Search

Plants synthesize variable mixtures of herbivore-induced plant volatiles (HIPVs) as part of their evolutionary conserved defense. To elucidate the impact of chewing herbivores with different level of adaptation on HIPV profiles in rice, we measured HIPVs released from rice seedlings challenged by either the generalist herbivore Mythimna loreyi (MYL) or the specialist Parnara guttata (PAG). Both herbivores markedly elicited the emission of HIPVs, mainly on the second and third days after attack compared to control plants. In addition, side-by-side HIPV comparisons using MYL and PAG caterpillars revealed that generalist feeding induced comparably more HIPVs relative to specialist, particularly on day two as highlighted by multivariate analysis (PLS-DA) of emitted HIPVs, and further confirmed in mimicked herbivory experiments. Here, mechanically wounded plants treated with water (WW) released more VOCs than untreated controls, and on top of this, oral secretions (OS) from both herbivores showed differential effects on volatile emissions from the wounded plants. Similar to actual herbivory, MYL OS promoted higher amounts of HIPVs relative to PAG OS, thus supporting disparate induction of rice indirect defenses in response to generalist and specialist herbivores, which could be due to the differential composition of their OS. (196 words).

Plant secondary metabolites play an important role in mediating interactions with insect herbivores and their natural enemies. Metabolites stored in plant tissues are usually investigated in relation to herbivore behaviour and performance (direct defence), whereas volatile metabolites are often studied in relation to natural enemy attraction (indirect defence). However, so-called direct and indirect defences may also affect the behaviour and performance of the herbivore's natural enemies and the natural enemy's prey or hosts, respectively. This suggests that the distinction between these defence strategies may not be as black and white as is often portrayed in the literature. The ecological costs associated with direct and indirect chemical defence are often poorly understood. Chemical defence traits are often studied in two-species interactions in highly simplified experiments. However, in nature, plants and insects are often engaged in mutualistic interactions with microbes that may also affect plant secondary chemistry. Moreover, plants are challenged by threats above- and belowground and herbivory may have consequences for plant-insect multitrophic interactions in the alternative compartment mediated by changes in plant secondary chemistry. These additional associations further increase the complexity of interaction networks. Consequently, the effect of a putative defence trait may be under- or overestimated when other interactions are not considered., (© 2014 John Wiley & Sons Ltd.)

Plants respond to herbivory with the emission of plant volatiles, which can be used by the herbivores' natural enemies to locate their hosts or prey. In nature, plants are often simultaneously confronted with insect herbivores and phytopathogens, potentially interfering with the attraction of the herbivores' enemies as a result of modifications of the induced volatile blend. Here, we investigated parasitoid (Cotesia glomerata) attraction to volatiles of plants challenged by different attackers, either alone or in combination with Pieris brassicae caterpillars, hosts of C. glomerata. We used a natural system consisting of Brassica nigra plants, eggs and larvae of P. brassicae, Brevicoryne brassicae aphids and the bacterial phytopathogen Xanthomonas campestris pv. campestris. In all cases, parasitoids successfully located host-infested plants, and wasp foraging behaviour was unaffected by the simultaneous presence of a non-host attacker or host eggs. Analysis of the volatile emissions show that the volatile blends of caterpillar-infested treatments were different from those without caterpillars. Furthermore, dually attacked plants could not be separated from those with only caterpillars, regardless of non-host identity, supporting the behavioural data. Our results suggest that, in this system, indirect plant defences may be more resistant to interference than is generally assumed, with volatiles induced during dual attack remaining reliable indicators of host presence for parasitoids., (© 2014 John Wiley & Sons Ltd.)

Avian species were historically thought to have a very limited sense of smell. However, recent studies suggest that odor plays an important role in many areas of avian life, including foraging and navigation. It has been shown that insectivorous birds can interact in a tritrophic fashion with plants and their herbivores by cuing in on herbivore-induced plant volatiles (HIPVs), important signaling compounds released by plants in response to herbivorous damage. This phenomenon has been observed in a number of plant species, including complex HIPV blends in corn (Zea mays). However, in other species, simpler single-compound HIPVs can act as phytohormones, causing the release of additional HIPVs, and have also been shown to be attractive to birds. Here we test if 2 single-compound general HIPVs, methyl jasmonate and methyl salicylate, attract avian predators to insect prey on corn plants using clay caterpillar models. We observed appreciable levels of bird attacks on our models across 10 experimental sites. However, we did not observe any difference between HIPV and control treatments. Interestingly, we did find that several weather variables, including wind speed and temperature, were significant or near significant predictors of avian predation activity, respectively. Together with previous studies, our results add to a nuanced picture of how birds may be using HIPVs to locate insect prey. Additionally, the potential for birds to act as a natural form of biocontrol in agricultural settings may be affected by physical location and local climate. On pensait historiquement que les espèces aviaires avaient une olfaction très limitée. Cependant, des études récentes suggèrent que l'odeur joue un rôle important dans de nombreux domaines de la vie aviaire, y compris la recherche de nourriture et la navigation. Les oiseaux insectivores peuvent interagir à travers trois niveaux trophiques avec les plantes et leurs herbivores par les signaux des substances volatiles végétales induites par les herbivores (HIPV), les composés de signalisation importants libérés par les plantes en réponse aux dommages causés par les herbivores. Ce phénomène a été observé chez plusieurs espèces végétales, comme le maïs (Zea mays) et ses mélanges complexes d'HIPV. Chez d'autres espèces, les HIPV plus simples et mono-composés peuvent agir comme des phytohormones, provoquant l'émission d'autres HIPV, qui se sont également avérés attrayants pour les oiseaux. Ici, nous testons si deux HIPV à un seul composé, le jasmonate de méthyle et le salicylate de méthyle, attirent les prédateurs aviaires vers les insectes proies sur les plants de maïs en utilisant des modèles de chenilles en argile. Nous observâmes des niveaux appréciables d'attaques d'oiseaux sur nos modèles dans dix sites expérimentaux. Cependant, nous ne trouvâmes aucune différence entre les traitements d'HIPV et les témoins. Il est intéressant de noter que nous constatâmes que plusieurs variables météorologiques, notamment la vitesse du vent et la température, étaient des prédicteurs significatifs ou presque significatifs de l'activité de prédation aviaire, respectivement. Nos résultats, combinés à des études précédentes, décrivent comment les oiseaux peuvent utiliser les HIPV pour localiser les proies d'insectes. De plus, le potentiel des oiseaux à agir comme une forme naturelle de lutte biologique dans les milieux agricoles peut être affecté par l'environnement physique et le climat local. [ABSTRACT FROM AUTHOR]