- Importance of floral scent compounds for the interaction between Silene latifolia (Caryophyllaceae) and the nursery pollinator Hadena bicruris (Lepidoptera: Noctuidae) (2004)
- In the present study, the role of floral volatiles for the interaction between the nocturnal Caryophyllaceae Silene latifolia, and the noctuid moth Hadena bicruris was determined. This insect-plant relationship is one of the known nursery pollination systems, where pollinators reproduce within the flowers they pollinate. Silene latifolia is a dioecious weed, native to Europe and formerly introduced to North America. It is the main larval host plant of H. bicruris, which is distributed in Europe and North Africa. Especially night-active moths, among them H. bicruris, which are attracted by the flower scent, pollinate S. latifolia. However, until now, nothing was known about the role of single flower scent compounds for the attraction of the moths. This thesis describes the chemical composition and the geographical variability in the flower scent of S. latifolia. Furthermore, electrophysiological and behavioural tests with floral scent extracts and single authentic standard compounds were carried out in H. bicruris to identify the attractive compounds of the complex floral scent. To get an insight into the role of floral scent in guiding potential pollinators on flowers, the spatial fragrance pattern within the flowers of S. latifolia was determined, additionally. The variability in floral scent was very high, especially between different populations, and different chemotypes were characterised.Typical compounds in floral scent of S. latifolia were lilac aldehyde isomers, trans-beta-ocimene, benzaldehyde, phenyl acetaldehyde, or veratrole. Some of these compounds are known to attract nocturnal Lepidoptera species. To characterise antennal and behavioural responses of H. bicruris to various floral scent chemotypes of S. latifolia, and to S. vulgaris (which is rarely also used as host plant), different S. latifolia extracts, and a S. vulgaris extract were analysed using GC-MS methods. These extracts were further used in GC-FID/EAG and GC-MS/EAG detections, respectively. Main compounds in the tested extracts often elicited main signals in the antennae (e.g. lilac aldehydes, phenyl acetaldehyde). Some compounds elicited main signals in the antennae, though they were only minor components in the extracts (e.g. 3-methyl-butyl-aldoxime, benzaldehyde). Other compounds elicited only weak signals in the antennae, though they were abundant in the extracts (e.g. myrcene, methyl benzoate). The compounds of the most common chemotypes of S. latifolia were very sensitively detected by Hadena bicruris, whereas compounds of less abundant chemotypes were less sensitively detected. Floral scent blends that were dominated by lilac aldehydes or phenyl acetaldehyde effectively attracted moths. Hadena bicruris can electrophysiologically and behaviourally distinguish between its main host plant, S. latifolia, and the similarly scented S. vulgaris, another rarely used larval host plant, only by their floral scent. To identify floral scent compounds of S. latifolia that are important for the attraction of H. bicruris, the GC-FID/EAD or the GC-MS/EAD method was used in a first step to identify compounds that elicit signals in the antennae of the moth. Electrophysiologically very active compounds were tested in wind tunnel bioassays, and the attractivity of these compounds was compared to the attractivity of the natural scent of whole flowers of S. latifolia. The antennae of H. bicruris detected substances of several compound classes such as monoterpenoids, benzenoids, fatty acid derivatives, and nitrogen-bearing compounds. Lilac aldehydes were the most attractive compounds in wind tunnel bioassays, and attracted 90% of the tested moths, as did the scent of single flowers. Some compounds did not attract any moth, though they elicited significant signals in the antennae. To determine the parts of the female and male flowers responsible for scent emission, volatiles from attached intact flowers were sampled and then single flower parts were progressively removed. After each preparation step, volatiles were collected from the remaining “flower”. Especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia; and compounds emitted from the petals differed from the compounds emitted by the anthophore. The anthophore emitted only lilac aldehydes and alcohols. Lilac aldehydes are known to be behaviourally very attractive for noctuid Lepidoptera such as Autographa gamma and Hadena bicruris, and they may serve as nectar guides in S. latifolia.