Volatile production differs between oak leaves infested by leaf-miner Phyllonorycter harrisella (Lepidoptera: Gracillariidae) and galler Neuroterus quercusbaccarum (Hymenoptera: Cynipidae)

Fabian S Klimm,Alexander Weinhold,Martin Volf

doi:10.14411/eje.2020.011

Abstract

Plants defend themselves by producing various volatile organic compounds (VOCs) that have direct and indirect effects on insect herbivores. Their production is often specific to the plant and herbivore species involved, with some herbivores being able to manipulate their production. Here, we used passive volatile sampling using polydimethysiloxane (PDMS) tubing to compare VOCs produced by control, mined and galled oak leaves in the field. Leaves mined by a microlepidopteran leaf-miner (Phyllonorycter harrisella) produced a lower amount of two sesquiterpenes and an increased amount of eucalyptol. In contrast, leaves galled by the gall wasp (Neuroterus quercusbaccarum) did not produce a lower amount of any of the VOC measured when compared to the control. They produced a higher amount of farnesene, β-bourbonene and eucalyptol. Some of these VOC are known for their anti-herbivore function. In a second experiment, we treated the experimental leaves with the phytohormone methyl jasmonate (MeJA) to determine if leaf-miners or gallers reduced the overall inducibility of infested leaves. MeJA induced a sixteen-fold increase in VOC production. However, there was no difference in VOC production of control, mined and galled leaves treated with MeJA. Our results show that up- and down-regulation of VOCs can vary among leaves infested by different herbivores. More experiments are needed to determine if this is due to manipulation by the herbivores themselves or due to a defensive response of the plant.

Highlights

With approximately 6.1 million estimated species, arthropods are a highly successful group (Hamilton et al, 2013)
We treated the experimental leaves with the phytohormone methyl jasmonate (MeJA) to determine if leaf-miners or gallers reduced the overall inducibility of infested leaves
There was no difference in volatile organic compounds (VOCs) production of control, mined and galled leaves treated with MeJA

Summary

Introduction

With approximately 6.1 million estimated species, arthropods are a highly successful group (Hamilton et al, 2013). Their diversity is most commonly ascribed to the diversity of their feeding strategies, of which herbivory is the most widespread (Slansky & Rodriguez, 1987). Plants have developed various defensive strategies, including a huge variety of secondary metabolites with both direct and indirect effects on herbivores (Degen et al, 2004; Wink, 2006). Direct chemical defences are targeted directly at the herbivore, affecting its behaviour or physiology. Indirect chemical defences, such as herbivore induced plant volatiles (HIPVs), attract the predators and parasitoids of the herbivore (Aljbory & Chen, 2018). Blends of volatile organic compounds (VOCs) emitted by herbivoredamaged leaves stimulate parasitoid ovipositional probing behaviour (Dutton et al, 2000) or attract birds (Mäntylä et al, 2008; Amo et al, 2013)

Methods

Results

Conclusion