Multiple functions of volatiles in flowers and leaves of Elsholtzia rugulosa (Lamiaceae) from southwestern China.

Feng-Ping Zhang,Shi-Bao Zhang,Gang Wang,Qiu-Yun Yang

doi:10.1038/srep27616

Abstract

Although the roles of volatile compounds have been examined separately in plant–herbivore or plant–pollinator interactions, few studies have focused on how plant scents can attract effective pollinators, repel ineffective pollinators, and defend against attacks by insect herbivores. We explored the functional significance of volatile compounds that impart a strong odor to Elsholtzia rugulosa, a shrub species in southwestern China. We monitored the pollinating honey bee Apis cerana, as well as two occasional visitors – Vespa velutina and a Bombus sp. – and an herbivorous beetle Oxycetonia jocunda. Behavior experiments using Y-tubes showed that honey bees were attracted primarily by floral scent while hornets and bumble bees were repelled by both the flowers and leaves. Analysis via gas chromatography-mass spectrometry revealed that these tissue types differed in their compositions and relative amounts of volatile compounds. When the plants were damaged, the average relative amounts of Elsholtzia ketone rapidly increased in the flowers and leaves. Furthermore, herbivorous beetles were strongly repelled by damaged tissues, suggesting a potential defense signaling function by these compounds. Our findings again demonstrate that scents have multiple functions in the interactions among plants and insects.

Highlights

Observations have shown that hornets (Vespa velutina) and bumble bees (Bombus sp.) are occasional floral visitors to these flowers
We addressed the following: 1) do levels of these volatile compounds differ between flowers and leaves, 2) are some specific pollinators attracted by the scent of flowers and/or leaves, 3) can this strong odor deter ineffective pollinators, and 4) do the volatiles emitted by damaged tissues act as part of a defense mechanism against insect herbivores?
The fitness of flowering plants with specialized floral traits for pollinator attraction can decline if those flowers are visited by animals that are ineffective pollinators[23]

Summary

Introduction

Observations have shown that hornets (Vespa velutina) and bumble bees (Bombus sp.) are occasional floral visitors to these flowers (unpublished data). We visually confirmed that their heads and bodies did not make effective contact with the anthers and stigmas during visiting flowers occasionally, the longer tongues of hornets and bumble bees were unsuitable for pollination of E. rugulosa. The few hornets and bumblebees caught in the mist net were lacking E. rugulosa pollen. No reports have been made on either the constitution of the unusual sharp odor in leaves and flowers of E. rugulosa or the significance of its function. Whole-plant studies have examined the chemical components of its essential oils[22]. We addressed the following: 1) do levels of these volatile compounds differ between flowers and leaves, 2) are some specific pollinators attracted by the scent of flowers and/or leaves, 3) can this strong odor deter ineffective pollinators, and 4) do the volatiles emitted by damaged tissues act as part of a defense mechanism against insect herbivores?

Methods

Results

Conclusion