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Turlings, Ted

Nom
Turlings, Ted
Affiliation principale
Fonction
Professeur.e ordinaire
Email
ted.turlings@unine.ch
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https://libra.unine.ch/handle/123456789/330
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0000-0002-8315-785X

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  • Publication
    Accès libre
    Ecological impact of the invasive horse-chestnut leaf miner, "Cameraria ohridella" Deschka & Dimic (Lepidoptera: Gracillariidae) on native species
    (2009)
    Péré, Christelle
    ;
    Turlings, Ted 
    La mineuse du marronnier d’Inde, Cameraria ohridella, est la première mineuse et le premier ravageur important attaquant le marronnier à fleurs blanches, Aesculus hippocastanum, natif des Balkans et introduit en Europe Centrale en tant qu’arbre ornemental. Le papillon, probablement originaire aussi des Balkans, a été découvert pour la première fois en Macédoine, en 1984, et s’est depuis répandu dans toute l’Europe (Chapitre 1). Cette thèse est la première tentative d’évaluation de l’impact écologique d’une mineuse exotique et invasive sur la faune et la flore natives. Cameraria ohridella est attaquée par plusieurs espèces natives de parasitoïdes et prédateurs. Le premier objectif de cette thèse était d’évaluer les interactions de C. ohridella avec les espèces de mineuses natives à travers le partage d’ennemis naturels communs, et en particulier les parasitoïdes. Cet impact indirect est connu sous le nom de "compétition apparente". En dépit du faible taux de parasitisme observé chez C. ohridella, les populations du papillon sont tellement importantes qu’un grand nombre de parasitoïdes, considérés comme polyphages, sont produits deux à quatre fois par an. Ces parasitoïdes ont alors la possibilité d’attaquer d’autres espèces de mineuses et, par conséquent, affecter leur densité, tout particulièrement au printemps. En effet, après la diapause, les parasitoïdes émergent des feuilles mortes de marronnier en même temps, voire plus tôt, que leur hôte et, au moins cinq semaines avant que les larves âgées et les chrysalides de C. ohridella soient disponibles. Nos résultats ont montré que la richesse spécifique et l’abondance des mineuses natives étaient plus basses à proximité de marronniers infestés par C. ohridella comparé aux sites de contrôle (Chapitre 2). Cependant, aucune évidence de compétition apparente n’a été trouvée entre C. ohridella et le charançon du hêtre, Orchestes fagi, dont la mortalité totale, le parasitisme et la prédation n’étaient pas significativement différents en présence et en absence de marronniers infestés. Plusieurs espèces de parasitoïdes attaquant communément C. ohridella ont été élevées sur O. fagi, mais en général, leur densité n’était pas plus importante à proximité de marronniers infestés. Des explications plausibles pour expliquer ces résultats inattendus sont fournies (Chapitre 3). En Europe, des mines de C. ohridella ont également été trouvées sur deux espèces d’érables natifs, Acer pseudoplatanus (érable sycomore) et Acer platanoides (érable plane), mais les taux d’attaques sont très variables. Le second objectif de cette thèse était de fournir une synthèse de la relation trophique entre C. ohridella et A. pseudoplatanus et, d’évaluer la possibilité d’un changement d’hôte de C. ohridella vers A. pseudoplatanus. Nos résultats ont montré qu’un grand nombre d’œufs sont pondus sur A. pseudoplatanus situés à proximité de marronniers infestés et, que la majorité des larves meurt aux jeunes stades. Par contre, il n’y a pas d'évidence que le niveau d’attaque augmente avec le temps, en Europe. Des observations sur le terrain, des études expérimentales d’exposition de jeunes arbres d’A. pseudoplatanus et, des essais d’élevage dans un jardin commun ont montré que les érables sycomores pouvaient varier individuellement dans leur sensibilité face à C. ohridella, tandis qu’il n’y avait pas d’évidence que les populations de C. ohridella varient dans leur performance sur A. pseudoplatanus. Par conséquent, les populations de C. ohridella ne représentent pas, à court terme, un risque majeur pour A. pseudoplatanus (Chapitre 4). De manière générale, cette thèse fournit un des premiers exemples suggérant que les insectes invasifs peuvent affecter indirectement les espèces d’insectes natifs via la compétition apparente. De plus, cette thèse est une importante contribution à la connaissance de l’écologie de C. ohridella car elle fournit les premières informations détaillées de la relation trophique entre C. ohridella et A. pseudoplatanus., The horse-chestnut leaf miner, Cameraria ohridella, is the first leaf miner and first major pest known to attack the white flowering horse-chestnut tree, Aesculus hippocastanum, native to the Balkans and introduced in Central Europe as an ornamental urban tree. This moth, which probably originates from the Balkans, was first discovered in Macedonia in 1984 and has since invaded most of Europe (Chapter 1). This thesis is the first attempt to investigate the ecological impact of an invasive alien leaf miner on native fauna and flora. Cameraria ohridella is attacked by several European parasitoids and predators. The first aim of this thesis was to assess the interactions of C. ohridella with native leaf miner species through their shared natural enemies, and in particular, parasitoids. This indirect impact is known as apparent competition. Despite the low parasitism rates observed in C. ohridella, populations are so high that an unusual number of polyphagous parasitoids is produced two to four times per year. These parasitoids then have the opportunity to attack other leaf miners and, consequently, affect their density, especially in spring. After overwintering, the parasitoids emerge from dead leaves of horse-chestnut at the same time as, or earlier than, their host, and at least five weeks before suitable C. ohridella larvae or pupae are available. Our results showed that species richness and abundance of native leaf miners were lower in the vicinity of horse-chestnut trees infested by C. ohridella compared to control sites (Chapter 2). However, no evidence for apparent competition was found between C. ohridella and the native beech leaf mining weevil, Orchestes fagi, as total mortality, parasitism and predation were not significantly different. Several parasitoid species commonly attacking C. ohridella were reared from O. fagi, but, in general, their density was not higher in the vicinity of infested horse-chestnut trees. Possible explanations for these unexpected results are provided (Chapter 3). In Europe, mines of C. ohridella have also been recorded on two native maple species, Acer pseudoplatanus and Acer platanoides, but attacks are highly variable. The second aim of this thesis was to provide an overview of the relationship between C. ohridella and A. pseudoplatanus and to assess the possibility of a host shift by C. ohridella to A. pseudoplatanus. So far, our results have shown that high numbers of eggs are laid on A. pseudoplatanus when the trees are surrounded by horse-chestnut and that the majority of the larvae died in the first two instars. Our outcomes also showed that there is no clear indication that the level of attack increases with time in Europe. Field observations, experimental exposure of A. pseudoplatanus saplings and rearing trials in a common garden study showed that individual trees may vary in their susceptibility to C. ohridella, whereas there was no evidence that C. ohridella populations vary in their performance on A. pseudoplatanus. Thus far, there is little evidence that C. ohridella represents a major risk for A. pseudoplatanus (Chapter 4). Overall the present thesis provides, to our knowledge, one of the first examples suggesting that invasive alien insects may indirectly affect native species of insect through apparent competition. Moreover, this thesis is an important contribution to the knowledge of the ecology of C. ohridella because it provides the first detailed information on the relationship between C. ohridella and A. pseudoplatanus.
  • Publication
    Accès libre
    Identification of seven species of hymenopteran parasitoids of Spodoptera frugiperda, using polymerase chain reaction amplification and restriction enzyme digestion
    (2008)
    Jourdie, Violaine
    ;
    Alvarez, Nadir
    ;
    Turlings, Ted 
    1 The fall armyworm Spodoptera frugiperda is a voracious pest of numerous crops of economic importance throughout the New World. In its native Mexico, larvae can be attacked by several species of parasitic wasps, which are candidate biological control agents against this and other lepidopteran pests.
    2 We attempted to survey the parasitoid fauna on S. frugiperda in maize and sorghum fields throughout Mexico. However, our efforts have been hampered by the incomplete development of parasitoid larvae emerging from collected Spodoptera caterpillars.
    3 This problem was solved by developing a method to identify seven species of parasitic wasps using polymerase chain reaction amplification and restriction enzyme digestion. This enables the precise determination of the species of those parasitoid larvae that are usually not morphologically identifiable.
  • Publication
    Accès libre
    Parasotoid communities and genetic structure: host plant does not matter
    (2008)
    Jourdie, Violaine
    ;
    Turlings, Ted 
    Plant-insect interactions have long been studied and reveal intricate mechanisms. Plants are capable of defending themselves both directly by poisoning insect herbivores and indirectly by emitting volatile compounds that are used by the natural enemies to localize their host. In response, insects have evolved strategies to defeat plant defense mechanisms. Because insect pests are affected by plant signals, their natural enemies also bear these effects. As host plant can affect the physiology and behavior of parasitoids, it may also contribute to shaping their population genetic structure. This thesis mainly aimed to investigate the effects of host plant on the population genetics of parasitoids of the fall armyworm (FAW), Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae), using microsatellite markers. The FAW is one of the New World’s most devastating pests and it attacks several economically important crops as well as grasses. It is commonly controlled by chemical insecticides. However, as it is attacked by numerous parasitoids species, and in order to limit the use of toxic pesticides, biological control is a safer alternative mean of management for this pest. The success of biological control relies on a good knowledge of the system, hence the importance of investigating population genetics and communities structure. This study focused on two primary parasitoids of S. frugiperda, Chelonus insularis Cresson (Hymenotera: Braconidae) and Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae). It was conducted on two host plants, maize and sorghum, in Mexico where maize originated and where sorghum was introduced barely over a century ago. Due to difficulties encountered during sampling, whereby immature parasitoids did not complete their life cycle and therefore could not be morphologically identified, a technique was first developed, as a cheaper and faster alternative to sequencing, to molecularly assign parasitoid larvae to species. This simple but nonetheless efficient technique consists in amplifying DNA through polymerase chain reaction and digesting it with a cocktail of restriction endonucleases in order to obtain a species specific pattern when the digestion product is run on an agarose gel. With this technique, we could get an accurate estimation of which species were collected and in what proportions, which allowed to study parasitoid community structure. The study of population genetics first required the development and optimization of reliable molecular markers. Fifteen and 13 highly polymorphic microsatellites were respectively isolated from C. sonorensis and from C. insularis. These markers were used to investigate fine-scale genetic structure in Mexican populations. We could discern a regional effect, but host plant seems to play no role in shaping the populations genetic structure. High levels of admixture indicate that gene flow between populations is considerable. Finally, genetic structure was investigated at larger scale through a phylogeography using sequences of mitochondrial and nuclear marker genes. The lack of local structure was confirmed for both species. We found however evidence for North-South migration through a single colonization event in C. insularis, and a cryptic species distributed in Canada was discovered. Dispersal of these insects seems to be largely driven by wind as suggested by genetic similarities between geographically very distant individuals.
  • Publication
    Accès libre
    Differential Attractiveness of Induced Odors Emitted by Eight Maize Varieties for the Parasitoid Cotesia marginiventris : Is Quality or Quantity Important ?
    (2002)
    Hoballah, Maria Elena
    ;
    Tamò, Cristina
    ;
    Turlings, Ted 
    Herbivore-induced plant volatiles can function as indirect defense signals that attract natural enemies of herbivores. Several parasitoids are known to exploit these plant-provided cues to locate their hosts. One such parasitoid is the generalist Cotesia marginiventris, which is, among others, attracted to maize volatiles induced by caterpillar damage. Maize plants can be induced to produce the same blend of attractive volatiles by treating them with regurgitant of Spodoptera species. We collected and analyzed the regurgitant-induced emissions of two plant species (cowpea and maize) and of eight Mexican maize varieties and found significant differences among their volatile emissions, both in terms of total quantity and the quality of the blends. In a Y-tube olfactometer, the odors of the same artificially induced plant species and Mexican varieties were offered in dual choice experiments to naïve mated females of C. marginiventris. Wasps preferred cowpea over maize odor and, in 3 of 12 combinations with the maize varieties, they showed a preference for the odors of one of the varieties. A comparison of the odor collection with results from the behavioral assays indicates that not only the quantity of the volatile emissions, but also the quality composition of the volatile blends is important for attraction of C. marginiventris. The results are discussed in the context of the possibility of breeding crop varieties that are particularly attractive to parasitoids.
  • Publication
    Accès libre
    Host stage preference and sex allocation in Aenasius vexans, an encyrtid parasitoid of the cassava mealybug
    (2000)
    Bertschy, Catherine
    ;
    Turlings, Ted 
    ;
    Bellotti, Anthony
    ;
    Dorn, Silvia
    The solitary endoparasitoid Aenasius vexans Kerrich (Hymenoptera: Encyrtidae) is used for augmentative releases against the cassava mealybug, Phenacoccus herreni Cox & Williams (Sternorrhyncha: Pseudococcidae), an important pest on cassava in South America. In light of the need for large numbers of high quality females, experiments were conducted on host stage suitability and sex allocation. In choice and no-choice experiments, individual female wasps were offered second and third instar, as well as adult, hosts. During the first five days after emergence, the wasps showed a steady increase in the number of hosts they successfully parasitised per day, but the respective secondary sex ratio for each instar remained constant. Parasitism was highest for third instar hosts in no-choice tests, while in choice tests parasitism was highest in both third instars and adults. The later the developmental stage of the host at oviposition, the faster the parasitoids developed and emerged, and for each host stage, the development time of males was shorter than for females. The sex ratio of the wasps emerging from hosts that were parasitised as second instars was strongly male-biased, while the apparently preferred later stages yielded significantly more females than males. Female and male A. vexans emerging from hosts parasitised at the third instar were significantly larger than for the other stages. This may explain the preference for the third instar as well as the female-biased sex ratio, as size is usually positively correlated with higher fitness, especially in females. The results suggest that third instar hosts are the most suitable for rearing high numbers of large females.
  • Publication
    Accès libre
    Role of plant volatiles in host location by the specialist parasitoid Microplitis croceipes cresson (Braconidae: Hymenoptera)
    (1993)
    McCall, Philip J.
    ;
    Turlings, Ted 
    ;
    Lewis, W. Joe
    ;
    Tumlinson, James H.
    A study was conducted to determine the primary source of volatile cues within the plant-host complex used by hostseeking freeflying female Microplitis cro-ceipesCresson in flight tunnel bioassays. In single-source and two-choice tests, using wasps given an oviposition experience on either cotton (Gossypium hirsutum) or cowpea (Vigna unguiculata) seedlings damaged by corn earworm (CEW; Helicoverpa zea Boddie), the damaged seedlings were significantly more attractive than the CEW frass, which was in turn more attractive than the larvae themselves. In a series of two-choice wind-tunnel tests, the discriminatory ability of the wasps was examined, following various oviposition experiences. Significantly more wasps flew to plants with old damage than to plants with fresh damage, regardless of whether they had experience on fresh or old damage. In a comparison of plant species, wasps with only one experience on either hostdamaged cotton or host-damaged cowpea were unable to distinguish between them, and showed no preference for either plant, whereas wasps with multiple experiences on a particular plant preferentially flew to that plant in the choice test. In comparing hosts with nonhosts, wasps successfully learned to distinguish CEW from beet armyworm (BAW; Spodoptera exigua) on cotton but were unable to distinguish CEW from either BAW or cabbage looper (Trichoplusia ni) on cowpea. The results show the important role played by plant volatiles in the location of hosts by M. croceipesand indicate the wasps limitations in discriminating among the various odors. The ecological advantages and disadvantages of this behavior are discussed.
  • Publication
    Accès libre
    Isolation and identification of allelochemicals that attract the larval parasitoid, Cotesia marginiventris (Cresson), to the microhabitat of one of its hosts
    (1991)
    Turlings, Ted 
    ;
    Tumlinson, James H.
    ;
    Heath, Robert R.
    ;
    Proveaux, Adron T.
    ;
    Doolittle, Robert E.
    Volatiles released from corn seedlings on which beet armyworm larvae were feeding were attractive to females of the parasitoid, Cotesia marginiventris (Cresson), in flight tunnel bioassays. Analyses of the collected volatiles revealed the consistent presence of 11 compounds in significant amounts. They were: (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)- 3-hexen-1-yl acetate, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, indole, α-trans-bergamotene, (E)-β-farnesene, (E)-nerolidol, and (3E,7E)-4,8,12-trimethyl-1, 3,7,ll-tridecatetraene. A synthetic blend of all 11 compounds was slightly less attractive to parasitoid females than an equivalent natural blend. However, preflight experience with the synthetic blend instead of experience with a regular plant-host complex significantly improved the response to the synthetic blend. Our results suggest that C. marginiventris females, in their search for hosts, use a blend of airborne semiochemicals emitted by plants on which their hosts feed. The response to a particular odor blend dramatically increases after a parasitoid experiences it in association with contacting host by-products.