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Laplanche, Diane
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Laplanche, Diane
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- PublicationAccès libreEvolutionary changes in an invasive plant support the defensive role of plant volatiles(2021-10-29)
; ; ; ; Desurmont, Gaylord A.It is increasingly evident that plants interact with their outside world through the production of volatile organic compounds, but whether the volatiles have evolved to serve in plant defense is still a topic of considerable debate.Unharmed leaves constitutively release small amounts of volatiles, but when the leaves are damaged by herbivorous arthropods, they emit substantially more volatiles. These herbivore-induced plant volatiles (HIPVs) attract parasitoids and predators that kill insect herbivores, and this can benefit the plants.As yet, however, there is no tangible evolutionary evidence that this tritrophic interplay contrib- utes to the selection forces that have shaped the volatile emissions of plants.With this in mind, we investigated the evolutionary changes in volatile emissions in invasive common ragwort and the respective defensive roles of its constitutive and inducible volatiles. This Eurasian plant has invaded other continents, where it evolved for many generations in the absence of specialized herbivores and their natural enemies. We found that, compared to native ragworts, invasive plants release higher levels of constitutive volatiles but considerably lower levels of herbivore-induced volatiles. As a consequence, invasive ragwort is more attractive to a specialist moth but avoided by an unadapted generalist moth. Importantly, conforming to the indirect defense hypothesis, a specialist parasitoid was much more attracted to caterpillar-damaged native ragwort, which was reflected in higher parasitism rates in a field trial. The evolution of foliar volatile emissions appears to be indeed driven by their direct and indirect roles in defenses against insects. - PublicationMétadonnées seulementImpact of exotic insect herbivores on native tritrophic interactions: a case study of the African cotton leafworm,(2014)
; ; ; Desurmont, Gaylord A.1. When exotic herbivores invade new environments, they have the potential to interfere with native predator-prey relationships. This interference can be indirect, via changes induced in native host plants, and may have cascading consequences at the community level. Here we investigate the impact of the presence of an exotic generalist insect herbivore, the African cotton leafworm Spodoptera littoralis, on the outcome of native tritrophic interactions between the plant Brassica rapa, the herbivore Pieris brassicae, and its parasitoid Cotesia glomerata. 2. In olfactometer choice-tests, plants damaged by S. littoralis and plants damaged by both S. littoralis and P. brassicae were consistently less attractive to the parasitoid than plants damaged by P. brassicae alone. Chemical analyses revealed that B. rapa volatiles typically induced by S. littoralis dominated the headspace in case of dual herbivore infestation. 3. In behavioral observations in petri dishes, C. glomerata wasps mistakenly attacked S. littoralis larvae significantly more often when P. brassicae was present, and attacks on both herbivores were comparable in terms of time (attack duration) and energy investment (number of eggs injected). Successful parasitism of S. littoralis was never observed, but larvae exposed to C. glomerata for 24 hours exhibited reduced survivorship, possibly as a result of failed parasitism attempts. 4. In tents with herbivore-infested B. rapa plants, the presence of S. littoralis did not have an effect on the parasitism rates of P. brassicae by C. glomerata, regardless of whether the two species were on the same or on different plants. Field experiments in newly invaded environments are necessary to evaluate the realized impact of S. littoralis. 5. Synthesis. Our study illustrates that exotic herbivores can impact native tritrophic interactions associated with Brassica rapa, even if they cannot be used as prey by native natural enemies. The mechanisms behind such effects, in particular chemical interference with foraging cues via changes in herbivore-induced plant volatiles, have the potential to be quite general, and their long-term effects on native communities should not be underestimated. This article is protected by copyright. All rights reserved. - PublicationMétadonnées seulementMaking the right call at the right time: ontogeny-dependent dynamics of attractiveness to natural enemies in(2014)
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