Floral scent composition in early diverging taxa of Asclepiadoideae,and Secamonoideae (Apocynaceae)

The Apocynaceae–Asclepiadoideae are well known for their specialized floral morphologies and pollination systems and many species have distinct floral aromas. However, our knowledge on the chemistry of floral volatiles in this plant family is relatively limited although it has been suspected that floral scent plays a key function for pollinator attraction. This is the third paper in a series of papers reporting on the floral odours of Asclepiadoideae. Floral odours of eleven species from seven genera (Cibirhiza, Fockea, Gymnema, Hoya, Marsdenia, Stephanotis and Telosma) of early diverging taxa of Apocynaceae–Asclepiadoideae, and two species of Secamone (Apocynaceae–Secamonoideae) were collected using headspace sampling and then analyzed via GC–MS. We detected 151 compounds, of which 103 were identified. The vast majority of chemicals identified are common components in flower odour bouquets of angiosperms. However, striking was the high relative amount of acetoin (97.6%) in the flower scent of Cibirhiza albersiana. This compound has rarely been reported as a flower scent component and is more commonly found in fermentation odours. Bray–Curtis similarities and Nonmetric-Multidiminsional Scaling (NMDS) analyses showed that each of the species has a distinct odour pattern. This is mostly due to only twelve compounds which singly or in different combinations dominated the scent of the species: the benzenoids benzyl acetate, benzaldehyde, methyl benzoate, and 2-phenylethyl alcohol; the monoterpenoids (E)-ocimene, (Z)-ocimene, linalool, and eucalyptol; and the aliphatic compounds acetoin, and (E,Z)-2,6-nonadienal. The floral scent compositions are discussed in relation to tribal affiliations and their potential role for pollinator attraction, and are compared with the scent data available from other Asclepiadoideae species.     

Floral scents produced by Lilium and Cardiocrinum species native to China

Floral scents of thirteen Lilium and one Cardiocrinum species native to China were collected by headspace adsorption during day and night periods and analyzed by gas chromatography and mass spectrometry. There was a positive correlation between volatile emissions and scent intensities. The scented and light-scented Lilium species emitted greater amounts of volatiles at night, and their predominant volatiles were monoterpenoids and benzenoids or monoterpenoids alone. The scent profiles provided useful taxonomic information in section Leucolirion. The major scent compounds of L. regale, L. sulphureum and L. sargentiae were 1,8-cineole (rarely linalool) and methyl benzoate. The closely related Cardiocrinum cathayanum was differentiated from scented Lilium species based on its high emission of (E,E)-α-farnesene and methyl salicylate. L. bakerianum var. delavayi and L. primulinum var. ochraceum emitted the key compound linalool only at night as well as trace quantities of methyl benzoate. Two chemotypes of floral scent were found in L. sargentiae and L. bakerianum var. delavayi, and their differences in volatile compositions were related to the monoterpenoids and benzenoids emissions, respectively. This work provides a basis for advanced studies on the reproductive biology of Lilium species.     

Spatial and temporal patterns of floral scent emission in Dianthus inoxianus and electroantennographic responses of its hawkmoth pollinator

Scent emission is important in nocturnal pollination systems, and plant species pollinated by nocturnal insects often present characteristic odor compositions and temporal patterns of emission. We investigated the temporal (day/night; flower lifetime) and spatial (different flower parts, nectar) pattern of flower scent emission in nocturnally pollinated Dianthusinoxianus, and determined which compounds elicit physiological responses on the antennae of the sphingid pollinator Hyles livornica.The scent of D.inoxianus comprises 68 volatile compounds, but is dominated by aliphatic 2-ketones and sesquiterpenoids, which altogether make up 82% of collected volatiles. Several major and minor compounds elicit electrophysiological responses in the antennae of H. livornica. Total odor emission does not vary along day and night hours, and neither does along the life of the flower. However, the proportion of compounds eliciting physiological responses varies between day and night. All flower parts as well as nectar release volatiles. The scent of isolated flower parts is dominated by fatty acid derivatives, whereas nectar is dominated by benzenoids. Dissection (= damage) of flowers induced a ca. 20-fold increase in the rate of emission of EAD-active volatiles, especially aliphatic 2-ketones.We suggest that aliphatic 2-ketones might contribute to pollinator attraction in D. inoxianus, even though they have been attributed an insect repellent function in other plant species. We also hypothesize that the benzenoids in nectar may act as an honest signal (‘nectar guide’) for pollinators.     

Floral scents of chafer-pollinated asclepiads and a potential hybrid

Floral scent is a key functional trait for pollinator attraction to flowers, but is poorly documented in many plant lineages and pollination systems. In South African grasslands, chafer beetles (Scarabaeidae: Cetoniinae), particularly Atrichelaphinis tigrina, Cyrtothyrea marginalis and Leucoscelis spp., are common floral visitors and specialized pollination by these beetles has recently been established in several asclepiad, orchid and protea species. Chafer beetles are known to be attracted by a variety of floral volatile compounds and scent has been suggested to be an important signal in these chafer-operated pollination systems. In this study, we used dynamic headspace extraction methods and coupled gas chromatography–mass spectrometry (GC–MS) to examine the chemical composition of the floral scents of seven putatively chafer-pollinated asclepiad species in the genera Asclepias, Pachycarpus and Xysmalobium. We identified 15–57 compounds in the scents of these species, of which seven were common to all species examined. The scent profiles of each species separate into discrete clusters in two dimensional space based on non-metric multidimensional scaling (NMDS), indicating clear distinctions between species and suggesting that plants may use different combinations of volatiles to attract beetles. Two plants suspected to be intergeneric hybrids were also examined. Data on pollination systems, morphology and scent chemistry are consistent with the hypothesis that these plants are hybrids between the chafer-pollinated species Asclepias woodii and Pachycarpus concolor. The results of this study are discussed in relation to the role of chafer beetles as generalist pollinators of specialized asclepiads.     

Variation in scent emission among floral parts and inflorescence developmental stages in beetle-pollinated Protea species (Proteaceae)

Floral fragrances are an important component for pollinator attraction in beetle-pollinated flowers. Several genera in the Proteaceae contain beetle-pollinated species. However, there is no information on the floral scent chemistry of beetle-pollinated members of the family. In this paper we report on the spatial variation and differences between developmental stages in emission of inflorescence (flowerhead) volatiles of four South African Protea species (P. caffra, P. dracomontana, P. simplex, and P. welwitschii) that are pollinated by cetoniine beetles. The scents from different inflorescence parts (bracts, perianth, styles, and nectar) and from successive anthesis stages of whole inflorescences were sampled using dynamic headspace collection and identified using GC–MS. Although the four species shared many scent compounds, possibly reflecting their close phylogenetic relationships and common pollinators, they showed significant differences in overall scent composition due to various species-specific compounds, such as the unique tiglate esters found in the scent of P. welwitschii. The strongest emissions and largest number of volatiles, especially monoterpenes, were from inflorescences at full pollen dehiscence. Senescing inflorescences of two species and nectars of all species emitted proportionally high amounts of acetoin (3-hydroxy-2-butanone) and aromatic alcohols, typical fermentation products. As a consequence, the scent composition of nectar was much more similar among species than was the scent composition of other parts of the inflorescence. These results illustrate how the blends of compounds that make up the overall floral scent are a dynamic consequence of emissions from various plant parts.     

Smells like debauchery: The chemical composition of semen-like,sweat-like and faintly foetid floral odours in Xysmalobium (Apocynaceae: Asclepiadoideae)

Floral volatiles play an important role in plant communication with both pollinators and antagonists, but remain poorly explored for many plant groups. Asclepiads (Apocynaceae: Asclepiadoideae subtribe Asclepiadinae) represent a diverse group in South African grasslands, but the scents of most species remain unexplored and few genera are sufficiently sampled to allow comparisons between congeners. I used dynamic headspace extraction methods and coupled gas chromatography-mass spectrometry (GC–MS) to examine the scent chemistry of three unusually scented asclepiads in the genus Xysmalobium and then combined these data with previously published data to explore inter- and intraspecific variation in the genus. A total of 74 compounds (33–44 per species) from various compound classes were detected in the species examined here. The sweet but faintly foetid scent of Xysmalobium asperum was dominated by epoxy oxoisophorone in combination with various other terpenoids and aromatics, and small amounts of p-cresol. The sweat-like scent of Xysmalobium tysonianum was dominated by a few aromatics in combination with isovaleric acid and several aliphatic compounds normally associated with microbial degradation or fermentation. The semen-like scent of Xysmalobium parviflorum flowers examined here contained large relative amounts of 1-pyrroline, and comparison with previously published data for dung-scented flowers from a different population revealed clear divergence in the relative amounts of this compound and p-cresol. I also detected 25 compounds that were not shared between the two X. parviflorum populations. Comparison of scent data for eight Xysmalobium species revealed very distinct chemical profiles with limited overlap between species. These results are discussed in relation to the possible roles of these volatiles as pollinator attractants and the evolution of floral scents within the genus.     

Flower scent composition in diurnal Silene species (Caryophyllaceae): phylogenetic constraints or adaption to flower visitors?

A comparative analysis of the flower volatiles of 10 day-flowering Silene species native to Central Europe was made to improve the understanding of the pollination biology and evolution of floral odours in the genus. Floral scent was collected by dynamic headspace adsorption and analysed via gas chromatography–mass spectrometry. In total, 60 compounds could be identified by their mass spectra as well as by their relative retention times. The number of compounds per species ranged between 16 in Silene rupestris and 40 in S. viscaria. Main compounds in most species were fatty acid derivatives (FADs, cis-3-hexen-1-ol, cis-3-hexenyl acetate, n-nonanal), benzenoids (benzaldehyde, phenylacetaldehyde, methyl benzoate), and monoterpenes (limonene, linalool), accompanied by sesquiterpenes, and nitrogen-containing compounds.Nonmetric multidimensional scaling (CNESS, NMDS) based on relative amounts of single components leads to the same conclusion as visualization of similarities based on component classes reflecting to some degree biosynthetic pathways: differences in floral scent composition can be related to both the taxonomy and the pollination biology of the species investigated. In all but one species of the Silene group, and all species of the Lychnis group (S. dioica, S. flos-cuculi, S. flos-jovis, S. pendula), the dominating compound classes are benzenoids followed by FADs. The relatively high amounts of aromatic compounds (e.g. benzaldehyde, phenylacetaldehyde, methyl benzoate) are indicative of an adaptation towards butterfly pollination. Species of the Viscaria and Eudianthe groups showed high relative amounts of FADs but a lower content of benzenoids. Relatively high amounts of monoterpenes (>10%) were found in S. alpestris, S. coeli-rosa, S. gallica, and S. viscaria. It is suggested that the high relative content of the most volatile monoterpene alkenes (e.g. limonene) in S. gallica and S. coeli-rosa may be indicative of an adaptation to bees as pollinators in these species.     

Flower scent composition in Dianthus and Saponaria species (Caryophyllaceae) and its relevance for pollination biology and taxonomy

Floral fragrance compounds of seven Dianthus species (D. arenarius, D. armeria, D. barbatus, D. deltoides, D. monspessulanus, D. superbus, and D. sylvestris) and one Saponaria species (S. officinalis) (Caryophyllaceae) were studied using headspace adsorption technique followed by gas chromatography massspectrometry (GC-MS). The number of compounds (fatty acid derivatives, benzenoids, phenyl propanoids, isoprenoids, and nitrogen containing compounds) identified in the floral odors ranged from 18 to 51 but all were dominated by only 1–3 compounds. Most of the compounds identified in this study have been previously reported in floral scents from species of the closely related genus Silene L. However, the phenyl propanoids eugenol, methyleugenol, methylisoeugenol, cis-asarone, and trans-asarone have formerly not been found in Silene. Based on the measurement of Sørensen’s index of similarity (I_s) nonmetric multidimensional scaling (MDS) was used to detect meaningful underlying dimensions and to visualize similarities between the investigated species. The MDS analysis showed three groups of species, (1) the diurnal D. armeria, D. barbatus, and D. deltoides are characterized by the predominance of fatty acid derivatives, (2) the closely related nocturnal D. monspessulanus, and D. superbus by high relative amounts of isoprenoids such as cis-β-ocimene and β-caryophyllene, and (3) the species D. arenarius, D. sylvestris and S. officinalis by a predominance of benzenoids, especially methylbenzoate. The results are discussed in relation to pollination, especially by butterflies, moths, and hawkmoths.     

Chemical composition of leaf volatiles in Macaranga species (Euphorbiaceae) and their potential role as olfactory cues in host-localization of foundress queens of specific ant partners

Host-plant finding by foundress queens is an important step in the establishment of ant–plant symbioses and olfactory cues may play a crucial role in the Macaranga–Crematogaster ant–plant system for attracting foundresses over longer distances. MicroSPE was used to investigate leaf volatiles of 11 myrmecophytic and non-myrmecophytic Macaranga species. Chemical analysis (GC–MS) yielded a total of 114 compounds comprising a great diversity, including aliphatic compounds, aromatics, mono- and sesquiterpenoids. An analysis of the volatile data using the CNESS distances of the chemical profiles, followed by visualization of the data with non-metric multidimensional scaling (NMDS) showed that even closely related species sharing the same ant partners have clearly different scent patterns. Comparison of spectra of volatile compounds between obligate myrmecophytic Macaranga species and myrmecophilous species that are only facultatively associated with unspecific arboreal ants did not reveal general differences. Choice experiments conducted with foundresses revealed that the ants have the capacity to distinguish between different host species. However, the behavior of the foundresses following surface contact with saplings indicates that other cues, like surface structure, may play a more important role in host-recognition over short distances than volatile compounds. We discuss alternative hypotheses for the possible role of leaf volatiles in the examined Macaranga species as chemical defense against herbivores.     

Spatial fragrance patterns in flowers of Silene latifolia: Lilac compounds as olfactory nectar guides?

Floral odour can differ qualitatively and quantitatively between different parts of the flowers, and these spatial fragrance patterns within the flowers can be used by pollinators for orientation on flowers. Here we present results of spatial fragrance patterns within flowers of the dioecious Silene latifolia (Caryophyllaceae). Volatiles were collected and analysed using a highly sensitive dynamic headspace method, which allows dramatically reducing the sample time. From all flower parts, especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia. However, compounds emitted from the petals differed from compounds emitted by the anthophore. The anthophore emitted the monoterpenoids lilac aldehydes and alcohols, whereas, all other typical scent compounds (e.g. benzoids, other monoterpenoids) were emitted by the petals. Lilac aldehydes are known to be behaviourally very attractive for noctuid moths, and they may serve as nectar guides in S. latifolia.     

Inflorescence scent,color, and nectar properties of “butterfly bush” (Buddleja davidii) in its native range

In this study, flower color, nectar properties, and inflorescence scent composition of eight natural and one introduced Buddleja davidii populations were investigated. Flower color of B. davidii was determined using the Royal Horticultural Society Color Chart and ranged from purple to white. Volume of nectar produced by a single flower ranged from 0.36 μl to 0.64 μl and total sugar concentration produced by inflorescence ranged from 17.0% to 33.5% in all populations. Floral nectar volume and sugar concentration were not significantly different between two flower color morphs in the B. davidii populations. Floral scents of B. davidii were collected using dynamic headspace adsorption and identified with coupled gas chromatography and mass spectrometry. In total, 33 compounds were identified from the inflorescences of B. davidii. The identified scents were divided into five chemical classes based on their biosynthetic origin: irregular terpenes, monoterpenoids, sesquiterpenoids, fatty acid derivatives, and benzenoids. The scent profiles in all populations were dominated by few components, such as: 4-oxoisophorone, E,E-α-farnesene, and 1-octen-3-ol. Given that inflorescence scents from natural and introduced individuals coming from the same population have discrepant chemical composition, we infer that phenotype plasticity may mediate floral scent composition. Based on the comparison of present and other data available on floral scent in B. davidii, we conclude that inflorescence scent may serve as a specific signal helping to attract pollinating butterflies to locate flowers as nectar sources, and may have evolved in conjunction with the sensory capabilities of butterflies and moths as a specific group of pollinators.     

Floral volatiles play a key role in specialized ant pollination

Chemical signals emitted by plants are crucial to understand the ecology and evolution of plant–animal interactions. Scent is an important component of floral phenotype and represents a decisive communication channel between plants and floral visitors. Floral volatiles promote attraction of mutualistic pollinators and, in some cases, serve to prevent flower visitation by antagonists such as ants. Despite ant visits to flowers have been suggested to be detrimental to plant fitness, in recent years there has been a growing recognition of the positive role of ants in pollination. Nevertheless, the question of whether floral volatiles mediate mutualisms between ants and ant-pollinated plants still remains largely unexplored. Here we review the documented cases of ant pollination and investigate the chemical composition of the floral scent in the ant-pollinated plant Cytinus hypocistis. By using chemical-electrophysiological analyses and field behavioural assays, we examine the importance of olfactory cues for ants, identify compounds that stimulate antennal responses, and evaluate whether these compounds elicit behavioural responses. Our findings reveal that floral scent plays a crucial role in this mutualistic ant–flower interaction, and that only ant species that provide pollination services and not others occurring in the habitat are efficiently attracted by floral volatiles. 4-oxoisophorone, (E)-cinnamaldehyde, and (E)-cinnamyl alcohol were the most abundant compounds in Cytinus flowers, and ant antennae responded to all of them. Four ant pollinator species were significantly attracted to volatiles emitted by Cytinus inflorescences as well as to synthetic mixtures and single antennal-active compounds. The small amount of available data so far suggest that there is broad interspecific variation in floral scent composition among ant-pollinated plants, which could reflect differential responses and olfactory preferences among different ant species. Many exciting discoveries will be made as we enter into further research on chemical communication between ants and plants.     

Floral scent in natural hybrids of Ipomopsis (Polemoniaceae) and their parental species

Background and Aims

Floral traits, such as floral volatiles, can contribute to pre-zygotic reproductive isolation by promoting species-specific pollinator foraging. When hybrid zones form, floral traits could also influence post-zygotic isolation. This study examined floral volatiles in parental species and natural hybrids in order to explore potential scent mediation of pre-zygotic and post-zygotic isolation.

Methods

Floral bouquets were analysed for the sister species Ipomopsis aggregata and I. tenuituba and their natural hybrids at two contact sites differing in both hybridization rate and temporal foraging pattern of hawkmoth pollinators. Floral volatiles were quantified in diurnal and nocturnal scent samples using gas chromatography–mass spectrometry.

Key Results

The bouquets of parental species and hybrids showed qualitative overlap. All flowers emitted similar sets of monoterpenoid, sesquiterpenoid, aliphatic and benzenoid compounds, but separated into groups defined by multivariate analysis of quantitative emissions. The parental species differed most strikingly in the nitrogenous compound indole, which was found almost exclusively in nocturnal bouquets of I. tenuituba. Natural hybrid bouquets were highly variable, and showed emission rates of several compounds that appeared transgressive. However, indole emission rates were intermediate in the hybrids compared with rates in the parents. Volatile bouquets at the contact site with lower hybridization did not show greater species specificity in overall scent emission, but I. tenuituba presented a stronger indole signal during peak hawkmoth activity at that site.

Conclusions

The two species of Ipomopsis differed in patterns of floral bouquets, with indole emitted in nocturnal I. tenuituba, but not in I. aggregata. Natural hybrid bouquets were not consistently intermediate between the parents, although hybrids were intermediate in indole emission. The indole signal could potentially serve as a hawkmoth attractant that mediates reproductive isolation both before and after hybrid formation.     

Variation of monoterpenoids inartemisia feddei andArtemisia scoparia

The composition and concentration of monoterpenoids in the leaves and stems ofArtemisia feddei andArtemisia scoparia were determined, and seasonal variation in the monoterpenoids ofArtemisia species were investigated. The two species possessed different compositions and concentrations of monoterpenoids. The total amount of monoterpenoid inA. scoparia was always higher than that of A.feddei, and the monoterpenoid yields of leaves were higher than stem yields in both species as compounds formed. The major constituents of A.scoparia were 25 while A.feddei consisted of 26 compounds. Sixteen common monoterpenoid compounds were found in both plants. Large differences in the relative amounts of the monoterpenoids were found between species and seasons. Extremely large differences in the relative amounts of naphtalene, sabinene, β-pinene, cyclohexene, and octatrine were found in the leaf monoterpenoids of the two species. The largest differences in relative amounts of stem monoterpenoids were in s abinene and β-pinene levels.     

Pollen advertisement: chemical contrasts between whole-flower and pollen odors

Odors of pollen and whole flowers were compared in taxonomically unrelated species that offer pollen as the only food reward to pollinators. Volatiles were collected using headspace adsorption and analyzed by gas chromatography and mass spectrometry. The odor of pollen was found to be chemically distinct from the total flower odor, and this pollen-odor distinctness varied among the three species. In Papaver rhoeas (Papaveraceae), the contrast between pollen and whole-flower odors was most subtle, with differences observed only in the proportions of individual volatiles (almost exclusively aliphatic hydrocarbons). In Filipendula vulgaris (Rosaceae), pollen volatiles were fewer than in the flowers (comprising mainly benzenoids and fatty-acid derivatives) and their relative proportions produced an odor dominated by 2-heptadecanone that contrasted strikingly with the flower odor dominated by 2-phenyl ethanol. In Lupinus polyphyllus (Fabaceae), the pollen odor contained fewer volatiles and in differing proportions than the flower fragrance (comprising almost exclusively isoprenoids). The findings add to earlier chemical evidence of odor contrasts between pollen and other flower parts in two other species. Drawing on information from pollination studies of these various species, it is suggested that pollen odor is used by pollen-foraging insects both to discriminate between plant species and to assess reward availability in individual flowers, and that it might in addition serve a protective function against destructive flower-feeding insects and pathogens.     

Floral scent in bird- and beetle-pollinated Protea species (Proteaceae): Chemistry,emission rates and function

Evolutionary shifts between pollination systems are often accompanied by modifications of floral traits, including olfactory cues. We investigated the implications of a shift from passerine bird to beetle pollination in Protea for floral scent chemistry, and also explored the functional significance of Protea scent for pollinator attraction. Using headspace sampling and gas chromatography–mass spectrometry, we found distinct differences in the emission rates and chemical composition of floral scents between eight bird- and four beetle-pollinated species. The amount of scent emitted from inflorescences of beetle-pollinated species was, on average, about 10-fold greater than that of bird-pollinated species. Floral scent of bird-pollinated species consists mainly of small amounts of “green-leaf volatiles” and benzenoid compounds, including benzaldehyde, anisole and benzyl alcohol. The floral scent of beetle-pollinated species is dominated by emissions of linalool, a wide variety of other monoterpenes and the benzenoid methyl benzoate, which imparts a fruity odour to the human nose. The number of compounds recorded in the scent of beetle-pollinated species was, on average, greater than in bird-pollinated species (45 versus 29 compounds, respectively). Choice experiments using a Y-maze showed that a primary pollinator of Protea species, the cetoniine beetle Atrichelaphinis tigrina, strongly preferred the scent of inflorescences of the beetle-pollinated Protea simplex over those of the bird-pollinated sympatric congener, Protea roupelliae. This study shows that a shift from passerine bird- to insect-pollination can be associated with marked up-regulation and compositional changes in floral scent emissions.     

Chemical composition of the wood and leaf oils from the “Clanwilliam Cedar” (Widdringtonia cedarbergensis J.A. Marsh): A critically endangered species

Widdringtonia is the only genus of the 16 genera of Cupressaceae present in South Africa. This genus is represented by three species in South Africa; W. nodiflora, W. schwarzii and W. cedarbergensis (= W. juniperoides) and the latter listed as critically endangered. Cedarwood oil (generally obtained from Juniperus species) is widely used as a fragrance material in several consumer products, however, no data has been published on the volatiles of the Clanwilliam cedar (W. cedarbergensis) native to South Africa. The essential oil composition of the wood and leaf oil isolated by hydro-distillation were analysed by GC–MS. The two oils were distinctly different. Twenty compounds representing 93.8% of the total oil were identified in the leaf oil which was dominated by terpinen-4-ol (36.0%), sabinene (19.2%), γ-terpinene (10.4%), α-terpinene (5.5%) and myrcene (5.5%). Twenty six compounds representing 89.5% of the total were identified in the wood oil with the predominance of thujopsene (47.1%), α-cedrol (10.7%), widdrol (8.5%) and cuparene (4.0%).     

Electroantennogram (EAG) responses of Microplitis croceipes and Cotesia marginiventris and their lepidopteran hosts to a wide array of odor stimuli: Correlation between EAG response and degree of host specificity?

In order to test whether the electroantennogram (EAG) response spectrum of an insect correlates to its degree of host specificity, we recorded EAG responses of two parasitoid species with different degrees of host specificity, Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), to a wide array of odor stimuli including compounds representing green leaf volatiles (GLVs), herbivore-induced plant volatiles (HIPV), ecologically irrelevant (not used by the parasitoid species and their hosts for host location) plant volatiles, and host-specific odor stimuli (host sex pheromones, and extracts of host caterpillar body and frass). We also tested the EAG responses of female moths of the caterpillar hosts of the parasitoids, Heliothis virescens and Spodoptera exigua, to some of the odor stimuli. We hypothesized that the specialist parasitoid will have a narrower EAG response spectrum than the generalist, and that the two lepidopteran species, which are similar in their host plant use, will show similar EAG response spectra to plant volatiles. As predicted, the specialist parasitoid showed greater EAG responses than the generalist to host-specific odor and one HIPV (cis-3-hexenyl butyrate), whereas the generalist showed relatively greater EAG responses to the GLVs and unrelated plant volatiles. We detected no differences in the EAG responses of H. virescens and S. exigua to any of the tested odor.     

Floral sesquiterpenes and their synthesis in dioecious kiwifruit

Kiwifruit species are vigorously growing dioecious vines that rely on bees and other insects for pollen transfer between spatially separated male and female individuals. Floral volatile terpene cues for insect pollinator attraction were characterized from flowers of the most widely grown and economically important kiwifruit cultivar Actinidia deliciosa ‘Hayward’ and its male pollinator ‘Chieftain’. The sesquiterpenes α-farnesene and germacrene D dominated in all floral tissues and the emission of these compounds was detected throughout the day, with lower levels at night. Two terpene synthase (TPS) genes were isolated from A. deliciosa petals that produced (+)-germacrene D and (E,E)-α-farnesene respectively. Both TPS genes were expressed in the same tissues and at the same times as their corresponding floral volatiles. Here we discuss these results with respect to plant and insect ecology and the evolution and structure of sesquiterpene synthases.Key words: terpene, dioecy, kiwifruit, volatile, ecology, evolution, flower     

The chemical nature of fetid floral odours in stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae)

By emitting strong fetid scents, sapromyiophilous flowers mimic brood and food sites of flies to attract them as pollinators. To date, intensive comparative scent analyses have been restricted to sapromyiophilous Araceae. Here, we analysed flower volatiles of fetid stapeliads to improve our understanding of the floral biology of fly pollinated species, and to learn whether mimicry types comparable to those found in Araceae exist. Floral volatiles of 15 species out of 11 genera within the Asclepiadoideae-Ceropegieae-Stapeliinae were collected via headspace adsorption and thermal desorption and analysed by gas chromatography-mass spectometry (GC-MS). Data were analysed using CNESS-NMDS statistics. Sapromyiophilous stapeliads are highly diverse in their scent composition, in which sulphur compounds, benzenoids, fatty acid derivatives or nitrogen-containing compounds dominate. Four groups are evident: species with high p-cresol content but low amounts of polysulphides (herbivore faeces mimicry); species with mainly polysulphides and low amounts of p-cresol (carnivore/omnivore faeces or carcass mimicry); species with high amounts of heptanal and octanal (carnivore/omnivore faeces or carcass mimicry); and species with hexanoic acid (urine mimicry). Considering the findings in the unrelated Araceae, our results support the universality of different mimicry types that are obviously subsumed under the sapromyiophilous syndrome.