Complex Odor from Plants under Attack: Herbivore's Enemies React to the Whole, Not Its Parts

Michiel Van Wijk,Maurice W Sabelis,Paulien J A De Bruijn

doi:10.1371/journal.pone.0021742

Michiel Van Wijk, Maurice W Sabelis + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0021742

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Journal: PloS one	Publication Date: Jul 13, 2011
Citations: 92	License type: CC BY 4.0

Affiliation: University of Amsterdam

Abstract

BackgroundInsect herbivory induces plant odors that attract herbivores' natural enemies. Assuming this attraction emerges from individual compounds, genetic control over odor emission of crops may provide a rationale for manipulating the distribution of predators used for pest control. However, studies on odor perception in vertebrates and invertebrates suggest that olfactory information processing of mixtures results in odor percepts that are a synthetic whole and not a set of components that could function as recognizable individual attractants. Here, we ask if predators respond to herbivore-induced attractants in odor mixtures or to odor mixture as a whole.Methodology/Principal FindingsWe studied a system consisting of Lima bean, the herbivorous mite Tetranychus urticae and the predatory mite Phytoseiulus persimilis. We found that four herbivore-induced bean volatiles are not attractive in pure form while a fifth, methyl salicylate (MeSA), is. Several reduced mixtures deficient in one component compared to the full spider-mite induced blend were not attractive despite the presence of MeSA indicating that the predators cannot detect this component in these odor mixtures. A mixture of all five HIPV is most attractive, when offered together with the non-induced odor of Lima bean. Odors that elicit no response in their pure form were essential components of the attractive mixture.Conclusions/SignificanceWe conclude that the predatory mites perceive odors as a synthetic whole and that the hypothesis that predatory mites recognize attractive HIPV in odor mixtures is unsupported.

Highlights

Since the discovery that plants release herbivore-induced plant volatiles (HIPV) and thereby recruit predatory arthropods, researchers have sought ways to harness this chemical communication system
(MeSA, b-ocimene, cis-3-hexenyl acetate, TMTT and DMNT) in addition to the odor of a Lima bean leaf disc was attractive to P. persimilis (Gt df = 6 = 21.70 P = 0.001, Gp df = 1 = 18.34 P = 0.000, Gh df = 5 = 3.35 P = 0.645, Figure 1)
Facing this more realistic choice, the predatory mites preferred the artificial mixture over the odor of non-infested Lima bean to an extent similar as they prefer the natural odor of spider-mite-infested Lima bean over the odor of non-infested Lima bean (Figure 1)

Summary

Introduction

Since the discovery that plants release herbivore-induced plant volatiles (HIPV) and thereby recruit predatory arthropods, researchers have sought ways to harness this chemical communication system. This led to a search for individual HIPV that act as predator attractants [1]. If predatory arthropods perceive odor mixtures as collections of classifiable chemical components that function as ‘‘attractant’’ or ‘‘repellent’’ it should be possible to manipulate the distribution of predatory arthropods in the environment through manipulation of HIPV This possibility gained support from experiments wherein transgenic plants that constitutively produced (3S)-(E)-nerolidol were preferred by predators over non-transgenic control plants [2].

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