Abstract
Plants produce distinct blends of volatile compounds that attract pollinators (floral odors) or natural enemies of insect herbivores (herbivore-induced plant volatiles). The admixture of these blends in the atmosphere may alter the attraction of insect mutualists and ultimately affect plant fitness. Here, using synthetic blends of Brassica rapa floral volatiles and real B. rapa flowers, we investigated how floral odors impact the foraging behavior of parasitoids. In an olfactometer setting, floral odors reduced the attractiveness of plants infested by herbivores to parasitoids by 43.5% and affected four out of five parasitoid species tested. Additionally, experiments with the parasitoid Cotesia glomerata revealed that the effects of floral odors are dose-dependent and that floral odors were less disruptive under wind tunnel conditions than under olfactometer conditions. Electroantennogram recordings showed that C. glomerata antennae do respond to floral compounds, but that floral compounds do not inhibit antennal responses to herbivore-induced leaf volatiles. In conclusion, floral odors can act as background pollutants decreasing the attractiveness of chemical blends used by natural enemies to locate their hosts. Under natural conditions, such interferences could affect the outcome of tritrophic interactions and may play an important role in the evolution of plant volatile signaling.
Highlights
Plants produce and release an immense diversity of volatile organic compounds (VOCs) into the atmosphere (Dudareva et al, 2006; Raguso, 2008; Mumm and Dicke, 2010)
It is thought that some herbivore-induced plant volatiles (HIPVs) have evolved as a means to attract natural enemies, which in turn fend off plant attackers and reduce herbivore damage (Dicke and Loon, 2000; Turlings and Wäckers, 2004; Turlings and Erb, 2018)
In a previous study involving the plant B. rapa L. (Brassicaceae), the specialist herbivore Pieris brassicae L. (Lepidoptera: Pieridae), and its main parasitoid Cotesia glomerata L. (Hymenoptera: Braconidae), we found that floral odors directly decrease the attractiveness of herbivore-infested plants to C. glomerata (Desurmont et al, 2015)
Summary
Plants produce and release an immense diversity of volatile organic compounds (VOCs) into the atmosphere (Dudareva et al, 2006; Raguso, 2008; Mumm and Dicke, 2010). It is thought that some herbivore-induced plant volatiles (HIPVs) have evolved as a means to attract natural enemies (i.e., predators and Floral Odors Disrupt Parasitoid Behavior parasitoids), which in turn fend off plant attackers and reduce herbivore damage (Dicke and Loon, 2000; Turlings and Wäckers, 2004; Turlings and Erb, 2018). This type of indirect plant defense has received extensive scientific attention (Godfray, 1994; Wajnberg et al, 2008) the fitness benefits plants gain from attracting natural enemies are not easy to demonstrate (Allison and Hare, 2009; Hare, 2011; Kessler and Heil, 2011; Kaplan, 2012b). Floral odors and HIPVs can involve common, ubiquitous compounds or, on the contrary, highly specific compounds or ratios of compounds (Dudareva et al, 2006; Heil, 2014), And their admixture may affect the behavioral response of receiving organisms (Kessler and Halitschke, 2009; Randlkofer et al, 2010; Desurmont et al, 2015)
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