Published online March 14, 2022
Journal of Ecology and Environment (2022) 46:07
© The Ecological Society of Korea.
1Agricultural Science and Technology Institute, Andong National University, Andong 36729, Republic of Korea
2Department of Applied Chemistry, Adama Science and Technology University, Adama, P.O. Box 1888, Ethiopia
3Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea
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Background: Pollinators help plants to reproduce and support economically valuable food for humans and entire ecosystems. However, declines of pollinators along with population growth and increasing agricultural activities hamper this mutual interaction. Nectar and pollen are the major reward for pollinators and flower morphology and volatiles mediate the specialized plant?pollinator interactions. Limited information is available on the volatile profiles attractive to honey bees and bumblebees. In this study we analyzed the volatile organic compounds of the flowers of 9 different plant species that are predominantly visited by honey bees and bumblebees. The chemical compositions of the volatiles were determined using a head space gas chromatography-mass spectrometry (GC-MS) method, designed to understand the plant-pollinator chemical interaction. Results: Results showed the monoterpene 1,3,6-octatriene, 3,7-dimethyl-, (E) (E-β-ocimene) was the dominating compound in most flowers analyzed, e.g., in proportion of 60.3% in Lonicera japonica, 48.8% in Diospyros lotus, 38.4% Amorpha fruticosa and 23.7% in Robinia pseudoacacia. Ailanthus altissima exhibited other monoterpenes such as 3,7-dimethyl-1,6-octadien-3-ol (β-linalool) (39.1%) and (5E)-3,5-dimethylocta-1,5,7-trien-3-ol (hotrienol) (32.1%) as predominant compounds. Nitrogen containing volatile organic compounds (VOCs) were occurring principally in Corydalis speciosa; 1H-pyrrole, 2,3-dimethyl- (50.0%) and pyrimidine, 2-methyl- (40.2%), and in Diospyros kaki; 1-triazene, 3,3-dimethyl-1-phenyl (40.5%). Ligustrum obtusifolium flower scent contains isopropoxycarbamic acid, ethyl ester (21.1%) and n-octane (13.4%) as major compounds. In Castanea crenata the preeminent compound is 1-phenylethanone (acetophenone) (46.7%). Conclusions: Olfactory cues are important for pollinators to locate their floral resources. Based on our results we conclude monoterpenes might be used as major chemical mediators attractive to both honey bees and bumblebees to their host flowers. However, the mode of action of these chemicals and possible synergistic effects for olfaction need further investigation.
Keywords: pollinators, honey bees, bumblebees, flowers, monoterpenes, β-ocimene
Given the growing global human population, there is a need to assure food security (Khalifa et al. 2021). With this necessity, there have been many researches dealing with plant-pollinator interactions. However, consequences of plant-pollinator interactions are geographically variable (Hiraiwa and Ushimaru 2017; Johnson et al. 2017; Ollerton 2012; Ollerton 2017; Zanata et al. 2017), and this variation is still not well documented and difficult to elucidate owing to various factors associated with pollination (Ollerton 2012). While many gymnosperm plants depend on the wind and water for their pollination (Funamoto 2019; Khalifa et al. 2021), animal pollinators including insects, bats and birds have contributed to pollination and seed production of angiosperms. Most of flowering plants are not dependent on just one pollinator, but involve a broad spectrum of pollinators. Among which bees are the major and most important contributors for the production of several leading agricultural crops worldwide (Klein et al. 2007; Proctor and Yeo 1973). It is an accepted fact that bee-pollinated crops contribute approximately one-third of the total human dietary needs.
The reason bees are significant pollinators is due to their effectiveness and availability. Literature reports indicate that 87 global crops such as cocoa (
Exploring the causes of the declines of bees along with their host plants requires identifying signals that mediate their interactions. Foraging bees help moving pollen from one flower to the other and at the same time getting floral rewards such as pollen, nectar, oils, and resins. For getting rewards, bees use visual, olfactory, and tactile floral cues to locate their host plants (Dobson 2017; Giurfa et al. 1996; Kevan and Lane 1985; Lacher 1964; Menzel 1985; Vareschi 1971; Whitney et al. 2009). They are also capable of learning floral signals during their foraging periods (Beekman 2005; Kaiser and De Jong 1993; Menzel et al. 1974; Smith 1991; Zhang et al. 2006). In general bees depend mainly on olfactory and visual cues during their early foraging trips with visual cues becoming increasingly important in host-plant finding for experienced bees due to their learning capability (Dobson 2017).
Volatile organic compounds from host plants are known to influence the interaction, communication, and recruitment between active and inactive workers in the colony of honey bees, bumblebees, and stingless bees (Arenas et al. 2007; Arenas et al. 2008; Díaz et al. 2007; Dornhaus and Chittka 1999; Free 1969; Getz and Smith 1987; Jakobsen et al. 1995; Johnson 1967; Koltermann 1969; Lindauer and Kerr 1960; Molet et al. 2009; Reinhard et al. 2004a; Reinhard et al. 2004b; Ribbands 1954; Wenner et al. 1969). Each bee colony might forage on different flowers and thereby acquire different odours that result in the development of colony-specific patterns of floral odours (Smith and Breed 1995). For example pheromones that contain floral scents such as 1,8-cineole, (
The main aim of the current study was to identify volatile organic compounds scent bouquets, and to characterize which of these compounds might eventually be common or distinct in different flower scents of bee-pollinated plants. Our final goal is to analyze chemical compounds responsible for the attractiveness of these scents to the various bee species.
Bees hosting flowers were collected from the surroundings of Andong National University, Andong, Gyeongsangbuk-do (Republic of Korea), during spring and summer seasons in 2018. We collected 9 different plant species that are predominantly visited by honey bees and bumblebees in each flowering season (Table 1). The plant flowers were selected for this study based on our field observation of frequent visitation of honey bees and bumble to these flowers. Eight of these plants were trees and only
GC-MS analysis was done by using a GC (7890B; Agilent Technologies, Santa Clara, CA, USA) coupled with an MS (5977A Network; Agilent Technologies). The GC had an HP 5MS column (non-polar column, Agilent Technologies), 30 m × 250
Amount of volatile of organic compounds (VOCs) can potentially be affected by the flower species. Thus, the detected amounts of VOCs of each plant were transformed to compositional proportions to compare between plant species. To classify plant species by extracted VOCs, principal component analysis (PCA) was conducted with the “prcomp” function in R. 4.1.1 (R Core Team 2021). We used proportional values (> 1%) of VOCs from each species for analysis. A hierarchical cluster analysis (HCA) was also performed to evaluate similarity between proportional chemical compositions of sampled species. Ward’s variance minimizing method was applied for this analysis (Ward, 1963) and the result was visualized as a dendrogram. The analysis was conducted using the “hclust” function in R 4.1.1 (R Core Team 2021).
In this study we analyzed the chemical composition of the floral fragrances of nine flowers of different plant species belonging to 7 families. These plants were selected based on our field observation as host flowers of mainly honey bees and bumblebees. The VOC compositions of the floral scents are shown in Table 2. We identified 173 different VOCs from 9 plant species through the GC-MS analysis.
Out of a total 173 identified VOCs, 83 VOCs, which represents at least 1% in one species, were used for PCA and HCA. Biplot created by principal two components potentially represented that VOC proportion can differentiate flower of plant species (Fig. 1). In Figure 1, 1,3,6-octatriene, 3,7-dimethyl-, (
In order to compare the VOC profiles of 9 bee pollinated flowers and aggregate those with similar profiles, the hierarchical clustering method was applied as a dendrogram plot shown in Figure 2. A cut-off distance level indicated a distribution of the flowers in three homogeneous classes. The first cluster includes
Our results showed there are differences in the emission of floral volatile organic compounds among the nine bees host flowers investigated in this study. However, monoterpene,
Several reports indicate a role of
Dötterl and Vereecken (2010) reviewed floral scent eliciting positive behavioral responses in bee species such as
Major components in VOC of
Although not identified as ‘major’, some volatile organic compounds in the current study were reported to elicit positive behavioral responses in experienced bees or those for whom experience was not investigated (Dötterl and Vereecken 2010). These compounds include benzyl alcohol identified in the flower scent of
Floral emission of volatiles is a complex phenomenon that leads mixtures of organic compounds, having a high variable constituents and high relative amounts of compounds. Both these two aspects may play important roles in pollinators, especially insects’ attraction. It has been noted that some monoterpenes including
Additionally, apart from a species-specific response, relative percentages in blends may play a crucial role and even non-active compounds can enhance the attractiveness of other volatiles by lowering the active threshold dose of active ones (Chen and Song 2008).
Insects use both olfactory and visual cues to find flowers (Raguso and Willis 2002), offering pollinators decoupled cues or a combination of both cues. Some insects respond more to visual (Balkenius et al. 2006; Dötterl et al. 2011; Omura and Honda 2005; Roy and Raguso 1997) and others more to olfactory cues (Dötterl et al. 2011), but it would seem that in many species a combination of both cues is needed to elicit specific behavioral responses. The study results from the visual, olfactory and combined experiments on Salix caprea by (Dötterl et al. 2014) showed that visual and olfactory cues are also important for naive honey bees to find their host. Bees distinctively respond to decoupled olfactory and visual cues of the flower, but olfactory cues were more attractive than visual cues alone, but most honey bees were attracted to a combination of both cues rather than either of them alone.
Based on our results we conclude that monoterpenes might be used as major chemical mediators for honey bees and bumblebees in locating their host flowers. Among monoterpenes,
Supplementary information accompanies this paper at https://doi.org/10.1186/jee.21.001
Fig. S1. Chromatographic profiles of
We appreciate Prof. Victor Benno Meyer-Rochow for English correction and proof reading of the manuscript.
VOC: Volatile of Organic compounds
GC-MS: Gas chromatography-mass spectrometry
HP 5MS: HP-5 5% Diphenyl/95% Dimethylpolysiloxane
EI: Electron ionization
NIST: The National Institute of Standards and Technology
AD and CJ designed the study together. AD submitted the samples for analysis and analyzed the data and wrote the manuscript. MK and MS did the statistical analysis and wrote the manuscript. CJ reviewed and edited the manuscript. Both authors read and approved the final manuscript.
This work was partly supported by National Research Foundation of Korea (NRF-2018R1A6A1A03024862) and Rural Development Administration (RDA, PJ0157462021).
The datasets used and/or analyzed during the current study are available from the corresponding author (Prof. Chuleui Jung) on reasonable request.
The authors declare that they have no competing interests.