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Held, Matthias

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Held, Matthias
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https://libra.unine.ch/handle/123456789/598

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  • Publication
    Métadonnées seulement
    Attractiveness of constitutive and herbivore-induced sesquiterpene blends of maize to the parasitic wasp
    (2011)
    Fontana, A.
    ;
    Held, Matthias 
    ;
    Fantaye, C. A.
    ;
    Turlings, Ted 
    ;
    Degenhardt, Jörg
    ;
    Gershenzon, Jonathan
    Plant volatile compounds induced by herbivore attack have been demonstrated to provide a signal to herbivore enemies such as parasitic wasps that use these volatiles to locate their hosts. However, in addition to herbivore-induced volatiles, plants often release volatiles constitutively. We assessed the interaction between herbivore-induced and constitutively released volatiles of maize in the attraction of the wasp Cotesia marginiventris that parasitizes herbivorous lepidopteran larvae feeding on maize. Experiments were carried out with olfactometers in which the sources of volatiles were transgenic Arabidopsis thaliana plants overexpressing maize sesquiterpene synthases that produce blends of herbivore-induced or constitutive compounds. We found that the constitutive volatiles of maize terpene synthase 8 (TPS8) were attractive to C. marginiventris, just like the herbivore-induced volatiles of TPS10 studied earlier. A mixture of both the TPS8 and TPS10 volatile blends, however, was more effective in parasitoid attraction, indicating that constitutively released sesquiterpenes enhance the attraction of those induced by herbivores. While C. marginiventris did not distinguish among the volatiles of TPS8, TPS10, nor those of another maize sesquiterpene synthase (TPS5), when these blends were combined, their attractiveness to the wasp appeared to increase with the complexity of the blend.
  • Publication
    Métadonnées seulement
    The role of indole and other shikimic acid derived maize volatiles in the attraction of two parasitic wasps
    (2006)
    D'Alessandro, Marco
    ;
    Held, Matthias 
    ;
    Triponez, Yann
    ;
    Turlings, Ted 
    After herbivore attack, plants release a plethora of different volatile organic compounds (VOCs), which results in odor blends that are attractive to predators and parasitoids of these herbivores. VOCs in the odor blends emitted by maize plants (Zea mays) infested by lepidopteran larvae are well characterized. They are derived from at least three different biochemical pathways, but the relative importance of each pathway for the production of VOCs that attract parasitic wasps is unknown. Here, we studied the importance of shikimic acid derived VOCs for the attraction of females of the parasitoids Cotesia marginiventris and Microplitis rufiventris. By incubating caterpillar-infested maize plants in glyphosate, an inhibitor of the 5-enolpyruvylshikimate-3-phospate (EPSP) synthase, we obtained induced odor blends with only minute amounts of shikimic acid derived VOCs. In olfactometer bioassays, the inhibited plants were as attractive to naive C. marginiventris females as control plants that released normal amounts of shikimic acid derived VOCs, whereas naive M. rufiventris females preferred inhibited plants to control plants. By adding back synthetic indole, the quantitatively most important shikimic acid derived VOC in induced maize odors, to inhibited plants, we showed that indole had no effect on the attraction of C. marginiventris and that M. rufiventris preferred blends without synthetic indole. Exposing C. marginiventris females either to odor blends of inhibited or control plants during oviposition experiences shifted their preference in subsequent olfactometer tests in favor of the experienced odor. Further learning experiments with synthetic indole showed that C. marginiventris can learn to respond to this compound, but that this does not affect its choices between natural induced blends with or without indole. We hypothesize that for naive wasps the attractiveness of an herbivore-induced odor blend is reduced due to masking by nonattractive compounds, and that during oviposition experiences in the presence of complex odor blends, parasitoids strongly associate some compounds, whereas others are largely ignored.