Voici les éléments 1 - 3 sur 3
  • Publication
    Métadonnées seulement
    The importance of root-produced volatiles as foraging cues for entomopathogenic nematodes (Marschner Review for the "Rhizosphere 3" Special Issue)
    Background Entomopathogenic nematodes (EPNs) are tiny parasitic worms that parasitize insects, in which they reproduce. Their foraging behavior has been subject to numerous studies, most of which have proposed that, at short distances, EPNs use chemicals that are emitted directly from the host as host location cues. Carbon dioxide (CO2) in particular has been implicated as an important cue. Recent evidence shows that at longer distances several EPNs take advantage of volatiles that are specifically emitted by roots in response to insect attack. Studies that have revealed these plant-mediated interactions among three trophic levels have been met with some disbelief. Scope This review aims to take away this skepticism by summarizing the evidence for a role of root volatiles as foraging cues for EPNs. To reinforce our argument, we conducted olfactometer assays in which we directly compared the attraction of an EPN species to CO2 and two typical inducible root volatiles. Conclusions The combination of the ubiquitous gas and a more specific root volatile was found to be considerably more attractive than one of the two alone. Hence, future studies on EPN foraging behavior should take into account that CO2 and plant volatiles may work in synergy as attractants for EPNs. Recent research efforts also reveal prospects of exploiting plant-produced signals to improve the biological control of insect pests in the rhizosphere.
  • Publication
    Accès libre
    Simultaneous feeding by aboveground and belowground herbivores attenuates plant-mediated attraction of their respective natural enemies
    Herbivore-damaged plants emit volatile organic compounds that attract natural enemies of the herbivores. This form of indirect plant defence occurs aboveground as well as belowground, but it remains unclear how simultaneous feeding by different herbivores attacking leaves and roots may affect the production of the respective defence signals. We employed a setup that combines trapping of volatile organic signals and simultaneous measurements of the attractiveness of these signals to above and belowground natural enemies. Young maize plants were infested with either the foliar herbivore Spodoptera littoralis, the root herbivore Diabrotica virgifera virgifera, or with both these important pest insects. The parasitic wasp Cotesia marginiventris and the entomopathogenic nematode Heterorhabditis megidis were strongly attracted if their respective host was feeding on a plant, but this attraction was significantly reduced if both herbivores were on a plant. The emission of the principal root attractant was indeed reduced due to double infestation, but this was not evident for the leaf volatiles. The parasitoid showed an ability to learn the differences in odour emissions and increased its response to the odour of a doubly infested plant after experiencing this odour during an encounter with hosts. This first study to measure effects of belowground herbivory on aboveground tritrophic signalling and vice-versa reemphasizes the important role of plants in bridging interactions between spatially distinct components of the ecosystem.
  • Publication
    Accès libre
    Belowground tritrophic interactions
    (2006) ;
    Turlings, T.
    En réponse à des dommages causés par les insectes phytophages, les plantes produisent des composés volatiles signalant aux ennemis naturels de l’herbivore la présence d’hôtes ou de proies. D’importants progrès ont été réalisés dans la compréhension de telles interactions trophiques se déroulant aux alentours de la partie aérienne de la plante. De nos jours, l’influence des communautés souterraines, par l’intermédiaire de changements physiologiques et biochimiques de la plante, sur les communautés aériennes est de plus en plus reconnue. Le contenu de cette thèse vise à apporter de nouveaux points de vue sur ces interactions. Le modèle étudié était composé de plantes de maïs (Zea mais L.) dont les feuilles étaient soumises aux attaques du ver du cotonnier (Spodoptera littoralis Boisduval) et les racines aux attaques de la chrysomèle du maïs (Diabrotica virgifera virgifera LeConte). Le développement d’un olfactomètre souterrain à 6 bras nous a permis de mener une étude sur les interactions tritrophiques se déroulant dans le sol. Grâce à l’utilisation de ce dispositif, nous avons découvert que les racines d’une plante attaquée par Diabrotica émettent une substance attirant les nématodes entomopathogènes Heterorhabditis megidis Poinar, Jakson & Klein. Cette attirance est principalement le résultat de l’émission dans le sol, par les racines dévorées, d’un sesquiterpène, le (E)--caryophyllene. L’importance de ce dernier lors du phénomène d’attirance des nématodes fût également confirmée au travers d’expériences en champ lors desquelles nous avons comparé des variétés de maïs productrices de (E)--caryophyllene avec des variétés ayant perdu cette faculté (Chapitre I). Afin d’analyser l’effet croisé entre les interactions aériennes et souterraines et le rôle de la plante en tant que vecteur dudit effet, nous avons connectés l’olfactomètre souterrain à un olfactomètre aérien. Grâce ce nouvel assemblage, nous avons étudié simultanément l’attirance de guêpes parasites et de nématodes en fonction des odeurs émises par les plantes de maïs attaquées par des herbivores soit dans leur partie aérienne, soit souterraine ou encore lors d’une attaque simultanée des deux parties. Il a été démontré que les ravages du système racinaire influencent les interactions tritrophiques aériennes de même que les ravages du système foliaire ont pour résultat la modification des interactions tritrophiques souterraines (Chapitre II). La spécificité de cette nouvelle interaction trophique souterraine fût testée en utilisant différentes espèces de plantes, d’insectes herbivores et de nématodes (Chapitre III). En parallèle à l’intérêt fondamental concernant l’écologie et les mécanismes régulant ces interactions multitrophiques, cette recherche fût également conduite dans l’optique d’améliorer les possibilités de lutte biologique contre les deux importants ravageurs étudiés. D’un point de vue plus général, cette thèse contribue à la compréhension du rôle joué par l’émission de volatiles induits lors d’interactions tritrophiques, qu’elle soit souterraine ou aérienne. Elle met également en lumière l’influence réciproque des interactions se déroulant dans ces deux milieux. De plus, cette thèse démontre pour la première fois, à notre connaissance, que les stratégies de défense indirecte des plantes peuvent améliorer, dans des conditions réelles, l’efficacité d’agents utilisés pour la lutte biologique, In response to phytophagous insects attack, plants produce volatile compounds that can serve as cues for natural enemies of the herbivore to locate their host or prey. Very substantial progress has been made in understanding such tritrophic interactions aboveground. Recently, however, it is more and more recognized that aboveground communities are influenced through physiological and biochemical changes in plants driven by belowground communities and the current thesis aimed to provide new insight in these interactions. Corn (Zea mais L.) plants attacked by the leaf feeder noctuid butterfly (Spodoptera littoralis Boisduval) and the root feeder larvae of the western corn rootworm (Diabrotica virgifera virgifera) were used as a model system. We investigated belowground tritrophic interactions by developing a belowground six arm olfactometer. With the use of this device we discovered that Diabrotica-attacked plants emit an attractant for the entomopathogenic nematode Heterorhabditis megidis Poinar, Jackson & Klein. The attraction was mainly caused by the release of the sesquiterpene (E)--caryophyllene in the soil after root feeding. The importance of the compound in the attraction for the nematodes was further confirmed in field experiments using (E)--caryophyllene producing and non-producing corn varieties (Chapter I). To investigate cross effects between plant-mediated below- and aboveground interactions we connected an above- and a belowground olfactometer, and used this assembly to simultaneously study attraction of parasitic wasps and nematode to the odour emissions of maize after herbivory by either the above or the below ground herbivore, or by both. It was found that indeed root feeding influences aboveground tritrophic interactions, and vice-versa leaf feeding influences belowground tritrophic interactions (Chapter II). The specificity of the newly discovered belowground interaction was tested by using different plant, herbivore and nematode species (Chapter III). Besides a fundamental interest in the ecology and mechanisms involved multitrophic interactions, the work was also driven by an interest to find ways of enhancing a possible biological control of the two major maize pests that were under study. Overall the thesis contributed to our understanding of the role of induced plant volatiles in above- and belowground tritrophic interactions and of how these two interactions may influence one another. Moreover, the thesis is, to our knowledge, the first to demonstrate in the field that indirect plant defences can indeed be used to enhance the efficacy of a biological control agent