Nepetalactone Isomers Research Articles

Integrative multivariate analysis of agro-chemical and genotypic traits in Indian catmint (Nepeta cataria L.) half-sib populations

This investigation conducted a comprehensive multivariate analysis on thirty half-sib populations of Nepeta cataria L., derived from natural populations based on oil yield. The study addresses the lack of comprehensive data on genetic, phenotypic, and chemical diversity in Nepeta cataria, which is essential for material selection and for conducting effective breeding programs. A substantial amount of phenotypic diversity was observed for all eleven quantitative traits measured in the present study. The phenotypic diversity was assessed using Euclidean distance-based agglomerative hierarchical clustering and principal component analysis (PCA) which showed more than 50 % diversity existing among the studied populations. These methods delineated the populations into three primary clusters, where herb yield was a key discriminator. The GC and GC/MS-based chemical profiling of these populations identified eleven major phytochemicals. Though, significant variances in the concentrations of various nepetalactone isomers were noted, correlating with the phenotypic clusters, the major differentiation was observed for cis-trans Nepetalactone (73.45%–93.20 %). Three distinct chemical clusters were defined, each characterized by unique chemical signatures. Molecular diversity was evaluated using 21 Start Codon Targeted Polymorphic (SCoT) and 20 CAAT box-derived DNA Polymorphic (CBDP) markers, revealing high levels of polymorphism. Populations were again grouped into three clusters. A correlative Mantel test performed to determine the association between agro-chemical and genotypic traits revealed minimal correlation between them, indicating a complex interplay between genetic makeup and phenotypic traits across these populations. This study underscores the genetic and chemical diversity within Nepeta cataria half-sib populations, providing insights that could influence future breeding and conservation efforts. The distinct clustering based on agronomic, chemical, and genotypic data highlights the potential for targeted selection and breeding programs within this species. Future research should focus on integrating these findings into breeding strategies for enhancing commercial cultivation.

Phytochemical diversity within a plant population of Nepeta crassifolia species: A rich source of nepetalactone in Iran

AbstractInvestigation of genetic diversity between and within populations is the first step in plant breeding programs. The present study focused on the phytochemical variation of essential oils of half‐sib families within a plant population of Nepeta crassifolia species, collected from north of Tehran province, Iran. Air‐dried aerial parts of several half‐sib progenies were water distilled to extract their essential oils. Quantification and qualification of the essential oils constituents were carried out using gas chromatography (GC) and gas chromatography coupled to mass spectrometry (GC/MS). Dried plant materials, yielded from 0.09% to 0.73% (v/w) of essential oils. In half‐sib families between 9 and 19 compounds were observed. In all of the studied families the extracted oils were predominated by oxygenated monoterpenes, and regarding the main phytochemical components, three chemotypes were recognized in the studied population. In most of the half‐sib families, 4aα,7α,7aβ‐nepetalactone isomer was dominant composition (38.7%–87.6%), while in two families 4aα,7α,7aα‐nepetalactone isomer (41.6%) and 1,8‐cineol (42.1%) were dominant constitutes. Significant correlation was not seen between biomass, essential oil yield and nepetalactone isomers. Comparing the presented results with essential oil components of other Nepeta species, such as N. cataria, revealed that N. crassifolia can be considered as a commercial source of nepetalactone isomers. Thus, promoting domestication and cultivation of N. crassifolia as industrial and medicinal species should be noticed.

Repellency Assessment of Nepeta cataria Essential Oils and Isolated Nepetalactones on Aedes aegypti

There is an increased need for improved and affordable insect repellents to reduce transmission of rapidly spreading diseases with high mortality rates. Natural products are often used when DEET cannot be afforded or accessed and when consumers choose not to use a synthetic repellent. The essential oils from two newly bred Nepeta cataria (catnip) plants representing two different chemotypes and their respective isolated nepetalactone isomers were evaluated as mosquito repellents against Aedes aegypti mosquitoes that transmit the Zika and Dengue virus in a one choice landing rate inhibition assay. A dose response curve was generated for each treatment and a time course analysis of repellency was performed over 24 hours with a N. cataria essential oil sample. The results indicate that all essential oil samples and their respective purified nepetalactone isomers were able to achieve greater than 95% repellency. Between two and four hours, the ability to repel more than 95% of the mosquitoes diminished. At the lowest concentrations tested, the nepetalactones and crude essential oil samples were more effective than DEET at reducing the number of mosquito landings.

Chemical composition of the essential oils of Nepeta laevigata and Nepeta elliptica from India

The genus Nepeta (Lamiaceae), also called Glechoma and Cataria, is a multiregional genus and consists of about 250 species of perennial herbs distributed in central and southern parts of Europe, Asia, and the Middle East [1–3]. These plants are commonly known as catmint [4], and about 30 species occur in India. Many Nepeta species have been reported to be biologically active and are used in folk medicine because of their spasmodic, diuretic, antiseptic, antitussive, antiasthmatic, and febrifuge activities [5–9]. Several Nepeta species are also reported to reduce serum lipids and to possess anti-inflammatory effects [10, 11]. Most Nepeta species are rich in essential oils, and various biologically active iridoids/monoterpene nepetalactones have been reported in several Nepeta species possessing diverse biological activities, viz., feline attractant, canine attractant, insect repellant, arthropod defense [12, 13], antibacterial, antifungal, and antiviral activities [14]. N. laevigata and N. elliptica are distributed through Afghanistan, China, Nepal, Pakistan, and India. In India, the two plant species are largely confined to Himachal Pradesh, Jammu and Kashmir, and Uttar Pradesh. Nepeta laevigata, also known as Betonica laevigata, is a perennial aromatic herb that grows to a height of 80 cm, is white pubescent, and has petiole 2–12 mm and leaf blade ovate to triangular, while N. elliptica is a small ascending or flexuous herb, 30–60 cm high. Both N. laevigata and N. elliptica are used in traditional medicine. Nepeta laevigata, is reported to be used locally in fevers and for sore throat, while, as an infusion of the seeds, N. elliptica is used in dysentery. According to our finding, there is no report on the chemical compostion of the essential oil of N. laevigata and N. elliptica growing in J & K, India, so the aim of the present work was to compare the chemical composition of these two Nepeta species. The chemical constituents of the volatile oils were analyzed by capillary GC-FID and GC-MS. The components of the oils of the air-dried aerial parts of N. laevigata and N. elliptica are listed in Table 1 with their percentages and relative retention indices (RRI). The different chemical constituents of the essential oils are listed in order of their elution from an RTX-5 column. As shown, 24 components belonging to different class of compounds were identified in the oil of N. laevigata, making up 86.7% of the total oil. -Citronellol (16.5%), germacrene D (19.4%), -caryophyllene (10.8%), -bisabolol oxide B (12.4%), -bourbonene (4.5%), -humulene (3.5%), spathulenol (3.9%), and -bisabolol (5.3%) were the major ones. Other constituents such as 4a,7,7a-nepetalactone (2.0%), allo-aromadendrene (1.1%), and caryophyllene oxide (3.2%) were present in small amounts. In addition, some other constituents such as -pinene, 1,8-cineole, linalool, geraniol, citronellyl acetate, etc. were present in trace amounts. The essential oil composition is dominated by the presence of sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and oxygenated monoterpenes constituting 40.9%, 25.1%, and 20.7%, respectively, of the total oil composition. Of the various nepetalactone isomers, viz., 4a,7,7a-nepetalactone, 4a,7,7a-nepetalactone, and 4a,7,7a-nepetalactone, which have been labeled as the biochemical markers of the Nepeta essential oils and are very useful in chemotaxonomic studies, only one nepetalactone isomer viz., 4a, 7, 7a-nepetalactone, as a minor constituent, was present in the essential oil of Nepeta laevigata. -Caryophyllene, which is one of the major constituents of the essential oil, has been reported in some Nepeta species such as N. depauperata [15], N. flavida [16], and N. nuda [17] as the major component. Likewise, germacrene-D, the other major constituent of the oil sample, has also been reported in various other Nepeta species such as Nepeta macrosiphon [18] and Nepeta sintensii [19]. In addition, the other major components such as -bourbonene and spathulenol have been reported in N.depauperata [15], N. macrosiphon [18], and N. sintensii [19].

Repellent activity of catmint, Nepeta cataria, and iridoid nepetalactone isomers against Afro-tropical mosquitoes, ixodid ticks and red poultry mites

The repellent activity of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), and the main iridoid compounds (4a S,7 S,7a R) and (4a S,7 S,7a S)-nepetalactone, was assessed against (i) major Afro-tropical pathogen vector mosquitoes, i.e. the malaria mosquito, Anopheles gambiae s.s. and the Southern house mosquito, Culex quinquefasciatus, using a World Health Organisation (WHO)-approved topical application bioassay (ii) the brown ear tick, Rhipicephalus appendiculatus, using a climbing repellency assay, and (iii) the red poultry mite, Dermanyssus gallinae, using field trapping experiments. Gas chromatography (GC) and coupled GC–mass spectrometry (GC–MS) analysis of two N. cataria chemotypes (A and B) used in the repellency assays showed that (4a S,7 S,7a R) and (4a S,7 S,7a S)-nepetalactone were present in different proportions, with one of the oils (from chemotype A) being dominated by the (4a S,7 S,7a R) isomer (91.95% by GC), and the other oil (from chemotype B) containing the two (4a S,7 S,7a R) and (4a S,7 S,7a S) isomers in 16.98% and 69.83% (by GC), respectively. The sesquiterpene hydrocarbon ( E)-(1 R,9 S)-caryophyllene was identified as the only other major component in the oils (8.05% and 13.19% by GC, respectively). Using the topical application bioassay, the oils showed high repellent activity (chemotype A RD 50 = 0.081 mg cm −2 and chemotype B RD 50 = 0.091 mg cm −2) for An. gambiae comparable with the synthetic repellent DEET (RD 50 = 0.12 mg cm −2), whilst for Cx. quinquefasciatus, lower repellent activity was recorded (chemotype A RD 50 = 0.34 mg cm −2 and chemotype B RD 50 = 0.074 mg cm −2). Further repellency testing against An. gambiae using the purified (4a S,7 S,7a R) and (4a S,7 S,7a S)-nepetalactone isomers revealed overall lower repellent activity, compared to the chemotype A and B oils. Testing of binary mixtures of the (4a S,7 S,7a R) and (4a S,7 S,7a S) isomers across a range of ratios, but all at the same overall dose (0.1 mg), revealed not only a synergistic effect between the two, but also a surprising ratio-dependent effect, with lower activity for the pure isomers and equivalent or near-equivalent mixtures, but higher activity for non-equivalent ratios. Furthermore, a binary mixture of (4a S,7 S,7a R) and (4a S,7 S,7a S) isomers, in a ratio equivalent to that found in chemotype B oil, was less repellent than the oil itself, when tested at two doses equivalent to 0.1 and 0.01 mg chemotype B oil. The three-component blend including ( E)-(1 R,9 S)-caryophyllene at the level found in chemotype B oil had the same activity as chemotype B oil. In a tick climbing repellency assay using R. appendiculatus, the oils showed high repellent activity comparable with data for other repellent essential oils (chemotype A RD 50 = 0.005 mg and chemotype B RD 50 = 0.0012 mg). In field trapping assays with D. gallinae, addition of the chemotype A and B oils, and a combination of the two, to traps pre-conditioned with D. gallinae, all resulted in a significant reduction of D. gallinae trap capture. In summary, these data suggest that although the nepetalactone isomers have the potential to be used in human and livestock protection against major pathogen vectors, intact, i.e. unfractionated, Nepeta spp. oils offer potentially greater protection, due to the presence of both nepetalactone isomers and other components such as ( E)-(1 R,9 S)-caryophyllene.

Repellent activity of Nepeta grandiflora and Nepeta clarkei (Lamiaceae) against the cereal aphid, Sitobion avenae (Homoptera: Aphididae)

Nepeta spp. (Lamiaceae) contain principally the nepetalactone isomers (4a S,7 S,7a R) and (4a S,7 S,7a S)-nepetalactone, which are also known to comprise aphid sex pheromones and aphid parasitoid attractants. Previous studies have shown that Nepeta cataria can be grown as a non-food crop for the commercial-scale production of (4a S,7 S,7a R)-nepetalactone in high purity, thus removing requirement for highly demanding stereocontrolled synthesis. Furthermore, previous literature reports have suggested that Nepeta spp., other than the widely studied N. cataria, can produce a diverse range of natural products other than nepetalactones, including high value sesquiterpenes. Thus, with the aim of identifying alternative Nepeta spp. for production of high value semiochemicals, the essential oils of two readily available species, Nepeta grandiflora and N. clarkei, were collected by steam distillation and analysed using high resolution gas chromatography (GC) and coupled GC–mass spectrometry (GC–MS). Analysis of the oils surprisingly revealed a very low nepetalactone content, but instead the presence of predominantly sesquiterpene compounds, and, for N. clarkei, the major component, geranyl acetate. Amongst the compounds identified in both oils was ( S)-germacrene d, a previously reported potent arthropod repellent. To determine the potential crop protection value of these essential oils, the repellent activity of the oils was assessed using a four-way olfactometer assay, with both oils showing strong repellent effects. These findings illustrate that members of the Nepeta genus possess a diverse range of high value secondary metabolites, and also highlight their potential to be developed as renewable feedstocks for the production of repellents for use economically important crop pests, as well as for the production of sex pheromones and natural enemy attractants.

Nepetalactone Content and Antibacterial Activity of the Essential Oils from Different Parts of Nepeta persica

The essential oils from the flower, leaf, stem and root of Nepeta persica Boiss., analyzed by GC and GC/MS, were shown to contain 4abeta,7alpha,7abeta-nepetalactone (58.5%, 62.3%, 66.2% and 27.1%, respectively), and 4aalpha,7alpha,7abeta-nepetalactone (33.0%, 28.3%, 24.9% and 7.6%, respectively). The other main component of the flower and stem oils was alpha-pinene (3.6% and 4.4%) and of the leaf oil beta-ocimene (3.6%). In the root oil, other main constituents were alpha-pinene (40.4%), alpha-amorphene (5.3%), gamma-cadinene (2.9%), and cis-calamenene (2.5%). Nepetalactone was the major component of the flower, leaf and stem oils, which are thus important sources of nepetalactone. Antibacterial activities of the flower, leaf, stem and root oils were evaluated using the micro-dilution broth method. Inhibitory effects on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Enterococcus faecalis were recorded. The flower, leaf, stem, and root oils had difference activities against the test microorganisms. The antibacterial property of the essential oils might be ascribed to their high content of nepetalactone isomers.

Volatile constituents analysis of Nepeta cataria from central Iran

The genus Nepeta (Lamiaceae) comprises 250 species of perennial herbs that are distributed in Europe, Asia, North Africa, and the mountains of tropical Africa. These plants are commonly known as catmint [1]. The common Persian name of this genus is pune-sa, and about 67 species are recorded in Iran [2]. Many Nepeta species have some biological activity and are used in folk medicine because of their antispasmodic, diuretic, antiseptic, antitussive, antiasthmatic, and febrifuge activities [3–8]. Nepeta cataria L. (Lamiaceae) is one of the endemic species of this genus in Iran. N. cataria, commonly known as catnip, is native to Asia Minor and Southeast Europe and grows to a height of 90 cm. It is used as a fortifier, a disinfectant, and a cure against cold [1, 9]. Literature surveys reveal that most oils of Nepeta species such as N. cataria contain nepetalactones as the main component. Antibacterial, fungicidal, and antiviral activities have been attributed to nepetalactones [3, 6, 10]. According to our finding, there is no report on the chemical composition of the essential oil of N. cataria growing in central Iran, so the aim of the present research was to determine the chemical composition of N. cataria essential oil. The constituents of the volatile oil were analyzed by gas chromatography (GC) and gas chromatography–mass spectroscopy (GC–MS). The components of the oil of air-dried herbal parts of N. cataria are listed Table 1, including percentages and retention indices of the components. Constituents are listed in order of their elution from an HP-5MS column. As is shown, nine compounds were identified in the oil of N. cataria, making up 98.0% of the total oil. Among the constituents of the volatile oil, 4aα,7α,7aα-nepetalactone (87.1%), 4aα,7α,7aβ-nepetalactone (3.1%), β-caryophyllene (2.5%), and β-pinene (1.7%) were the major ones; the other constituents were present in relatively small amounts, representing only (3.6%) of the total oil. Nepetalactone isomers, which are the major constituens in our oil, were present in the essential oil of several Nepeta spp [11–20]. It was found that nepetalactones were responsible for the feline attractant properties of Nepeta species. 4aα,7α,7aα-Nepetalactone, which was the main component of our oil, has been detected as the major one in four Nepeta species growing in Turkey [21] and also in N. cataria growing in Germany [22], while caryophyllene oxide, which was abundant in N. cataria from Lebanon [23] and Lithuania [24] (6.4%, 7.3% respectively), was not found in our work. β-Caryophyllene, which was the third major component of our oil, has been reported in the oil of some Nepeta species such as N. cataria [23], N. daenensis [25], and N. fissa from Iran [26], and in N. curviflora growing in Lebanon [23]. On the other hand, 1,8-cineole, which was the most abundant component in many Nepeta species [4, 27–30], was not present in our work. Also, linalool and germacrene D have been identified in sizable amounts in other Nepeta species [4, 29, 31, 32], but traces of these compounds were found as oil constituents in this study. This is not unexpected since plants often manufacture different amounts of phytochemicals when grown in different geographical locations. The aerial parts (leaves and flowers/inflorescences) of Nepeta cataria L. growing wildly in the Kashan area (Isfahan Province, Central Iran) at an altitude of ca. 1550 m were collected in July 2007 and were dried in the shade (at room temperature). Voucher specimens of the plant were deposited in the Herbarium of Kashan Botanical Garden, Research Institute of Forests and Rangelands, Kashan, Iran. The air-dried aerial parts of the plant (130 g) subjected to volatile fractionation were isolated by hydrodistillation using an all-glass Clevenger-type apparatus for 3.5 h according to the method recommended in the European Pharmacopoeia [33]. After decanting and drying of the pale yellow oil (0.89%) over anhydrous sodium sulfate, it was stored in vials at low temperature (4°C) before analysis.

Essential Oil Composition of Four Iranian Nepeta Species (N. cephalotes, N. bornmuelleri, N. mirzayanii and N. bracteata)

Essential oils from aerial parts of Nepeta cephalotes Boiss., N. bornmuelleri Hausskn. ex Bornm., N. mirzayanii Rech. f. et Esfand. and N. bracteata Benth. were obtained by hydrodistillation. The oils were analyzed by capillary gas chromatography, using fame ionization and mass spectrometric detection. Eight components were identified in the oil of N. cephalotes with 4aα,7α,7aα-nepetalactone (90.1%) and β-pinene (7.5%) as main constituents. Twenty-eight compounds were identified in the oil of N. bornmuelleri with 4aβ,7α,7aβ-nepetalactone (64.0%) and 1,8-cineole (7.1%) as main components. Twenty-two compounds were characterized in the oil of N. mirzayanii with 4aα,7α,7aα-nepetalactone (61.0%) and caryophyllene oxide (7.8%) as main constituents. Twenty-eight compounds were characterized in the oil of N. bracteata with spathulenol (14.0%), caryophyllene oxide (12.3%), bicyclogermacrene (11.4%) and β-caryophyllene (11.2%) as main constituents. The results showed the nepetalactone isomers were the main components of the oils of N. cephalotes, N. bornmuelleri and N. mirzayanii. The oil of N. bracteata consisted of mainly of sesquiterpenes, while nepetalactone was not detected in this oil.

Chemical composition of the essential oil of five Iranian Nepeta species (N. crispa, N. mahanensis, N. ispahanica, N. eremophila and N. rivularis)

AbstractEssential oils from aerial parts of Nepeta crispa Willd., Nepeta mahanensis Jamzad & Simmonds, Nepeta ispahanica Boiss., Nepeta eremophila Hausskn. & Bornm. and Nepeta rivularis Bornm. were obtained by hydro‐distillation. The oils were analyzed by capillary gas chromatography, using flame ionization and mass spectrometric detection. Twenty‐eight components were identified in the oil of Nepeta crispa with 1,8‐cineole (62.8%), 4aα‐7α‐7aα‐nepetalactone (10.3%) and 4aβ‐7α‐7aβ‐nepetalactone (9.2%) as main constituents. Eighteen compounds were identified in the oil of Nepeta mahanensis with nepetalactone (37.6%), 1,8‐cineole (27.2%) and germacrene D (6.5%) as the main components. Twenty‐seven compounds were characterized in the oil of Nepeta ispahanica with 1,8‐cineole (71.7%) as the main constituent. Twenty‐six compounds were characterized in the oil of Nepeta eremophila with 4aβ‐7α‐7aβ‐nepetalactone (73.3%) and 1,8‐cineole (13.1%) as the main constituents. Twenty‐two components were identified in the oil of Nepeta rivularis with 1,8‐cineole (38.5%), sabinene (14.8%), β‐pinene (10.7%) and γ‐terpinene (5.1%) as the main constituents. The results showed that, although the nepetalactone isomers are the main components of the essential oils of N. mahanensis and N. eremophila, the oil of N. crispa consists of about 20% nepetalactone and the oils of other species have different compositions. 1,8‐Cineole was present in all oils at percentages of 13.1% (the lowest amount in N. eremophila) to 71.7% (the highest amount in N. ispahanica). Copyright © 2006 John Wiley & Sons, Ltd.

Essential Oil Composition of Nepeta involucrata from Iran

The essential oil of Nepeta involucrata (Bunge) Bornm. (Lamiaceae) obtained by hydrodistillation from the aerial parts during the flowering stage was analyzed by GC and GC-MS. Forty-eight compounds representing 97.2% of total oil were identified. The main compounds of the oil were 1,8-cineol (23.1%), germacrene-D (15.1%), and β-pinene (12.2%). No traces of nepetalactone isomers were found as oil constituents.

Feeding Deterrent Effects of Catnip Oil Components Compared with Two Synthetic Amides Against <I>Aedes aegypti</I>

Recently, catnip, Nepeta cataria L. (Lamiaceae), essential oil has been formulated and marketed as an alternative repellent for protection against biting arthropods by several vendors. We isolated the major active components of catnip oil, E,Z- and Z,E-nepetalactone, and quantitatively measured their antibiting efficacy compared with the repellents N,N-diethyl-3-methylbenzamide (deet) and chiral (1S,2'S)-2-methylpiperidinyl-3-cyclohexene-1-carboxamide (SS220) against the yellowfever mosquito, Aedes aegypti (L.), by using an in vitro assay and human volunteers at 24 nmol compound/cm2 (cloth or skin). Of all compounds tested in an in vitro assay, SS220 ranked as the most effective, whereas catnip oil and the nepetalactone compounds did not differ significantly from each other or from deet. However, in human volunteer bioassays, neither E,Z and Z,E-nepetalactone nor racemic nepetalactone deterred mosquito biting as effectively as SS220 or deet. All compounds differed significantly from the control. We conclude that catnip oil and nepetalactone isomers are significantly less effective than deet or SS220 in deterring the biting of Ae. aegypti.

Volatile constituents of the essential oil ofNepeta ucrainica L. ssp.kopetdaghensis from Iran

Composition of the volatile oil of Nepeta ucraininca L. ssp. kopetdaghensis (Lamiaceae) was investigated by GLC and GC-MS. Forty-one compounds representing 89.5% of the total oil were characterized. The main components of the oil were germacrene-D (39.7%), palmitic acid (10.8%), β-bourbonene (5.8%) and spathulenol (5.6%). Nepetalact-one isomers were not present in the essential oil of N. ucrainica L. ssp. kopetdaghensis. Copyright © 2004 John Wiley & Sons, Ltd.

Analysis of the volatile constituents of Nepeta macrosiphon Boiss. grown in Iran

AbstractComposition of the volatile oil of Nepeta macrosiphon Boiss. (Lamiaceae) was investigated by GLC and GC–MS. Seventy‐three components, representing 96.9% of the total oil, were characterized. The main components of the oil were spathulenol (28.8%), α‐cadinol (13.6%), bicyclogermacrene (10.1%), β‐caryophyllene (9.6%) and linalool (5.6%). Nepetalactone isomers were not present in the essential oil of N. macrosiphon. Copyright © 2004 John Wiley & Sons, Ltd.

Functional specialisation and polyphenism in aphid olfactory sensilla

Electroantennogram (EAG) responses to the aphid sex pheromone components, (1 R,4a S,7 S,7a R)-nepetalactol and (4a S,7 S,7a R)-nepetalactone, and a plant volatile, (E)-2-hexenal, were investigated at three different positions (5/6th, 4/5th and 3/4th inter-segmental regions) along the antennae of four different morphs in two host-alternating aphid species, Aphis fabae Scopoli and Rhopalosiphum padi (L.). Position-dependent and morph-specific EAG responses were elicited in both species. The nepetalactol and nepetalactone isomers elicited large EAG responses at all three recording positions in males of both species, such that primary rhinaria as well as secondary rhinaria appeared to respond. Asexual female morphs showed relatively smaller EAG responses to these compounds. The secondary rhinaria, which have been reported as sex pheromone receptors in males, were not very different in their number and distribution between gynoparae and alate virginoparae, but the gynoparae showed significantly larger EAG responses to nepetalactol and nepetalactone. The alate virginoparae showed EAG responses that were similar to those of apterous virginoparae, which lack secondary rhinaria. Taking the EAG response profiles together with the distribution of the secondary rhinaria, it is suggested that the function of secondary rhinaria differs between the morphs. Secondary rhinaria appear to detect sex pheromone components in males and gynoparae but not in the alate virginoparae. If they are functional in the latter morph, they are likely to play a role in detecting specific, but as yet unknown, volatile compounds. Some 30 plant volatiles were tested but none evoked an EAG response that could be allocated to the secondary rhinaria. In contrast to the very different EAG response profiles to the pheromone compounds between morphs, EAG responses to (E)-2-hexenal were similar in all forms and both species. These findings suggest that this plant volatile was detected only by the two primary rhinaria, which are common to all morphs. The present study showed that EAG responses were not a simple summation of receptor potentials between recording and reference electrodes in aphids. The localised distribution pattern of olfactory receptor neurones around the recording electrode was also likely to contribute to the EAG responses.

The aphid sex pheromone

Abstract