composition spĂ©cifique en essences forestiĂšres des forĂȘts de chĂątaigniers atteintes de chancre a Ă©tĂ© Ă©galement Ă©tudiĂ©. Afin d'identifier les mĂ©canismes sous-jacents aux effets de la diversitĂ© des forĂȘts sur cet insecte invasif, les communautĂ©s d'insectes parasitoĂŻdes et de champignons endophytes prĂ©sents dans les galles ont Ă©tĂ© dĂ©crites. Les taux dâinfection par le cynips Ă©taient plus faibles dans les mĂ©langes de chĂątaignier avec du chĂȘne et du frĂȘne que dans des parcelles de chĂątaignier monospĂ©cifiques ou dans les mĂ©langes avec du pin. La composition des forĂȘts influence aussi la composition des communautĂ©s de parasitoĂŻdes associĂ©s aux galles du cynips mais pas leur abondance, richesse ou diversitĂ©. Les communautĂ©s de champignons endophytes des galles, Ă©tudiĂ©es par des mĂ©thodes de sĂ©quençage de nouvelle gĂ©nĂ©ration, sont indĂ©pendantes de la composition forestiĂšre. Par contre, celles prĂ©sentes dans les galles diffĂ©rent fortement de celles des tissus foliaires adjacents. Nous avons ainsi apportĂ© de nouvelles preuves que la diversitĂ© des plantes et les champignons pathogĂšnes sont des facteurs clĂ©s dĂ©terminant les interactions plantes-insectes. Etudier comment les plantes interagissent avec leurs insectes et champignons associĂ©s, et les mĂ©canismes sous-jacents Ă lâeffet de la diversitĂ© des plantes sur ces interactions, doit permettre de mieux comprendre les relations entre diversitĂ© et fonctionnement des Ă©cosystĂšmes et de proposer des applications pour la gestion des bio-agresseurs forestiers natifs et exotiques.Plants are the playground of a large diversity of biotic interactions between related and unrelated organisms exploiting them as common resources. The aim of this thesis was to understand how plant-insect interactions vary with fungal infection of their host plant and plant diversity. I first performed a meta-analysis to provide a theoretical background for plant-mediated effects of fungal infection on herbivorous insects. Overall, I found a negative plant-mediated effect of fungi on both insect preference and performance. However, this effect varied according to fungus lifestyle, insect feeding guild and spatial location of the interactions (local vs distant). Then I experimentally tested plant-fungus-insect tripartite interactions in the particular case of exotic bio-aggressors of the European chestnut (Castanea sativa): the Asian chestnut Gall Wasp (ACGW, Dryocosmus kuriphilus), and the fungal pathogen Cryphonectria parasitica, the causal agent of chestnut blight. I performed an observational study, in natural chestnut forest stands in Italy, where I tested how ACGW infestation rates vary with the tree species composition. I also investigated the mechanisms underlying plant diversity effects on the invasive pest, with a particular focus on its natural enemies such as insect parasitoids and endophytic fungi. ACGW infestation rates was lower in oak and ash chestnut mixtures compared to monocultures or pine-chestnut mixtures. Plot composition also influenced ACGW parasitoid community composition but not their abundances, diversity or richness. Endophytic communities of galls, described by using next generation sequencing methods, did not vary with plot composition. However, they strongly differed from surrounding leaf tissues. We thus provided evidence that plant diversity and fungal pathogens are key drivers of plant-insect interactions. Understanding how plants interact with associated insects and fungi, and mechanisms underlying plant diversity effect on these interactions, will improve our knowledge on diversity-ecosystem functioning relationships and will have practical applications for the management of native and exotic forest pests
DiversitĂ© des arbres et rĂ©sistance des forĂȘts aux invasions biologiques : application au chataignier et son complexe de bioagresseurs exotiques, chancre (Cryphonectria parasitica) et cynips (Dryocosmus Kuriphilus)
Plants are the playground of a large diversity of biotic interactions between related and unrelated organisms exploiting them as common resources. The aim of this thesis was to understand how plant-insect interactions vary with fungal infection of their host plant and plant diversity. I first performed a meta-analysis to provide a theoretical background for plant-mediated effects of fungal infection on herbivorous insects. Overall, I found a negative plant-mediated effect of fungi on both insect preference and performance. However, this effect varied according to fungus lifestyle, insect feeding guild and spatial location of the interactions (local vs distant). Then I experimentally tested plant-fungus-insect tripartite interactions in the particular case of exotic bio-aggressors of the European chestnut (Castanea sativa): the Asian chestnut Gall Wasp (ACGW, Dryocosmus kuriphilus), and the fungal pathogen Cryphonectria parasitica, the causal agent of chestnut blight. I performed an observational study, in natural chestnut forest stands in Italy, where I tested how ACGW infestation rates vary with the tree species composition. I also investigated the mechanisms underlying plant diversity effects on the invasive pest, with a particular focus on its natural enemies such as insect parasitoids and endophytic fungi. ACGW infestation rates was lower in oak and ash chestnut mixtures compared to monocultures or pine-chestnut mixtures. Plot composition also influenced ACGW parasitoid community composition but not their abundances, diversity or richness. Endophytic communities of galls, described by using next generation sequencing methods, did not vary with plot composition. However, they strongly differed from surrounding leaf tissues. We thus provided evidence that plant diversity and fungal pathogens are key drivers of plant-insect interactions. Understanding how plants interact with associated insects and fungi, and mechanisms underlying plant diversity effect on these interactions, will improve our knowledge on diversity-ecosystem functioning relationships and will have practical applications for the management of native and exotic forest pests.Les plantes sont au centre dâune grande diversitĂ© dâinteractions biotiques entre organismes plus ou moins proches qui les exploitent en tant que ressources. Lâobjectif de cette thĂšse a Ă©tĂ© de comprendre comment les infections fongiques de la plante et la diversitĂ© des arbres en forĂȘt modifient les interactions arbres-insectes. Nous avons tout dâabord effectuĂ© une mĂ©ta-analyse pour poser le cadre thĂ©orique des effets indirects des infections fongiques sur les insectes herbivores associĂ©s aux mĂȘmes plantes hĂŽtes. L'effet de lâinfection prĂ©alable des plantes par les champignons sur les prĂ©fĂ©rences et performances des insectes sâavĂšre gĂ©nĂ©ralement nĂ©gatif. Cependant, la magnitude de cet effet dĂ©lĂ©tĂšre varie selon le mode de vie du champignon, la guilde trophique de lâinsecte et la spatialitĂ© des interactions (interactions locales vs distantes). Nous avons ensuite analysĂ© de façon empirique les interactions tripartites entre le chĂątaignier europĂ©en (Castanea sativa) et deux de ses bioagresseurs exotiques: le cynips (Dryocosmus kuriphilus), insecte galligĂšne, et Cryphonectria parasitica, champignon pathogĂšne responsable de la maladie du chancre. L'effet sur les taux dâinfestation par le cynips de la composition spĂ©cifique en essences forestiĂšres des forĂȘts de chĂątaigniers atteintes de chancre a Ă©tĂ© Ă©galement Ă©tudiĂ©. Afin d'identifier les mĂ©canismes sous-jacents aux effets de la diversitĂ© des forĂȘts sur cet insecte invasif, les communautĂ©s d'insectes parasitoĂŻdes et de champignons endophytes prĂ©sents dans les galles ont Ă©tĂ© dĂ©crites. Les taux dâinfection par le cynips Ă©taient plus faibles dans les mĂ©langes de chĂątaignier avec du chĂȘne et du frĂȘne que dans des parcelles de chĂątaignier monospĂ©cifiques ou dans les mĂ©langes avec du pin. La composition des forĂȘts influence aussi la composition des communautĂ©s de parasitoĂŻdes associĂ©s aux galles du cynips mais pas leur abondance, richesse ou diversitĂ©. Les communautĂ©s de champignons endophytes des galles, Ă©tudiĂ©es par des mĂ©thodes de sĂ©quençage de nouvelle gĂ©nĂ©ration, sont indĂ©pendantes de la composition forestiĂšre. Par contre, celles prĂ©sentes dans les galles diffĂ©rent fortement de celles des tissus foliaires adjacents. Nous avons ainsi apportĂ© de nouvelles preuves que la diversitĂ© des plantes et les champignons pathogĂšnes sont des facteurs clĂ©s dĂ©terminant les interactions plantes-insectes. Etudier comment les plantes interagissent avec leurs insectes et champignons associĂ©s, et les mĂ©canismes sous-jacents Ă lâeffet de la diversitĂ© des plantes sur ces interactions, doit permettre de mieux comprendre les relations entre diversitĂ© et fonctionnement des Ă©cosystĂšmes et de proposer des applications pour la gestion des bio-agresseurs forestiers natifs et exotiques
Tree biodiversity and forest resistance to biological invasions : application on chestnut and its exotic pest complex, chestnut blight (Cryponectria parasitica) and Asian chestnut gall wasp (Dryocosmus Kuriphilus)
Les plantes sont au centre dâune grande diversitĂ© dâinteractions biotiques entre organismes plus ou moins proches qui les exploitent en tant que ressources. Lâobjectif de cette thĂšse a Ă©tĂ© de comprendre comment les infections fongiques de la plante et la diversitĂ© des arbres en forĂȘt modifient les interactions arbres-insectes. Nous avons tout dâabord effectuĂ© une mĂ©ta-analyse pour poser le cadre thĂ©orique des effets indirects des infections fongiques sur les insectes herbivores associĂ©s aux mĂȘmes plantes hĂŽtes. L'effet de lâinfection prĂ©alable des plantes par les champignons sur les prĂ©fĂ©rences et performances des insectes sâavĂšre gĂ©nĂ©ralement nĂ©gatif. Cependant, la magnitude de cet effet dĂ©lĂ©tĂšre varie selon le mode de vie du champignon, la guilde trophique de lâinsecte et la spatialitĂ© des interactions (interactions locales vs distantes). Nous avons ensuite analysĂ© de façon empirique les interactions tripartites entre le chĂątaignier europĂ©en (Castanea sativa) et deux de ses bioagresseurs exotiques: le cynips (Dryocosmus kuriphilus), insecte galligĂšne, et Cryphonectria parasitica, champignon pathogĂšne responsable de la maladie du chancre. L'effet sur les taux dâinfestation par le cynips de la composition spĂ©cifique en essences forestiĂšres des forĂȘts de chĂątaigniers atteintes de chancre a Ă©tĂ© Ă©galement Ă©tudiĂ©. Afin d'identifier les mĂ©canismes sous-jacents aux effets de la diversitĂ© des forĂȘts sur cet insecte invasif, les communautĂ©s d'insectes parasitoĂŻdes et de champignons endophytes prĂ©sents dans les galles ont Ă©tĂ© dĂ©crites. Les taux dâinfection par le cynips Ă©taient plus faibles dans les mĂ©langes de chĂątaignier avec du chĂȘne et du frĂȘne que dans des parcelles de chĂątaignier monospĂ©cifiques ou dans les mĂ©langes avec du pin. La composition des forĂȘts influence aussi la composition des communautĂ©s de parasitoĂŻdes associĂ©s aux galles du cynips mais pas leur abondance, richesse ou diversitĂ©. Les communautĂ©s de champignons endophytes des galles, Ă©tudiĂ©es par des mĂ©thodes de sĂ©quençage de nouvelle gĂ©nĂ©ration, sont indĂ©pendantes de la composition forestiĂšre. Par contre, celles prĂ©sentes dans les galles diffĂ©rent fortement de celles des tissus foliaires adjacents. Nous avons ainsi apportĂ© de nouvelles preuves que la diversitĂ© des plantes et les champignons pathogĂšnes sont des facteurs clĂ©s dĂ©terminant les interactions plantes-insectes. Etudier comment les plantes interagissent avec leurs insectes et champignons associĂ©s, et les mĂ©canismes sous-jacents Ă lâeffet de la diversitĂ© des plantes sur ces interactions, doit permettre de mieux comprendre les relations entre diversitĂ© et fonctionnement des Ă©cosystĂšmes et de proposer des applications pour la gestion des bio-agresseurs forestiers natifs et exotiques.Plants are the playground of a large diversity of biotic interactions between related and unrelated organisms exploiting them as common resources. The aim of this thesis was to understand how plant-insect interactions vary with fungal infection of their host plant and plant diversity. I first performed a meta-analysis to provide a theoretical background for plant-mediated effects of fungal infection on herbivorous insects. Overall, I found a negative plant-mediated effect of fungi on both insect preference and performance. However, this effect varied according to fungus lifestyle, insect feeding guild and spatial location of the interactions (local vs distant). Then I experimentally tested plant-fungus-insect tripartite interactions in the particular case of exotic bio-aggressors of the European chestnut (Castanea sativa): the Asian chestnut Gall Wasp (ACGW, Dryocosmus kuriphilus), and the fungal pathogen Cryphonectria parasitica, the causal agent of chestnut blight. I performed an observational study, in natural chestnut forest stands in Italy, where I tested how ACGW infestation rates vary with the tree species composition. I also investigated the mechanisms underlying plant diversity effects on the invasive pest, with a particular focus on its natural enemies such as insect parasitoids and endophytic fungi. ACGW infestation rates was lower in oak and ash chestnut mixtures compared to monocultures or pine-chestnut mixtures. Plot composition also influenced ACGW parasitoid community composition but not their abundances, diversity or richness. Endophytic communities of galls, described by using next generation sequencing methods, did not vary with plot composition. However, they strongly differed from surrounding leaf tissues. We thus provided evidence that plant diversity and fungal pathogens are key drivers of plant-insect interactions. Understanding how plants interact with associated insects and fungi, and mechanisms underlying plant diversity effect on these interactions, will improve our knowledge on diversity-ecosystem functioning relationships and will have practical applications for the management of native and exotic forest pests
- âŠ