Exploiting scents of distress: the prospect of manipulating herbivore-induced plant odours to enhance the control of agricultural pests

Abstract

In response to feeding by arthropods, plants actively and systemically emit various volatile substances. It has been proposed that these herbivore-induced volatiles (HIPVs) can be exploited in agricultural pest control because they might repel herbivores and because they serve as attractants for the enemies of the herbivores. Indeed, recent studies with transgenic plants confirm that odour emissions can be manipulated in order to enhance the plants' attractiveness to beneficial arthropods. An additional advantage of manipulating HIPV emissions could be their effects on neighbouring plants, as a rapidly increasing number of studies show that exposure to HIPVs primes plants for augmented defence expression. Targeting the right volatiles for enhanced emission should lead to ecologically and economically sound ways of combating important pests. IntroductionPlant defences against herbivores are not limited to physical and chemical barriers that directly aim to harm their attackers, it is becoming increasingly evident that plants also employ strategies of indirect defence. One form of indirect defence in plants is to attract predators and parasitoids by signalling the presence of potential prey or hosts. This attraction of the third trophic level is one of the presumed functions of herbivore-induced plant volatiles (HIPVs), which are released more or less specifically in response to herbivore attack. The first evidence for tritrophic signalling [1,2] has generated a remarkable interest in this phenomenon from scientists from a broad range of disciplines. This interest has resulted in what can be considered the most interdisciplinary approach to any aspect of plant-arthropod interactions. A rapidly increasing number of behavioural, chemical and evolutionary ecologists, plant physiologists and crop scientists devote their research efforts to the understanding of the mechanisms, selective pressures and ecological consequences of the interactions. Moreover, there is increased interest in understanding the implications of induced plant signalling in the light of agricultural pest control, as has been outlined in previous reviews [3][4][5]. Here we focus, after a brief historical account, on the latest developments in this area. In addition, we address the recent studies that point to a priming effect in plants that are exposed to certain HIPVs, conferring an enhanced defensive capacity against future insect attack [6 ,7-11]. We conclude, with some reservations, that there is not only reason for optimism that manipulation of HIPVs emissions can indeed lead to enhanced repulsion of pests and attraction of their natural enemies but, moreover, that enhanced volatile information transfer between plants might, if exploited appropriately, improve the efficiency of the plant's direct and indirect defence strategies through priming [4,12]. Figures 1 and 2 summarize the various interactions in which HIPVs are implicated as we have studied them for maize plants. The role of HIPVs in indirect plant defencesPrice and colleagues [13] w...

Apion miniatum Germ. Herbivory on the Mossy Sorrel, Rumex confertus Willd.: Induced Plant Volatiles and Weevil Orientation Responses

“…It is well known that manipulation of volatile emission in plants has enormous potential in relationship to pest management in agricultural contexts [43]. Manipulating these signals may help increase the effectiveness of attracting parasitoid and predatory natural enemies with induced VOCs to more effectively serve as biological control agents in agroecosystems.…”

The Role of Indole and Other Shikimic Acid Derived Maize Volatiles in the Attraction of Two Parasitic Wasps

“…Hence, this study suggests that parasitoids do not use all herbivore-induced VOCs for habitat and host location to a similar degree, but rather pay selective attention to a few compounds. Identifying these key compounds seems crucial for a good understanding of the host searching process in parasitoids and for the development of strategies to increase the efficiency of natural enemies for the control of pest insects (Turlings and Ton, 2006).…”

Is quality more important than quantity? Insect behavioural responses to changes in a volatile blend after stemborer oviposition on an African grass

“…Typically, insect attack leads to an increase in emission of plant volatile compounds that appear to function as a 'cry for help' to attract natural enemies in tritrophic interactions (Takabayashi & Dicke 1996;de Moraes et al 1998;Du et al 1998;Turlings & Ton 2006;Heil 2008) and repel further colonization by the herbivore itself (de Moraes et al 2001;Kessler & Baldwin 2001). Recently, it has been observed that plants increase volatile emission even at the earliest stage of herbivore attack, namely oviposition (Colazza et al 2004;Hilker & Meiners 2006).…”