Variation in natural plant products and the attraction of bodyguards involved in indirect plant defenseThe present review is one in the special series of reviews on animal–plant interactions.

Abstract

Plants can respond to feeding or egg deposition by herbivorous arthropods by changing the volatile blend that they emit. These herbivore-induced plant volatiles (HIPVs) can attract carnivorous natural enemies of the herbivores, such as parasitoids and predators, a phenomenon that is called indirect plant defense. The volatile blends of infested plants can be very complex, sometimes consisting of hundreds of compounds. Most HIPVs can be classified as terpenoids (e.g., (E)-β-ocimene, (E,E)-α-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene), green leaf volatiles (e.g., hexanal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate), phenylpropanoids (e.g., methyl salicylate, indole), and sulphur- or nitrogen-containing compounds (e.g., isothiocyanates or nitriles, respectively). One highly intriguing question has been which volatiles out of the complex blend are the most important ones for the carnivorous natural enemies to locate "suitable host plants. Here, we review the methods and techniques that have been used to elucidate the carnivore-attracting compounds. Electrophysiological methods such as electroantennography have been used with parasitoids to elucidate which compounds can be perceived by the antennae. Different types of elicitors and inhibitors have widely been applied to manipulate plant volatile blends. Furthermore, transgenic plants that were genetically modified in specific steps in one of the signal transduction pathways or biosynthetic routes have been used to find steps in HIPV emission crucial for indirect plant defense. Furthermore, we provide an overview on biotic and abiotic factors that influence the emission of HIPVs and how this can affect the interactions between members of different trophic levels. Consequently, we review the progress that has been made in this exciting research field during the past 30 years since the first studies on HIPVs emerged and we highlight important issues to be addressed in the future.

The Role of Root-Produced Volatile Secondary Metabolites in Mediating Soil Interactions

“…Particularly, plant volatile organic compounds (VOCs), which mainly comprise terpenoids, fatty acid derivatives, phenyl propanoids and benzenoids (Dudareva, Pichersky, and Gershenzon 2004) have been the center of intensive studies of plant-herbivore-predator interaction for more than two decades (Dicke and Sabelis 1988;Turlings, Tumlinson, and Lewis 1990). VOCs blends can be complex, comprising hundreds of compounds, some of which are not produced by intact or mechanically damaged plants and others of which are synthesized de novo in response to herbivore attack (Mumm and Dicke 2010;Turlings and Wäckers 2004).…”

Parasitoid-specific induction of plant responses to parasitized herbivores affects colonization by subsequent herbivores

“…Such interactions between plants and carnivorous arthropods may ultimately increase fitness of the plants (1)(2)(3). Plant traits involved in such interactions include those that provide a predator/parasitoid with a resource such as, for example, food or shelter, or with information on the presence and abundance of herbivorous prey/hosts (4,5).…”

Manipulation of Natural Enemies in Agroecosystems: Habitat and Semiochemicals for Sustainable Insect Pest Control

“…Specifically, plants damaged by herbivores often produce a blend of volatiles (Paré & Tumlinson, 1999), commonly referred to as herbivore-induced plant volatiles (HIPVs) (Mumm & Dicke, 2010). These HIPVs consist of a mixture of the so-called green-leaf volatiles (C 6 aldehydes, alcohols, and acetates), terpenes (monoterpenes, sesquiterpenes, homoterpenes), and aromatic compounds, among others (Pichersky et al, 2006).…”

“…Ample evidence exists in the literature from laboratory studies that natural enemies can respond to HIPVs (Mumm & Dicke, 2010). For example, Anaphes iole Girault, an egg parasitoid of Lygus spp., showed a strong antennal response (based on electroantennogram -EAG-analysis) to (Z)-3-hexenyl acetate and MeSA (Williams et al, 2008).…”