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Turlings, Ted
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Turlings, Ted
Affiliation principale
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Professeur.e ordinaire
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ted.turlings@unine.ch
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Voici les éléments 1 - 9 sur 9
- PublicationAccès libreField evidence for the role of plant volatiles induced by caterpillar-derived elicitors in the prey location behavior of predatory social wasps1. One assumed function of herbivore-induced plant volatiles (HIPVs) is to attract natural enemies of the inducing herbivores. Field evidence for this is scarce and often indirect. Also, the assumption that elicitors in insect oral secretions that trigger the volatile emissions are essential for attraction of natural enemies has not yet been demonstrated under field conditions. 2. After observing social wasps removing caterpillars from maize plants in an agricultural field, we hypothesized that these wasps use HIPVs to locate their prey. To test this, we conducted an experiment that simultaneously explored the importance of caterpillar oral secretions in the interaction. 3. We found that Spodoptera caterpillars placed on mechanically damaged plants treated with oral secretion were more likely to be attacked by wasps compared to caterpillars on plants that were only mechanically wounded. Both of the the latter treatments were considerably more attractive than plants that were only treated with oral secretion or left untreated. Subsequent analyses of headspace volatiles confirmed differences in emitted volatiles that likely account for the differential predation events across the treatments. 4. These findings highlight the importance of HIPVs in prey location by social wasps and provide evidence for the role that elicitors play in inducing attractive odor blends.
- PublicationAccès libreTritrophic interactions : possible host-plants effects on the resistance of "Diabrotica" pests to natural enemies(2021)
; La sous-tribu Diabroticina de chrysomèles comprend de nombreux ravageurs importants des cultures agricoles et horticoles dans les Amériques, tels que le maïs et le concombre. L'une des espèces les plus dévastatrices, la chrysomèle des racines de maïs Diabrotica virgifera virgifera (WCR), est également un ravageur envahissant en Europe. Pour ce ravageur et les espèces de Diabrotica apparentées, le développement d'une lutte biologique efficace est nécessaire de toute urgence, et pour cela, des connaissances supplémentaires sur les interactions tri-trophiques entre Diabrotica, leurs plantes hôtes et leurs ennemis naturels sont nécessaires. Dans cette thèse, j’ai exploré les adaptations des ravageurs Diabrotica à leurs plantes hôtes avec leurs composés défensifs, et évalué l’éventuelle protection que les larves de Diabrotica obtiennent après l'ingestion de ces métabolites secondaires des plantes. Au cours d'échantillonnages sur le terrain au Mexique, j’ai observé que le parasitisme des coléoptères Diabroticina adultes par des parasitoïdes est minime (Chapitre I), mais j’ai constaté que les larves peuvent être infectées avec succès par des nématodes entomopathogènes (EPN) adaptés (Chapitre II). Des isolats d'EPN hautement infectieux collectés dans des champs de maïs mexicains pourraient être des candidats prometteurs pour contrôler WCR en Europe. Ces isolats et/ou leurs bactéries endosymbiotiques pourraient être adaptés à l'arsenal de défense déployé par les larves de WCR, qui comprend la séquestration des benzoxazinoïdes du maïs, mais des stratégies inconnues supplémentaires semblent également être impliquées. Les larves du généraliste Diabrotica balteata ne séquestrent pas des benzoxazinoïdes après s'être nourries des plantes de maïs et semblent moins capables de résister aux infections à EPN que les WCR. Cependant, elles sont capables de séquestrer des cucurbitacines après avoir mangé des plantes de concombre (Chapitre III). J'ai fourni des preuves solides que les larves de D. balteata peuvent transformer et séquestrer les cucurbitacines des plants de concombre. Cependant, je n'ai trouvé aucune preuve que les cucurbitacines séquestrées puissent protéger les larves de l'infection par des EPN, ni de l'attaque par des insectes prédateurs, des champignons entomopathogènes ou des bactéries. La performance des larves n'a pas non plus été affectée positivement par la teneur en cucurbitacines des tissus végétaux qu'elles ont consommées, d'où la signification adaptative de la séquestration de cucurbitacines reste à élucider. Curieusement, j’ai observé que les larves de D. balteata se nourrissent activement de tissus au-dessus de la surface, tels que tiges, cotylédons et feuilles, ce qui m’a incité à étudier si ce comportement procure des avantages et si d'autres espèces de Diabrotica ont un comportement similaire (Chapitre IV). Les larves de D. balteata, D. undecimpunctata et D. virgifera, normalement décrites comme larves de racines, se sont toutes avérées capables de se nourrir de feuilles ainsi que de racines de différentes plantes agricoles contenant des métabolites secondaires distincts. Pourtant, leurs performances et leur sensibilité à l'infection par des EPN n’ont pas été affectées différemment par le tissu que les larves avaient consommées. Ensemble, ces résultats contribuent à une meilleure compréhension de l'impact des métabolites secondaires des plante hôte ingérés par des insectes herbivores sur le troisième niveau trophique. Le succès des espèces de Diabrotica en tant que ravageurs des cultures semble être lié à leurs caractéristiques uniques pour survivre dans un environnement imprévisible en se nourrissant de différentes plantes et tissus, faisant face avec succès à une grande variété de composés de défense des plantes, qui dans certains cas peuvent fournir une protection contre les ennemis naturels. J’émet l'hypothèse que les larves de Diabrotica se nourrissant de maïs sont capables de détoxifier les benzoxazinoïdes, et discute de l'origine et de l'importance adaptative de la séquestration de cucurbitacines par les espèces de Diabrotica, qui ne semblerait pas liée à la défense contre les ennemis naturels. Enfin, les isolats d'EPN obtenus, ainsi que les nouvelles connaissances sur le comportement alimentaire des larves de Diabrotica rapportées dans cette thèse, contribueront, espérons-le, au développement de stratégies de biocontrôle nouvelles et efficaces contre les ravageurs du genre Diabrotica. ABSTRACT The subtribe Diabroticina of chrysomelid beetles includes many important pests of extensive and horticultural crops in the Americas, such as maize and cucumber. One of the most devastating species, the western corn rootworm Diabrotica virgifera virgifera (WCR), is also an invasive pest in Europe. For this and related Diabrotica pests, the development of efficient biological control is urgently needed, and for this further knowledge on tritrophic interactions of Diabrotica, their host plants and their natural enemies is required. In this thesis, I explored the adaptations of Diabrotica pests to their host plants and the plants’ defensive compounds, and evaluated the possible protection that Diabrotica larvae derive from ingesting these plant secondary metabolites. During field surveys in Mexico, I observed that parasitism of adult Diabroticina beetles by parasitoids is minimal (Chapter I), but found that the larvae can be successfully infected by adapted entomopathogenic nematodes (EPN) (Chapter II). Highly-infective EPN isolates collected in Mexican maize fields could be promising candidates to control the maizespecialist WCR in Europe. These isolates and/or their endosymbiotic bacteria may have adapted to the defense arsenal deployed by WCR larvae, which includes the sequestration of maize benzoxazinoids, but additional unknown strategies seem to be also involved. Larvae of the generalist Diabrotica balteata do not sequester benzoxazinoids after feeding on maize and seem to be less able to resist EPN infections than WCR. However, they are able to sequester cucurbitacins after feeding on cucumber plants (Chapter III). I provided strong evidence that D. balteata larvae can transformation and sequester cucurbitacins from cucumber plants. However, I found no evidence that the sequestered cucurbitacins can protect the larvae from infection by EPN, nor from the attack by insect predators, entomopathogenic fungi or bacteria. Larval performance was also not positively affected by cucurbitacin contents in plant tissues that they consumed, hence the adaptive significance of cucurbitacin sequestration remains to be unraveled. Surprisingly, the D. balteata larvae were observed to actively forage on aboveground tissues, which prompted us to study whether this behavior provides any benefits and if other Diabrotica species do the same (Chapter IV). Larvae of D. balteata, D. undecimpunctata and D. virgifera were all found to be able to feed on leaves as well as roots from different agricultural plants that contain distinct secondary metabolites. Yet, their performance and the susceptibility against EPN infection were not differentially impacted by the tissue that the larvae had fed on. Taken together, these results contribute to a better understanding of the impact of host plant secondary metabolites ingested by insect herbivores on the third trophic level. The success of Diabrotica species as crop pests seems to be related to their unique traits to survive in an unpredictable environment by feeding on different plants and tissues, successfully coping with a wide variety of plant defense chemicals, which in some cases may provide protection against natural enemies. I hypothesize that maize- feeding Diabrotica larvae may be able to detoxify benzoxazinoids, and discuss the origin and adaptive significance of cucurbitacin sequestration by Diabrotica species, which appears not to be related to defense against natural enemies. Finally, the isolates of EPN obtained, as well as the new insights on the aboveground feeding behavior by Diabrotica larvae reported in this thesis, will hopefully contribute to the development of novel and effective biocontrol strategies against Diabrotica pests. - PublicationAccès libreThe mate-seeking strategies of four braconid parasitoids (Hymenoptera: Braconidae)(2017)
- PublicationAccès libreThe role of indole in maize-herbivore interactions(2014)
; Afin de se protéger contre les attaques d’insectes herbivores, les plantes ont développé de multiples moyens de défense, dont la libération de composés volatils induits par les herbivores (HIPVs). Ces composés volatils peuvent être utilisés par les ennemis naturels des herbivores tels que les prédateurs et les parasitoïdes. D’autre part, ils peuvent être exploités par les herbivores eux-mêmes pour localiser leurs plantes hôtes. Certains HIPVs peuvent aussi avertir les tissus non attaqués d’une même plante ou les plantes voisines d’un risque d’attaque. Le terme employé est “priming”. Les plantes averties pourront ainsi répondre plus rapidement et de manière plus efficace lorsque l’attaque se produira. Tandis que certains HIPVs ont été bien étudiés, le rôle de beaucoup d’autre reste à trouver. Par exemple, nous n’avons que peu de connaissances en ce qui concerne l’indole, un composé dominant du mélange de volatils émis par les plantes. Dans la thèse présentée ici, nous avons étudié le rôle de l’indole dans les défenses directes et indirectes du maïs grâce à l’utilisation de plantes mutantes dans la production d’indole et d’indole synthétique.
Dans le premier chapitre, nous avons étudié le rôle de l’indole en tant que signal de défense. Nous fournissons la preuve que l’indole est essentiel pour le “priming” d’autres HIPVs au sein d’une même plante mais qu’il agit aussi comme signal de communication entre différentes plantes afin de les préparer à une possible attaque. Dans le deuxième chapitre, nous avons étudié l’effet de l’indole sur un insecte herbivore généraliste, Spodoptera littoralis. Nous démontrons que l’indole agit en tant de défense directe chez le maïs en repoussant les adultes et les chenilles de cette espèce et en réduisant la survie des chenille et le succès reproducteur des adultes. Dans le troisième chapitre, nous avons étudié l’importance de l’indole au niveau du troisième niveau trophique. Nous avons trouvé que malgré une attraction de certains parasitoïdes, une exposition à l’indole protège les chenilles de l’espèce S. littoralis en augmentant leur résistance contre les parasitoïdes. Dans le quatrième chapitre, nous avons étudié la spécificité des effets trouvés dans les deux chapitres précédents. Nous avons trouvé que ni le degré de spécialisation pour les plantes hôtes, ni l’origine phylogénétique, ni l’association avec des plantes produisantde l’indole ne déterminent la réponse des insectes herbivores et des ennemis naturels à l’indole. Nous concluons que le rôle de l’indole est dépendant des espèces.
D’une manière générale, cette thèse contribue à une meilleure compréhension du rôle de l’indole dans les intéractions entre les plantes, les insectes herbivores et les ennemis naturels; elle confirme le rôle multiple des composés volatils dans les intéractions tri-trophiques., In order to counter herbivore attacks, plants have developed a multitude of defence strategies, including the release herbivore-induced plant volatiles (HIPVs). HIPVs can be used as foraging cues by natural enemies of the herbivores, including predators and parasitoids. In addition, they can also be exploited by herbivores themselves to localize their host plants. Some HIPVs even prime non-attacked plant tissues or neighbouring plants to respond faster and more strongly to subsequent attacks. Whereas some HIPVs have been well studied, the role of many others remains unclear. For instance, little is known about indole, a major constituent of the herbivore-induced volatile blend. In the present thesis, we studied the role of indole in direct and indirect defences in maize using indole deficient mutants and synthetic indole.
In Chapter 1 we investigated the role of indole as a plant defence signal. We provide evidence that indole is essential for within-plant priming of other HIPVs and acts as a between-plant signal that primes non-attacked neighbours. In Chapter 2, we investigated the impact of indole on the generalist herbivore Spodoptera littoralis. We demonstrate that volatile indole acts as a direct defence in maize by repelling S. littoralis moths and caterpillars and by reducing the survival of early instar caterpillars and the reproductive output of adults. In Chapter 3, we studied the importance of indole on the third trophic level. We found that, although indole attracts certain parasitoids, indole-exposure protects S. littoralis caterpillars by increasing their resistance against parasitism. In Chapter 4, we investigated the specificity of the effects found in chapters 2 and 3. We found that neither the degree of host plant specialization nor the phylogenetic origin or the association with indole-producing plants determines the response of herbivores and natural enemies to the volatile, and that the role of indole is highly species-specific.
Overall, this thesis contributes to a better understanding of the role of indole in interactions between plants, herbivore insects and natural enemies and highlights the diverse roles of HIPVs in tritrophic interactions. - PublicationAccès libreSimultaneous feeding by aboveground and belowground herbivores attenuates plant-mediated attraction of their respective natural enemies(2007)
; 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. - PublicationAccès libreEvaluating the Induced-Odour Emission of a Bt Maize and its Attractiveness to Parasitic Wasps(2005)
; ; ; The current discussion on the safety of transgenic crops includes their effects on beneficial insects, such as parasitoids and predators of pest insects. One important plant trait to consider in this context is the emission of volatiles in response to herbivory. Natural enemies use the odours that result from these emissions as cues to locate their herbivorous prey and any significant change in these plant-provided signals may disrupt their search efficiency. There is a need for practical and reliable methods to evaluate transgenic crops for this and other important plant traits. Moreover, it is imperative that such evaluations are done in the context of variability for these traits among conventional genotypes of a crop. For maize and the induction of volatile emissions by caterpillar feeding this variability is known and realistic comparisons can therefore be made. Here we used a six-arm olfactometer that permits the simultaneous collection of volatiles emitted by multiple plants and testing of their attractiveness to insects. With this apparatus we measured the induced odour emissions of Bt maize (Bt11, N4640Bt) and its near-isogenic line (N4640) and the attractiveness of these odours to Cotesia marginiventris and Microplitis rufiventris, two important larval parasitoids of common lepidopteran pests. Both parasitoid species were strongly attracted to induced maize odour and neither wasp distinguished between the odours of the transgenic and the isogenic line. Also wasps that had previously experienced one of the odours during a successful oviposition divided their choices equally between the two odours. However, chemical analyses of collected odours revealed significant quantitative differences. The same 11 compounds dominated the blends of both genotypes, but the isogenic line released a larger amount of most of these. These differences may be due to altered resource allocation in the transgenic line, but it had no measurable effect on the wasps’ behaviour. All compounds identified here had been previously reported for maize and the differential quantities in which they were released fall well within the range of variability observed for other maize genotypes. - PublicationAccès libreIn Situ Modification of Herbivore-Induced Plant Odors : A Novel Approach to Study the Attractiveness of Volatile Organic Compounds to Parasitic Wasps(2004)
- PublicationAccès libreVariability in herbivore-induced odour emissions among maize cultivars and their wild ancestors (teosinte)(2001)
; Maize plants respond to caterpillar feeding with the release of relatively large amounts of specific volatiles, which are known to serve as cues for parasitoids to locate their host. Little is known about the genetic variability in such herbivore-induced plant signals and about how the emissions in cultivated plants compare to those of their wild relatives. For this reason we compared the total quantity and the qualitative composition of the odour blend among eleven maize cultivars and five wild Zea (Poaceae) species (teosinte), as well as among the offspring of eight Zea mays mexicana plants from a single population. Young plants were induced to release volatiles by mechanically damaging the leaves and applying oral secretions of Spodoptera littoralis (Lepidoptera: Noctuidae) caterpillars to the wounded sites. Volatiles were collected 7 h after treatment and subsequently analysed by gas chromatography. The total amounts of volatiles released were significantly different among maize cultivars as well as among the teosintes. Moreover, striking differences were found in the composition of the induced odour blends. Caryophyllene, for instance, was released by some, but not all varieties and teosintes, and the ratios among monoterpenes and sesquiterpenes varied considerably. The offspring of different mother plants of the Z. m. mexicana population showed some variation in the total amounts that they released, but the composition of the odour blend was very consistent within the population of this teosinte species. We discuss the ecological significance of these findings in terms of specificity and reliability of induced plant signals for parasitoids. - PublicationAccès libreCombined use of herbivore-induced plant volatiles and sex pheromones for mate location in braconid parasitoids
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