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The role of indole and other shikimic acid derived maize volatiles in the attraction of two parasitic wasps

Marco D'Alessandro, Matthias Held, Yann Triponez & Ted Turlings

Résumé 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.
   
Mots-clés Cotesia marginiventris, Microplitis rufiventris, Spodoptera littoralis, Zea mays, parasitoids, Volatile Organic Compounds (VOCs), Herbivore-Induced Plant Volatiles (HIPVs), host location, associative, learning, tritrophic interactions, indole, shikimic acid, glyphosate, induced defenses, INDUCED PLANT ODORS, ZEA-MAYS, JASMONIC ACID, SPODOPTERA-EXIGUA, INSECT, HERBIVORY, INFOCHEMICAL USE, ORAL SECRETION, PREDATORY MITE, EMISSION, DEFENSE
   
Citation D'Alessandro, M., Held, M., Triponez, Y., & Turlings, T. (2006). The role of indole and other shikimic acid derived maize volatiles in the attraction of two parasitic wasps. Journal of Chemical Ecology, 32(12), 2733-2748.
   
Type Article de périodique (Anglais)
Date de publication 2006
Nom du périodique Journal of Chemical Ecology
Volume 32
Numéro 12
Pages 2733-2748