Herbivore-Induced Plant Volatiles Mediate In-Flight Host Discrimination by Parasitoids

Abstract

Abstract-Herbivore feeding induces plants to emit volatiles that are detectable and reliable cues for foraging parasitoids, which allows them to perform oriented host searching. We investigated whether these plant volatiles play a role in avoiding parasitoid competition by discriminating parasitized from unparasitized hosts in flight. In a wind tunnel set-up, we used mechanically damaged plants treated with regurgitant containing elicitors to simulate and standardize herbivore feeding. The solitary parasitoid Cotesia rubecula discriminated among volatile blends from Brussels sprouts plants treated with regurgitant of unparasitized Pieris rapae or P. brassicae caterpillars over blends emitted by plants treated with regurgitant of parasitized caterpillars. The gregarious Cotesia glomerata discriminated between volatiles induced by regurgitant from parasitized and unparasitized caterpillars of its major host species, P. brassicae. Gas chromatography-mass spectrometry analysis of headspace odors revealed that cabbage plants treated with regurgitant of parasitized P. brassicae caterpillars emitted lower amounts of volatiles than plants treated with unparasitized caterpillars. We demonstrate (1) that parasitoids can detect, in flight, whether their hosts contain competitors, and (2) that plants reduce the production of specific herbivoreinduced volatiles after a successful recruitment of their bodyguards. As the induced volatiles bear biosynthetic and ecological costs to plants, downregulation of their production has adaptive value. These findings add a new level of intricacy to plantYparasitoid interactions.

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

“…Regurgitant of parasitized caterpillars was collected from fourth-instar caterpillars that contained full-grown parasitoid larvae. To obtain enough regurgitant for each treatment, we used a capillary to collect regurgitant from several caterpillars, each regurgitating between 1 and 5 μL (14). There were clear differences in color among regurgitants collected from unparasitized caterpillars and caterpillars parasitized by different parasitoids (Fig.…”

“…When a parasitoid parasitizes an herbivore, the parasitoid larva affects performance of the herbivore that, as a result, interacts differently with the host plant (13,14). One effect that parasitoid larvae may have on herbivores is that, because of their feeding, they alter the physiology of the herbivore and, consequently, their oral secretions (13,14).…”

“…When a parasitoid parasitizes an herbivore, the parasitoid larva affects performance of the herbivore that, as a result, interacts differently with the host plant (13,14). One effect that parasitoid larvae may have on herbivores is that, because of their feeding, they alter the physiology of the herbivore and, consequently, their oral secretions (13,14). Compounds in the oral secretions or midgut regurgitant of caterpillars have been found to play a major role in the induction of herbivore-induced VOCs, which is mediated by the jasmonic acid (JA) signal-transduction pathway (15)(16)(17)(18)(19).…”

Precise Manipulation Through a Modeling Study

“…However, after herbivores have been eliminated, continuation of the emission is no longer needed for the plant, and if the emission continues, this is likely to devaluate the volatiles as a signal to carnivorous arthropods. In the research field of HIPV, more attention has been paid to the induction of volatiles (Scascighini et al 2005;Maffei et al 2007) than to the relaxation of their production and emission (Fatouros et al 2005). To investigate the effects of genetic variation in parasitoids, fewer tools are available at present.…”

Defesas induzidas por herbivoria e interações específicas no sistema tritrófico soja-percevejos-parasitoides de ovos

“…As DIH podem ter atuação direta, ao repelir herbívoros (De Moraes et al, 2001;Kessler & Baldwin, 2001), ou indireta, pela atração de inimigos naturais, como insetos, aves ou nematoides entomopatogênicos (Dudareva et al, 2006). As DIH podem variar qualitativa e quantitativamente de acordo com: a espécie do herbívoro que realiza a injúria na planta; a presença de diferentes espécies de herbívoros em uma mesma planta; o tipo de hábito alimentar (mastigador ou sugador) do inseto; o estágio fisiológico e a espécie da planta hospedeira (Dicke & Hilker, 2003;Fatouros et al, 2005;Moraes et al, 2005).…”