Exogenous Application of Methyl Jasmonate Increases Emissions of Volatile Organic Compounds in Pyrenean Oak Trees, Quercus pyrenaica

Abstract

The tri-trophic interactions between plants, insects, and insect predators and parasitoids are often mediated by chemical cues. The attraction to herbivore-induced Plant Volatiles (HIPVs) has been well documented for arthropod predators and parasitoids, and more recently for insectivorous birds. The attraction to plant volatiles induced by the exogenous application of methyl jasmonate (MeJA), a phytohormone typically produced in response to an attack of chewing herbivores, has provided controversial results both in arthropod and avian predators. In this study, we examined whether potential differences in the composition of bouquets of volatiles produced by herbivore-induced and MeJA-treated Pyrenean oak trees (Quercus pyrenaica) were related to differential avian attraction, as results from a previous study suggested. Results showed that the overall emission of volatiles produced by MeJA-treated and herbivore-induced trees did not differ, and were higher than emissions of Control trees, although MeJA treatment showed a more significant reaction and released several specific compounds in contrast to herbivore-induced trees. These slight yet significant differences in the volatile composition may explain why avian predators were not so attracted to MeJA-treated trees, as observed in a previous study in this plant-herbivore system. Unfortunately, the lack of avian visits to the experimental trees in the current study did not allow us to confirm this result and points out the need to perform more robust predator studies.

Avian predation of insects on corn (Zea mays): Effects of methyl jasmonate, methyl salicylate, and weather conditions

“…Alternatively, these compounds could have acted hormonally on the focal plants themselves, causing the release of additional HIPVs or other primed defenses (Heil and Silva Bueno 2007, Ramadan et al 2011, Hagiwara et al 2021, Yu et al 2022). Other studies have applied methyl jasmonate by direct spray instead of through dispenser vials (Mäntylä et al 2014, Mrazova and Sam 2018, Saavedra and Amo 2018b, Amo et al 2022), which may have elicited stronger internal signaling effects and the release of additional HIPVs. While our study did not differentiate between these 2 possibilities, we nevertheless still did not find any difference in methyl jasmonate or methyl salicylate treatments compared to controls.…”

“…Studies testing the attractive effects of methyl jasmonate or methyl jasmonate-induced HIPV release on insectivorous birds have yielded conflicting results across different plant species, with some studies finding no effect of methyl jasmonate treatment (Mäntylä et al 2014, Saavedra and Amo 2018b, Nguyen et al 2022), but others showing clearer avian recruitment effects (Mrazova and Sam 2018, Amo et al 2022). In contrast, a lower number of studies using methyl salicylate have shown clearer attractive effects (Rubene et al 2019, Nguyen et al 2022).…”

“…Both compounds are found in many plant species (Wasternack and Parthier 1997, Cheong and Choi 2003, Rodriguez-Saona et al 2011). However, the capacity for insectivorous birds to cue in on methyl jasmonate induced HIPVs to find insect prey is unclear (Mäntylä et al 2014, Mrazova and Sam 2018, Saavedra and Amo 2018b, Mrazova et al 2019, Amo et al 2022, Nguyen et al 2022). While methyl salicylate has been less studied, it has shown a more promising attractive effect on recruiting avian predators (Rubene et al 2019, Nguyen et al 2022).…”