Flower volatiles, crop varieties and bee responses.

Pollination contributes to an estimated one third of global food production, through both the improvement of the yield and the quality of crops. Volatile compounds emitted by crop flowers mediate plant-pollinator interactions, but differences between crop varieties are still little explored. We investigated whether the visitation of crop flowers is determined by variety-specific flower volatiles using strawberry varieties (Fragaria x ananassa Duchesne) and how this affects the pollination services of the wild bee Osmia bicornis L. Flower volatile compounds of three strawberry varieties were measured via headspace collection. Gas chromatography showed that the three strawberry varieties produced the same volatile compounds but with quantitative differences of the total amount of volatiles and between distinct compounds. Electroantennographic recordings showed that inexperienced females of Osmia bicornis had higher antennal responses to all volatile compounds than to controls of air and paraffin oil, however responses differed between compounds. The variety Sonata was found to emit a total higher level of volatiles and also higher levels of most of the compounds that evoked antennal responses compared with the other varieties Honeoye and Darselect. Sonata also received more flower visits from Osmia bicornis females under field conditions, compared with Honeoye. Our results suggest that differences in the emission of flower volatile compounds among strawberry varieties mediate their attractiveness to females of Osmia bicornis. Since quality and quantity of marketable fruits depend on optimal pollination, a better understanding of the role of flower volatiles in crop production is required and should be considered more closely in crop-variety breeding

Identified flower volatile compounds of three strawberry varieties (ng g⁻¹ flowers). Ester, irregular terpenes and sesquiterpenes.

<p>Trace indicates average amount less than 0.1 ng g⁻¹ flowers. Bold font indicates significant <i>p-</i>values for the calculated model (glm). Different lower-case letters indicate significant pairwise differences between respective means of different strawberry varieties at p<0.05 (Tukey test). *: Stereochemistry not determined. Linear retention indices (LRI) were calculated from chromatograms obtained with a HP-5MS (LRI^a) and an HP-INNOWax (LRI^b) column. Identification (ID) is based upon mass spectrum matched with those of databases (Wiley 09, Nist 08, and Hochmuth, 2004). LRI is confirmed by synthetic standards. Source of synthetic standards: ¹ Fluka (Germany), ² Merck-Suchardt (Hohenbrunn, Germany), ³ Aldrich (Germany), ⁴ Acros (Germany), ⁵ Sigma-Aldrich (Steinheim, Germany), ⁶ TCI (Zwijndrecht, Belgium). n. d. = non detectable.</p

Antennal responses of naïve <i>O.</i><i>bicornis</i> females to synthetic compounds.

<p>Compounds were identified from flower volatile extracts of strawberry varieties (10⁻³ dilution; mean±SE, n = 10). p<0.05 = significant.</p

Abundance of <i>O.</i><i>bicornis</i> females between strawberry varieties.

<p>Data show mean numbers (±SE) of observed specimen per subunit. p<0.05 = significant.</p

Difference between varieties due to the emission of floral volatile compounds.

<p>Differences between varieties are shown as euclidian distance.</p