Impact of exotic insect herbivores on native tritrophic interactions: a case study of the African cotton leafworm, Spodoptera littoralis and insects associated with the field mustard Brassica rapa. (January 2015)

• Record Type: Journal Article
• Authors: Chabaane, Yosra; Laplanche, Diane; Turlings, Ted C. J.; Desurmont, Gaylord A.; Phillips, Ryan
• Is Part Of: Journal of ecology. Volume 103:Number 1(2015:Jan.)
• Page Start: 109
• Page End: 117
• Publication Date: 2015-01
• Subjects: Plant ecology -- Periodicals; 577.05
• DOI: 10.1111/1365-2745.12304
• Languages: English
• ISSNs: 0022-0477

Abstract

<abstract abstract-type="main" id="jec12304-abs-0001"> <title>Summary</title> <p> <list id="jec12304-list-0001" list-type="order"> <list-item> <p>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 <italic>Spodoptera littoralis</italic>, on the outcome of native tritrophic interactions between the plant <italic>Brassica rapa</italic>, the herbivore <italic>Pieris brassicae</italic> and its parasitoid <italic>Cotesia glomerata</italic>.</p> </list-item> <list-item> <p>In olfactometer choice tests, plants damaged by <italic>S. littoralis</italic> and plants damaged by both <italic>S. littoralis</italic> and <italic>P. brassicae</italic> were consistently less attractive to the parasitoid than plants damaged by <italic>P. brassicae</italic> alone. Chemical analyses revealed that <italic>B. rapa</italic> volatiles typically induced by <italic>S. littoralis</italic> dominated the headspace in case of dual herbivore infestation.</p> </list-item> <list-item> <p>In behavioural observations in petri dishes, <italic>C. glomerata</italic> wasps mistakenly attacked <italic>S. littoralis</italic> larvae significantly more often when <italic>P. brassicae</italic> 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 <italic>S. littoralis</italic> was never observed, but larvae exposed to <italic>C. glomerata</italic> for 24 h exhibited reduced survivorship, possibly as a result of failed parasitism attempts.</p> </list-item> <list-item> <p>In tents with herbivore‐infested <italic>B. rapa</italic> plants, the presence of <italic>S. littoralis</italic> did not have an effect on the parasitism rates of <italic>P. brassicae</italic> by <italic>C. glomerata</italic>, 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 <italic>S. littoralis</italic>.</p> </list-item> <list-item> <p> <italic>Synthesis</italic>. Our study illustrates that exotic herbivores can impact native tritrophic interactions associated with <italic>Brassica rapa</italic>, 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.</p> </list-item> </list> </p> </abstract>