Volatiles Induced from Hypolepis punctata (Dennstaedtiaceae) by Herbivores Attract Sclomina erinacea (Hemiptera: Reduviidae): Clear Evidence of Indirect Defense in Fern.

Kerui Huang,Hui Shen,Qiong Zhou,Hui Shang,Yuehong Yan,Yun Wang

doi:10.3390/insects12110978

Abstract

Simple SummaryPlants have developed many kinds of indirect defense mechanisms against herbivorous insects, through which the natural enemies are attracted by herbivore-induced plant volatiles to prey on these phytophagous species. There have been many reports regarding this mechanism in spermatophytes, but little is known in ferns. In this study, the relationship between the fern species Hypolepis punctata and the predatory insect Sclomina erinacea was studied. Employing field observations, plant volatile analysis, electrophysiological experiments, and behavioral experiments, we found that not only the plant can attract the assassin bug in the field, but compared with the healthy individuals, the fern being damaged by herbivorous insects also emitted several novel volatile organic compounds, which were strongly attractive to the assassin bug. The results indicate that ferns may also have indirect defense mechanisms using volatile organic compounds, and it is the first report of an indirect defense mechanism in fern.Plants have evolved various self-defense mechanisms against insect feeding. There are many reports regarding both direct and indirect defense mechanisms in seed-plant. However, only direct defenses on ferns were considered and the indirect defense mechanism has never been reported. In this study, it was observed that the fern Hypolepis punctata can attract the assassin bug Sclomina erinacea in the field. We collected and analyzed volatiles from H. punctata healthy individuals and the ones wounded by Bertula hadenalis, using dynamic headspace and GC-MS. We recorded the electroantennogram responses of antennae of S. erinacea to different standards of volatile compounds identified from the GC-MS analysis. We also analyzed the behavior of male and female S. erinacea adults in response to volatiles collected from H. punctata using a Y-tube olfactometer. The results showed that a number of volatile compounds were produced when the fern was damaged by B. hadenalis. Electroantennography and Y-tube olfactometer results showed that some herbivore-induced volatiles and volatiles from undamaged leaves could attract S. erinacea. Our research suggests that H. punctata can attract insect predators by releasing herbivory-induced volatile organic compounds, and for the first time we found ferns may also have indirect defense mechanisms using volatile organic compounds.

Highlights

The relationship between plants and insects on earth is intricate
The S. erinacea usually stays on H. punctata for hours to a whole day during one visitation, the number of S. erinacea on each H. punctata individual was recorded in the morning
The visitation preference difference of S. erinacea individuals between the healthy and the damaged H. punctata in the field observation is shown in Table 2, which demonstrate that, during the seven days of field observations, S. erinacea individuals had a strong preference for the damaged Hypolepis punctata (p < 0.05) by herbivory for five days in the total seven days, indicating that the herbivory of phytophagous insects on H. punctata can affect the behavior of the assassin bug S. erinacea

Summary

Introduction

The relationship between plants and insects on earth is intricate. Among the approximately one million known insect species, 45% or more are herbivorous [1,2]. To reduce damage from insects, plants have evolved a series of direct or indirect defense mechanisms to prevent insects’ predation [3,4]. Plants have thorns on the surface and highly lignified tissues, and chemically, they produce various toxic or repellent metabolites against herbivorous insects [5]. The indirect defense is mainly achieved by attracting beneficial insects (such as predators) from additional trophic levels [6]. Being the most common attractant to these predators, volatile organic compounds (VOCs) secreted by plants are mainly terpenes, fatty acid derivatives, and some other aromatic compounds [7,8,9], they can function in the defense process of a single individual, but some can act as “alarms” to inform other plants to start defense [10,11,12]

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