Differences in Volatile Profiles of Turnip Plants Subjected to Single and Dual Herbivory Above- and Belowground

Plants attacked by herbivorous insects emit volatile organic compounds that are used by natural enemies to locate their host or prey. The composition of the blend is often complex and specific. It may vary qualitatively and quantitatively according to plant and herbivore species, thus providing specific information for carnivorous arthropods. Most studies have focused on simple interactions that involve one species per trophic level, and typically have investigated the aboveground parts of plants. These investigations need to be extended to more complex networks that involve multiple herbivory above- and belowground. A previous study examined whether the presence of the leaf herbivore Pieris brassicae on turnip plants (Brassica rapa subsp. rapa) influences the response of Trybliographa rapae, a specialist parasitoid of the root feeder Delia radicum. It showed that the parasitoid was not attracted by volatiles emitted by plants under simultaneous attack. Here, we analyzed differences in the herbivore induced plant volatile (HIPV) mixtures that emanate from such infested plants by using Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA). This multivariate model focuses on the differences between odor blends, and highlights the relative importance of each compound in an HIPV blend. Dual infestation resulted in several HIPVs that were present in both isolated infestation types. However, HIPVs collected from simultaneously infested plants were not the simple combination of volatiles from isolated forms of above- and belowground herbivory. Only a few specific compounds characterized the odor blend of each type of damaged plant. Indeed, some compounds were specifically induced by root herbivory (4-methyltridecane and salicylaldehyde) or shoot herbivory (methylsalicylate), whereas hexylacetate, a green leaf volatile, was specifically induced after dual herbivory. It remains to be determined whether or not these minor quantitative variations, within the background of more commonly induced odors, are involved in the reduced attraction of the root feeder’s parasitoid. The mechanisms involved in the specific modification of the odor blends emitted by dual infested turnip plants are discussed in the light of interferences between biosynthetic pathways linked to plant responses to shoot or root herbivory

Les composés secondaires soufres des Allium (rôle dans les systèmes de défense du poireau et actions sur la biologie des insectes)

Allium plant species such the leek, Allium porrum, produce sulphur secondary compounds. These compounds seem to be involved in Allium plants defence processes. Toxicity tests realised in confined atmosphere showed that sulphur compounds, thiosulfinates and disulfides, emitted by the leek, are very toxic against the different tested species. One of these compounds, dimethyl disulfide (DMDS), kill insects by an inhibition of the mitochondrial respiratory chain complex IV (cytochrome oxydase). This DMDS-induced inhibition of complex IV subsequently decreased the intracellular ATP concentration, which thereby activated KATP channels mediating membrane hyperpolarisation and reduction of neuronal activity. Nevertheless, the larvae of leek moth, Acrolepiopsis assectella, specialist lepidoptera of Allium plant species were less susceptible to these sulphr compounds than the other tested species. This insect has developed unknowed specific mecanism to better tolerate sulphur compounds. By repulsive and toxicity phenomena, sulphur compounds produced by Allium plants act in the field as constitutive direct defence against non specialist insects of Allium plants. This defence process could certainely explain why there is only a few number of insect species being able to consume leek leaves. When they are strongly attack by leek moth, leek plants respond by an increase of non volatile sulphur compounds production which can leads to an increase of sulphur volatiles emission. This induced response has consequences on leek moth subsequent performances and thereby could be considered as an induced direct defence. Besides, the sulphur volatile compounds emitted by induced leeks are attractives for the leek moth natural enemy, the parasitic wasp, Diadromus pulchellus. In this way sulphur compounds produced by leek plants could be involved both in direct and indirect defence against the leek moth.Les végétaux appartenant au genre Allium et notamment le poireau, Allium porrum, ont la caractéristique de produire des composés secondaires soufrés. A l instar de nombreuses substances issues du métabolisme secondaire des plantes, ces composés soufrés semblent être impliqués dans les systèmes de défense naturelle des Allium. Les tests de toxicité réalisés sur différentes espèces d insectes ont révélé que les substances volatiles soufrées émises par ces plantes, les thiosulfinates et leurs produits de dégradation, les disulfures et notamment le disulfure de diméthyle (DMDS) sont toxiques vis à vis de toutes les espèces testées. Le DMDS provoque la mort des insectes par un disfonctionnement mitochondrial via l inhibition de la cytochrome oxydase conduisant à une forte diminution de la production d ATP et de ce fait, à une perte de l influx nerveux. Toutefois, les larves de la teigne du poireau, Acrolepiopsis assectella, lépidoptère spécialiste des Allium et notamment du poireau, sont nettement moins sensibles à ces substances soufrées que les autres espèces. Cet insecte a développé des mécanismes adaptatifs spécifiques mais pour l instant inconnus lui conférant cette meilleure tolérance et donc la possibilité de se développer sur sa plante hôte riche en substances soufrées. Les composés secondaires soufrés produits de façon constitutive par les poireaux agissent très certainement dans la nature par des phénomènes d anti-appétence, de répulsion et de toxicité et représentent alors un système de défense constitutive directe vis à vis des insectes non inféodés à ces plantes. Ce système de défense peut probablement expliquer pourquoi si peu d espèces phytophages sont capables de se développer aux dépens du poireau. Lorsqu il est attaqué de façon importante par la teigne du poireau, le poireau met en place une réponse se traduisant par une augmentation de la production de composés soufrés non volatils pouvant aboutir à une émission plus importante de substances soufrées volatiles. Cette réponse du poireau induite par l attaque des teignes a des répercussions sur le comportement et les capacités de développement du lépidoptère spécialiste et semble ainsi représenter pour la plante un système de défense directe induite. Les composés soufrés volatils émis par le poireau en ayant un rôle très important dans le comportement de recherche de l hôte par Diadromus pulchellus, parasitoïde spécialiste des chrysalides de teignes du poireau pourraient être également impliqués dans un phénomène de défense indirecte de la plante.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

First steps to the development of a « Push-Pull » strategy to protect broccoli plants against the cabbage root fly

International audienc

Using HIPV’s to manipulate multitrophic interactions and improve crop protection

International audienc

Toward « Push-Pull » strategy to protect Brassiaceae against cabbage root fly

International audienc

Réponses induites des Brassicacées vis-à-vis de la mouche du chou (Delia radicum L.) et interactions avec d autres insectes associés

Les plantes sont capables de mettre en place des systèmes de défenses en réponse à l attaque des insectes phytophages. Les études décrivant ces phénomènes se sont essentiellement focalisées sur des interactions simplifiées impliquant le compartiment foliaire d une plante, un insecte phytophage et un ennemi naturel. Ce travail de thèse s intéresse aux réponses induites des Brassicacées vis-à-vis de la Mouche du chou Delia radicum dans un contexte multitrophique. Nous avons démontré que la présence du phytophage foliaire Pieris brassicae altère les défenses indirectes du navet et du brocoli vis-à-vis de la Mouche du chou. Des études d olfactométrie couplées à des analyses chimiques montrent en effet que la présence additionnelle du phytophage foliaire non-hôte induit des variations quantitatives spécifiques dans le bouquet d odeurs émis par la plante, à l origine d une perturbation de l orientation de Trybliographa rapae, parasitoïde de D. radicum. En outre, l application d acide jasmonique et une pré-infestation par D. radicum des racines de navet et de brocoli modifient la chimie de la plante et la performance larvaire de D. radicum en condition contrôlée. En plein champ les réponses induites par ces traitements affectent la colonisation des plantes par des populations naturelles de D. radicum et la structuration de la communauté des insectes phytophages foliaires associées à la même plante hôte. Cette étude a permis de démontrer que les réponses induites des végétaux sont à la base d interactions complexes entre des insectes associés à des compartiments différents d une même plante hôte.Plants have evolved various defense strategies in response to attack by phytophagous insects. Related studies have essentially focused on simple interactions involving the aboveground plant compartment, a single herbivore species and its natural ennemy. The present study investigates Brassicaceous plant induced responses to the Cabbage root fly Delia radicum in a multitrophic context. It was shown that the presence of the leaf herbivore Pieris brassicae alters the indirect defenses of turnip and broccoli plants against the cabbage root fly. Indeed, olfactometer tests coupled with chemical analysis revealed that the additionnal presence of the non-host leaf herbivore induces some specific quantitative variations in the volatile blend emitted by the plant, which could result in the reduced attractiveness towards Trybliographa rapae, a parasitoid of the cabbage root fly. Furthermore, jasmonic acid root application and previous infestation by D. radicum were found to modify plant chemistry and larval performance of D. radicum under controlled conditions. In the field, such induced responses to root treatments affect not only plant colonization by natural populations of D. radicum but also the structuration of phytophagous insect communities associated to the same host plant. In conclusion, this study highlights plant induced responses as key players of complex interactions between insect herbivores associated to above- and belowground compartments of the same host plant.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Correlations of cibarial muscle activities of Homalodisca spp. sharpshooters (Hemiptera: Cicadellidae) with EPG ingestion waveform and excretion

International audienceFluid flow into and out of the stylets of xylem-ingesting sharpshooters (Hemiptera: Cicadellidae: Cicadellinae) is powered by muscles of the cibarial pump. Such fluid flow is crucial for transmission of Xylella fastidiosa, the Pierce’s Disease bacterium, yet has not been rigorously studied via electrical penetration graph (EPG) technology. We correlated EPG waveforms with electromyographically (EMG) recorded muscle potentials from the cibarial dilator muscles, which power the piston-like cibarial diaphragm. There was a 1:1 correspondence of each cycle of cibarial muscle contraction/relaxation with each plateau of EPG waveform C. Results definitively showed that the C waveform represents active ingestion, i.e. fluid flow is propelled by cibarial muscle contraction. Moreover, each C waveform episode represents muscular diaphragm uplift, probably combined with a “bounce” from cuticular elasticity, to provide the suction that pulls fluid into the stylets. Fine structure of the EPG ingestion waveform represents directionality of fluid flow, supporting the primary role of streaming potentials as the electrical origin of the C waveform. Rhythmic bouts of cibarial pumping were generally correlated with sustained production of excretory droplets. However, neither the onset nor cessation of ingestion was correlated with onset or cessation of excretion, respectively. Volume of excreta is an inexact measure of ingestion. Implications for using EPG to understand the mechanism of X. fastidiosa transmission are discusse

Root feeders induce volatiles attracting predators

International audienc

Islet Creation Increases Nesting Opportunities of the Pied Avocet (Recurvirostra avosetta) in a Managed Salt Pan Area

International audienceThe effectiveness of islet creation and restoration on Pied Avocet (Recurvirostra avosetta) nesting was assessed in 14 ponds (six managed islets of 140 m(2) on average per managed pond) from a salt pan complex located on the coast of the Loire-Atlantique department in northwest France. A Before-After-Control-Impact design using the two years before and the two years following management was used. No nesting occurred in the control ponds that lacked suitable islets. In the managed ponds, the mean number of nests built per year in the two years following management was seven, whereas no nesting occurred in the two years before management (P = 0.002). On the basis of the number of nests built in the study site, the mean proportion of nests built each year in the managed ponds was 27%. The mean age of banded birds nesting for the first time in the managed ponds in the two years following management was 4 years, and 58% of these birds were born in the study site. These results support the hypothesis that such management actions can increase nesting opportunities in artificial habitats. These actions may provide important alternatives to birds when conditions change in previously suitable breeding grounds

Défenses induites

National audienceCet ouvrage présente les grandes fonctions des insectes, leur fonctionnement individuel et collectif, leurs interactions plus ou moins intimes avec les composantes de l’écosystème, en particulier les plantes, en s’appuyant sur l’histoire évolutive à l’origine de ces interactions. Il décrit les multiples applications des recherches sur les insectes pour l’agricultur