Abstract
Floral scents are important pollinator attractants, but there is limited knowledge about the importance of single components in plant–pollinator interactions. This especially is true in crop pollination systems. The aim of this study is to identify floral volatiles of several European pear cultivars (Pyrus communis L.), and to determine their potential in eliciting physiological responses in antennae of honey bees (Apis mellifera L.), the most important pollinators of pear. Volatiles were collected by dynamic headspace and analysed by (high resolution) gas chromatography coupled to mass spectrometry (GC/MS) and nuclear magnetic resonance spectroscopy. Antennal responses were investigated by GC coupled to electroantennographic detection (GC/EAD). We trapped in the mean 256 ng of scent per flower and hour (flower−1 h−1) from the different cultivars with either linalool + methyl benzoate or methyl 2-hydroxy-3-methylpentanoate as most abundant compounds. Of the 108 detected pear floral scent components, 17 were electrophysiologically active in honey bee antennae. Among these compounds were (E)-N-(2-methylbutyl)- and (E)-N-(3-methylbutyl)-1-(pyridin-3-yl)methanimine, which were not known from nature before to the best of our knowledge. Most other compounds identified as flower scent in pear are widespread compounds, known from flowers of various other species. Our results provide new insights in the floral volatile chemistry of an important insect-pollinated crop and show for the first time that honey bees have the olfactory ability to detect several pear floral volatiles. These data are an important basis for more detailed studies of the olfactory communication between honey bees and European pear flowers and might in the long term be used to manipulate the attractiveness of pear to obtain optimal fruit set.
Highlights
Pollinators are typically attracted to flowers by visual and olfactory cues (Bogdany and Taber 1979; De Jong and Pham-Delègue 1991; Dobson et al 1999; Burger et al 2010; Dötterl et al 2011), with the relative importance of the cues varying among pollination systems (Ômura and Honda 2005; Balkenius et al 2006; Dötterl et al 2011), there is limited knowledge about the detailed communication between flowers of fruit crops and their pollinators
We identified (i) compounds emitted by the flowers of ten pear cultivars using gas chromatography coupled to mass spectrometry (GC/MS), nuclear magnetic resonance (NMR), and chemical synthesis and (ii) analysed the antennal responses of honey bees (A. mellifera) to the emitted volatiles using GC coupled to electroantennographic detection (GC/EAD)
Six (AL (1 and 2), C, GräGfirnävfionnPvaorisn Paris (GP), KB, VDB, and WDB) of the nine cultivars emitted a quite similar spectrum of volatiles, with at least 92 compounds per cultivar (Fig. 2A; Table 1), whereas samples collected from trees of Köstliche von Charneux (KC), Clapps Liebling (CL) (1 and 2) and T contained less components (70–85)
Summary
Pollination by animals is one of the most important ecosystem services (Ollerton et al 2011), as wild plants and agricultural crops benefit from animal pollination (McGregor 1976; Free 1993; Williams 1994 in Klein et al 2007; Delaplane et al 2000; Khan and Khan 2004; KleinHandling Editor: Marko Rohlfs. pollinators are typically attracted to flowers by visual and olfactory cues (Bogdany and Taber 1979; De Jong and Pham-Delègue 1991; Dobson et al 1999; Burger et al 2010; Dötterl et al 2011), with the relative importance of the cues varying among pollination systems (Ômura and Honda 2005; Balkenius et al 2006; Dötterl et al 2011), there is limited knowledge about the detailed communication between flowers of fruit crops and their pollinators. A few fruit crops, it was just recently demonstrated that the main floral scent constituents are capable of attracting pollinators when offered as single synthetic compounds or synthetic mixtures (e.g., Cordeiro et al 2017; El-Sayed et al 2018; Krug et al 2018) Compounds involved in such interactions are, among others, a mixture of benzyl alcohol, 2-phenylethanol, hexanal, 1-hexanol, (Z)-3-hexen-1-ol, and 1-octanol in cambuci plants (Campomanesia phaea, Myrtaceae; Cordeiro et al 2017), 4-oxoisophorone and 3,5-dimethoxytoluene in Prunus species (apricot, P. armeniaca; European plum, P. domestica; peach, P. persica; all Rosaceae; El-Sayed et al 2018) and linalool and linalool oxides in guarana (Paullinia cupana, Sapindaceae; Krug et al 2018). The impact on pollination of dipteran and lepidopteran species, which visit pear flowers (Mc Gregor 1976 and references therein), was not yet investigated
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