Analyses of lepidopteran sex pheromones by mass spectrometry

Structure, Synthesis, and Bioassays of Sex Pheromone for Pyrausta machaeralis (Lepidoptera: Crambidae)

The leaf skeletonizer, Pyrausta machaeralis (Lepidoptera: Crambidae), is a serious insect pest of teak (Tectona grandis) in China. The application of insect pheromones is widely applied as an environmentally friendly technology for integrated pest management (IPM). In the present study, crude extracts of sex pheromone glands of calling P. machaeralis females were collected and then analyzed using gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography-mass spectrometry (GC-MS). The combination of infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectrometry was used for structure identification. Afterward, their electrophysiological and behavioral activity was evaluated in the laboratory and field. Herein, we eventually determined two active components, E-11-tetradecenyl acetate (E11-14:Ac) and Z-11-tetradecenyl acetate (Z11-14:Ac), at a ratio of 96:4, as the sex pheromone of P. machaeralis. The identification of sex pheromones would facilitate the development of efficient strategies for monitoring and controlling the field populations of P. machaeralis.

Functional characterization of sex pheromone receptors in Spodoptera frugiperda, S. exigua, and S. litura moths

Moths possess an extremely sensitive and diverse sex pheromone processing system, in which pheromone receptors (PRs) are essential to ensure communication between mating partners. Functional properties of some PRs are conserved among species, which is important for reproduction. However, functional differentiation has occurred in some homologous PR genes, which may drive species divergence. Here, using genome analysis, 17 PR genes were identified from Spodoptera frugiperda, S. exigua, and S. litura, which belong to 6 homologous groups (odorant receptor [OR]6, 11, 13, 16, 56, and 62); of which 6 PR genes (OR6, OR11, OR13, OR16, OR56, and OR62) were identified in S. frugiperda and S. exigua, and 5 PR genes were identified in S. litura, excluding OR62. Using heterologous expression in Xenopus oocytes, we characterized the functions of PR orthologs including OR6, OR56, and OR62, which have not been clarified in previous studies. OR6 orthologs were specifically tuned to (Z,E)-9,12-tetradecadienyl acetate (Z9,E12-14:OAc), and OR62 orthologs were robustly tuned to Z7-12:OAc in S. frugiperda and S. exigua. The optimal ligand for OR56 was Z7-12:OAc in S. frugiperda, but responses were minimal in S. exigua and S. litura. In addition, SfruOR6 was male antennae-specific, whereas SfruOR56 and SfruOR62 were male antennae-biased. Our study further clarified the functional properties of PRs in 3 Spodoptera moth species, providing a comprehensive understanding of the mechanisms of intraspecific communication and interspecific isolation in Spodoptera.

Genome-Wide Identification and Expression Profiling of Candidate Sex Pheromone Biosynthesis Genes in the Fall Armyworm (Spodoptera frugiperda)

Spodoptera frugiperda is an agricultural pest causing substantial damage and losses to commercial crops. Sex pheromones are critical for successful mating in Lepidoptera and have been used for monitoring and control of many pest species. The sex pheromone of S. frugiperda is known, but the genes involved in its biosynthesis have not been identified. We systematically studied 99 candidate sex pheromone genes in the genome of S. frugiperda including 1 acetyl-CoA carboxylase (ACC), 11 fatty acid synthases (FASs), 17 desaturases (DESs), 4 fatty acid transport proteins (FATPs), 29 fatty acyl-CoA reductases (FARs), 17 acetyl-CoA acetyltransferases (ACTs), 5 acyl-CoA dehydrogenase (ACDs), 3 enoyl-CoA hydratases (ECHs), 3 hydroxyacyl-CoA dehydrogenases (HCDs), 6 ethyl-CoA thiolases (KCTs), and 3 acyl-CoA-binding proteins (ACBPs). Based on the comparative transcriptome results, we found 22 candidate sex pheromone biosynthesis genes predominately expressed in pheromone glands (PGs) than abdomens without PGs including SfruFAS4, SfruFATP3, SfruACD5, SfruKCT3, SfruDES2, SfruDES5, SfruDES11, SfruDES13, SfruFAR1, SfruFAR2, SfruFAR3, SfruFAR6, SfruFAR7, SfruFAR8, SfruFAR9, SfruFAR10, SfruFAR11, SfruFAR14, SfruFAR16, SfruFAR29, SfruACT6, and SfruACT10. A combination of phylogenetic and tissue-specific transcriptomic analyses indicated that SfruDES5, SfruDES11, SfruFAR2, SfruFAR3, and SfruFAR9 may be key genes involved in the sex pheromone synthesis of S. frugiperda. Our results could provide a theoretical basis for understanding the molecular mechanisms of sex pheromone biosynthesis in S. frugiperda, and also provide new targets for developing novel pest control methods based on disrupting sexual communication.

Newly Discovered Components of Dendrolimus pini Sex Pheromone

The pine-tree lappet moth, D. pini, is a harmful defoliator of pine forests in Europe and Asia and a potentially invasive species in North America. The lures for trapping D. pini males based on two known components of its sex pheromone appeared weakly attractive to male moths. Identification of all components of the sex pheromone might allow for the development of more effective lures. The pheromone was sampled from virgin females using SPME and analyzed using gas chromatography coupled with mass spectrometry. Four new likely components ((Z5)-dodecenal, (Z5)-dodecen-1-ol, (Z5)-decen-1-yl acetate, (Z5)-tetradecen-1-yl acetate) and two known components ((Z5,E7)-dodecadienal, (Z5,E7)-dodecadien-1-ol) were identified based on comparison against authentic standards, Kováts indices and spectra libraries. The samples also contained several sesquiterpenes. Wind tunnel and field experiments showed that some blends of synthetic pheromone components alone or enriched with Scots pine essential oil (SPEO) were attractive to D. pini males. One component-(Z5)-decen-1-yl acetate-had a repelling effect. The presented knowledge of D. pini sex pheromone provides a basis for developing optimal lures for monitoring or controlling insect populations.

Identification and Field Evaluation of Sex Pheromone Components and Its Antagonist Produced by a Major Tea Pest, Archips strojny (Lepidoptera: Tortricidae)

Pesticide application is the only known control method for the tea tortrix Archips strojny (Lepidoptera: Tortricidae), which is a major pest of spring tea in China. To develop sex pheromone-based, environmentally safe control strategies, here we identified the sex pheromone components of this species. The male moths' antennae responded electrophysiologically to two compounds in female pheromone gland extracts. Gas chromatography-mass spectrometry analysis indicated that the two bioactive compounds were (Z)-11-tetradecenyl acetate (Z11-14:Ac) and (Z)-11-tetradecenyl alcohol (Z11-14:OH). Field trapping assays showed that lures baited with only the major component Z11-14:Ac were the most attractive to male moths, and the attractiveness decreased significantly when the lure was impregnated with increased relative ratios of the minor component Z11-14:OH. Our study demonstrated that Z11-14:Ac was the major attractant in the A. strojny sex pheromone, and the minor component Z11-14:OH seemed to serve as an antagonist. The results indicate that lures baited with 1 mg of Z11-14:Ac could be used as a monitoring or mass trapping tool for A. strojny management in Chinese tea plantations. Furthermore, Z11-14:Ac was identified as a common sex pheromone attractant of nine Archips species; these results lay the foundation for developing mating disruption techniques that target multiple leafroller pests.

Automated Surveillance of Lepidopteran Pests with Smart Optoelectronic Sensor Traps

Several lepidopterans are pests in horticulture and pose biosecurity risks to trading countries worldwide. Efficient species-specific semiochemical lures are available for some of these pests, facilitating the implementation of surveillance programmes via trapping networks. These networks have a long history of success in detecting incursions of invasive species; however, their reliance on manual trap inspections makes these surveillance programmes expensive to run. Novel smart traps integrating sensor technology are being developed to detect insects automatically but are so far limited to expensive camera-based sensors or optoelectronic sensors for fast-moving insects. Here, we present the development of an optoelectronic sensor adapted to a delta-type trap to record the low wing-beat frequencies of Lepidoptera, and remotely send real-time digital detection via wireless communication. These new smart traps, combined with machine-learning algorithms, can further facilitate diagnostics via species identification through biometrics. Our laboratory and field trials have shown that moths flying in/out of the trap can be detected automatically before visual trap catch, thus improving early detection. The deployment of smart sensor traps for biosecurity will significantly reduce the cost of labour by directing trap visits to the locations of insect detection, thereby supporting a sustainable and low-carbon surveillance system.

Cinnamomeoventrolide - Double Bond Regioisomerism in Frog Semiochemicals

Frogs of the families Mantellinae and Hyperoliidae possess male specific femoral or gular glands that are used during courtship. These glands release volatile compounds, e. g. the macrocyclic lactone gephyromantolide A (2,6,10-trimethyl-6-undecen-11-olide) in the case of Gephyromantis boulengeri (Mantellinae). During the analysis of the volatiles of Hyperolius cinnamomeoventris (Hyperoliidae) we detected an unknown compound A, which we called cinnamomeoventrolide, whose mass spectrum showed high similarity with the spectrum of gephyromantolide A. Nevertheless, slight spectral differences led to the proposal of a regioisomer of gephyromantolide A as a structure for A, 2,6,10-trimethyl-5-undecen-11-olide. A versatile synthesis of this compound was developed to allow access to all four stereoisomers from a single chiral starting material, the so-called (S)-Roche ester, using ring-closing metathesis as a key step. With these stereoisomers, the absolute configuration of the natural product was established to have the (2R,10S)-configuration by GC on a chiral phase. The configuration of natural gephyromantolide A is the opposite. Both frogs seem to use a similar biosynthetic pathway to access the target compounds, differing in the stereochemistry of the reduction steps, and requiring an additional isomerization in case of G. boulengeri. This unique regioisomeric differentiation of double bonds in semiochemicals has so far only been observed in insects. The compounds are likely to play a role in species-recognition of the frogs.

Identification and dynamic expression profiling of circadian clock genes in Spodoptera litura provide new insights into the regulation of sex pheromone communication

Spodoptera litura is an important pest that causes significant economic damage to numerous crops worldwide. Sex pheromones (SPs) mediate sexual communication in S. litura and show a characteristic degree of rhythmic activity, occurring mainly during the scotophase; however, the specific regulatory mechanisms remain unclear. Here, we employed a genome-wide analysis to identify eight candidate circadian clock genes in S. litura. Sequence characteristics and expression patterns were analyzed. Our results demonstrated that some circadian clock genes might regulate the biosynthesis and perception of SPs by regulating the rhythmic expression of SP biosynthesis-related genes and SP perception-related genes. Interestingly, all potential genes exhibited peak expression in the scotophase, consistent with the SP could mediate courtship and mating behavior in S. litura. Our findings are helpful in elucidating the molecular mechanism by which circadian clock genes regulate sexual communication in S. litura.

The scent chemistry of butterflies

Butterflies use structurally highly diverse volatile compounds for communication, in addition to visual signals. These compounds originate from plants or a formed de novo especially by male butterflies that possess specific scent organs.

Genes involved in the Type I pheromone biosynthesis pathway and chemoreception from the sex pheromone gland transcriptome of Dioryctria abietella

Dioryctria abietella is a coniferous seed orchard pest that can damage a series of host plants and cause huge losses to the forest economy. Sex pheromones play an important role in lepidopteran sex communication for reproduction and can be used as biological control agents to monitor and trap pests. However, the genes involved in the biosynthesis, transportation, and degradation of D. abietella sex pheromones have not been studied extensively. Transcriptome analysis of female D. abietella sex pheromone glands (PGs) revealed that 210 candidate genes might be involved in sex pheromone biosynthesis (139 genes) and chemoreception systems (71 genes). The gene expression patterns exhibited four desaturase genes (DabiDES4-7) and one fatty acid reductase gene (DabiFAR6), which were more highly expressed in sex pheromone glands than in other tissues, suggesting that these enzymes play an important role in D. abietella sex pheromone synthesis. In addition, most DabiOBPs showed high expression in antennae, but only DabiOBP4 exhibited specific expression in sex pheromone glands, suggesting that they may play many physiological roles in D. abietella. We put forth a reasonable hypothesis about type I pheromone biosynthesis pathways based on these genes identified in the D. abietella sex pheromone gland transcriptome. Our findings lay a foundation for population monitoring, mating disruption, mass trapping, and the development of ecologically acceptable management strategies.

Semiochemicals containing lepidopteran sex pheromones: Wonderland for a natural product chemist

Since the first identification of bombykol, sex pheromones of about 700 moth species have been elucidated. Additionally, field evaluations of synthetic pheromones and their related compounds have revealed the male attraction of another 1,300 species. These pheromones and attractants are listed on the web-sites, "Pheromone Database, Part I." Pheromone components are classified according to their chemical structures into two major groups (Types I and II) and miscellaneous. Based on our previous review published in 2004, studies reported during the last two decades are highlighted here to provide information on the structure characteristics of newly identified pheromones, current techniques for structure determination, new enantioselective syntheses of methyl-branched pheromones, and the progress of biosynthetic research. Besides the moth sex pheromones, various pheromones and allomones from many arthropod species have been uncovered. These semiochemicals are being collected in the "Pheromone Database, Part II." The chemical diversity provides a wonderland for natural product chemists.

A major locus controls a biologically active pheromone component in Heliconius melpomene

Understanding the production, response, and genetics of signals used in mate choice can inform our understanding of the evolution of both intraspecific mate choice and reproductive isolation. Sex pheromones are important for courtship and mate choice in many insects, but we know relatively little of their role in butterflies. The butterfly Heliconius melpomene uses a complex blend of wing androconial compounds during courtship. Electroantennography in H. melpomene and its close relative Heliconius cydno showed that responses to androconial extracts were not species specific. Females of both species responded equally strongly to extracts of both species, suggesting conservation of peripheral nervous system elements across the two species. Individual blend components provoked little to no response, with the exception of octadecanal, a major component of the H. melpomene blend. Supplementing octadecanal on the wings of octadecanal-rich H. melpomene males led to an increase in the time until mating, demonstrating the bioactivity of octadecanal in Heliconius. Using quantitative trait locus (QTL) mapping, we identified a single locus on chromosome 20 responsible for 41% of the parental species' difference in octadecanal production. This QTL does not overlap with any of the major wing color or mate choice loci, nor does it overlap with known regions of elevated or reduced FST . A set of 16 candidate fatty acid biosynthesis genes lies underneath the QTL. Pheromones in Heliconius carry information relevant for mate choice and are under simple genetic control, suggesting they could be important during speciation.

Molecular Characterization and Key Binding Sites of Sex Pheromone-Binding Proteins from the Meadow Moth, Loxostege sticticalis

The meadow moth, Loxostege sticticalis, is a typical agricultural pest that uses sex pheromones to mediate mating behavior; however, the mechanism underlying the selectivity of its pheromone-binding proteins (PBPs) remains unknown. In this study, LstiPBP1 and LstiPBP3 were cloned, expressed, and purified, and the fluorescence binding assay showed that LstiPBP1 binds to the major sex pheromone component, E-11-tetradecenol (E11-14:OH), with high affinity; moreover, E11-14:OH could evoke a significant antennal electrophysiological response and attract L. sticticalis males. After LstiPBP1 was silenced, both the antennal response and attractiveness of E11-14:OH decreased significantly. Molecular docking predicted that a hydrogen bonding site, Leu37, played key role in the binding of LstiPBP1 to E11-14:OH. After Leu37 was mutated, the E11-14:OH-binding affinity decreased drastically. These results suggest that LstiPBP1 participates in E11-14:OH recognition and could be used as a target gene to disturb the mating behavior of L. sticticalis and develop new odorants for pest control.

Two Sympatric Spodoptera Species Could Mutually Recognize Sex Pheromone Components for Behavioral Isolation

Spodoptera exigua and S. litura are two sympatric species in China and many other countries. Both moths employ a multiple component sex pheromone blend, including a common component Z9,E12-14:OAc, and two specific components Z9-14:OH and Z11-16:OAc for S. exigua, and one specific component Z9,E11-14:OAc for S. litura. For the two species, it has been well documented that males are able to recognize and behaviorally attracted by their species-specific sex pheromone, which functions as a means of reproductive isolation, but whether males could mutually recognize pheromone components of its sympatric species is unknown. In the present study, the electroantennogram (EAG) and field evaluation were conducted to address this topic. The EAG recordings revealed that males of each species could significantly respond to specific components of its sympatric species, although the response values were lower than that to its own major component. In field tests, the specific components Z9-14:OH and Z11-16:OAc of S. exigua strongly inhibited the male catches of S. litura to its conspecific sex pheromone, while specific component Z9,E11-14:OAc of S. litura significantly reduced the male catches of S. exigua to its sex pheromone. Furthermore, the combined lure of the two species completely inhibited male catches of S. litura, and significantly decreased the male catches of S. exigua, compared to the species-specific lure alone. The results demonstrated that males of the two sibling species could perceive the specific components of its counterpart, suggesting that mutual recognition of pheromone components may function to strengthen the behavioral isolation between the two species. Our study has added new knowledge to the reproductive isolation via sex pheromone communication system in sympatric moth species, and provided a base for designing of mating disruption tactics targeting multispecies by using insect sex pheromones.

CYPs in different families are involved in the divergent regio-specific epoxidation of alkenyl sex pheromone precursors in moths

In moth species that utilize alkenyl sex pheromones, the epoxidation of alkenes confers further diversity on the chemical structures of pheromone components. Hc_epo1 (CYP341B14), the first pheromone gland (PG)-specific epoxidase identified from the fall webworm Hyphantria cunea (Erebidae), specifically epoxidizes the Z9 double bond in the triene precursor, (3Z,6Z,9Z)-3,6,9-henicosatriene (Z3,Z6,Z9-21:H). In the present study, we identified a novel PG-specific epoxidase, As_epo1, from the Japanese giant looper Ascotis selenaria (Geometridae), which secretes cis-3,4-epoxy-(6Z,9Z)-6,9-nonadecadiene (epo3,Z6,Z9-19:H) as the main sex pheromone component. A functional assay using the Sf9 insect cell line-baculovirus expression system showed that As_epo1 specifically epoxidizes the Z3 double bond in the pheromone precursor triene, (3Z,6Z,9Z)-3,6,9-nonadecatriene (Z3,Z6,Z9-19:H). As_epo1 also Z3-specifically epoxidized a triene with a longer carbon chain, Z3,Z6,Z9-21:H, which does not occur in this species. A phylogenetic analysis indicated that As_epo1 belonged to the CYP340 family, not the CYP341 family to which Hc_epo1 belongs. These results suggest that moth PG-specific epoxidases with divergent regio-specificities have evolved independently.

Functional characterization of the epoxidase gene, Li_epo1 (CYP341B14), involved in generation of epoxyalkene pheromones in the mulberry tiger moth Lemyra imparilis

Epoxidation of alkenes derived from essential fatty acids is a key step in the biosynthesis of sex pheromones in moth species that utilize alkenyl sex pheromones. The position of the epoxy ring in the pheromone molecule differs depending on the species, thereby conferring diversities on sex pheromones. To date, only one pheromone gland (PG)-specific epoxidase, Hc_epo1 (CYP341B14), has been reported. Hc_epo1, which was identified from an arctiid moth Hyphantria cunea, catalyzes the epoxidation of a double bond at position 9 of the triene, Z3,Z6,Z9-21:H. In the present study, we investigated the PG-specific epoxidase from another arctiid, the mulberry tiger moth Lemyra imparilis, in order to verify whether cytochrome P450 in the CYP341B subfamily, to which Hc_epo1 belongs to, is responsible for the epoxidation of pheromone precursors at position 9 in moths other than H. cunea. A fragment of the Hc_epo1 homolog was amplified from cDNA prepared from the PG of L. imparilis by PCR with degenerate primers. The deduced amino acid sequence of the subsequently cloned homolog, Li_epo1, showed 88.5% identity to Hc_epo1. A functional assay using the Sf9 insect cell line-baculovirus expression system showed that Li_epo1 exhibited epoxidase activity with high selectivity to the double bond at position 9 of two trienes, Z3,Z6,Z9-21:H and Z3,Z6,Z9-23:H, precursors of epoxy diene sex pheromone components in L. imparilis.

Identification of Sex Pheromone of Miltochrista striata (Lepidoptera: Arctiidae)

A species of lichen moth, Miltochrista striata (Bremer & Grey, 1852), feeds on lichens in Chinese tea plantations (Camellia sinensis (L.) O. Kuntze (Ericales:Theaceae)). A previous sex attractant screening test showed that male moths of M. striata were attracted by a mixture of (Z,Z,Z)-3,6,9-octadecatriene (Z3,Z6,Z9-18:H), (Z,Z,Z)-3,6,9-nonadecatriene (Z3,Z6,Z9-19:H), and their monoepoxy derivatives. To determine which of the component is an effective sex attractant for M. striata, the sex pheromone glands of female moths were excised and extracted with n-hexane. By comparison with the retention time and mass spectra of synthetic chemicals, two compounds in the crude extracts were identified as Z3,Z6,Z9-18:H and (Z,Z)-3,6-cis-9,10-epoxy-octadecadiene (Z3,Z6,epo9-18:H) using gas chromatography-mass spectrometry. The results of electroantennographic tests showed that the electrophysiological activities of Z3,Z6,Z9-18:H and Z3,Z6,epo9-18:H were distinctly higher than those of (Z,Z)-6,9-cis-3,4-epoxy-octadecadiene, (Z,Z)-3,9-cis-6,7-epoxy-octadecadiene, (Z,Z,Z)-3,6,9-nonadecatriene, (Z,Z)-6,9-cis-3,4-epoxy-nonadecatriene, (Z,Z)-3,9-cis-6,7-epoxy-nonadecatriene, and (Z,Z)-3,6-cis-9,10-epoxy-nonadecatriene. Field trapping showed that only a mixture of Z3,Z6,Z9-18:H and Z3,Z6,epo9-18:H attracted male moths, and the optimal mixture of these compounds was the ratio of 4:6 at 1.0-mg dosage. The results represent the first determination of the sex pheromone of a lichen moth in a tea plantation and provide a scientific basis to develop an effective protocol using sex pheromone to monitor populations of M. striata.

Physicochemical Basis and Comparison of Two Type II Sex Pheromone Components Binding with Pheromone-Binding Protein 2 from Tea Geometrid, Ectropis obliqua

Lepidopteran geometrid moth can produce complex Type II sex pheromone components to attract males and trigger mating behavior. Although several sex pheromone components have been identified, it remains unclear whether their physicochemical roles in sex pheromone sensing are the same. Therefore, we utilized tea geometrid ( Ectropis obliqua) as an example model to investigate and compare the physicochemical basis of two key Type II sex pheromone components, cis-6,7-epoxy-(3Z,9Z)-3,9-octadecadiene ( Z3 Z9-6,7-epo-18:Hy) and ( Z, Z, Z)-3,6,9-octadecatriene (Z3Z6Z9-18:Hy), interacting with pheromone-binding protein 2 ( EoblPBP2) from E. obliqua. Multispectral, thermodynamic, docking, and site-directed mutagenesis indicated that the major sex pheromone component Z3Z9-6,7-epo-18:Hy is more susceptible to pH-tuned than the minor component Z3Z6Z9-18:Hy, whereas Z3Z6Z9-18:Hy seems to be more susceptible to temperature and amino acid mutations than Z3Z9-6,7-epo-18:Hy. Our study suggests that different components of Type II sex pheromone play different binding characters under specific conditions in the physicochemical behavior. This deeply supplements the theoretical knowledge of Type II pheromones involved in the recognition and discrimination in the Lepidopteran sex pheromones family.

Identification and Field Evaluation of the Sex Pheromone of Orthaga achatina (Lepidoptera: Pyralidae)

Orthaga achatina (Lepidoptera: Pyralidae) is the most serious pest in south China of camphor trees, Cinnamomum camphora (L.) Presl, an important urban tree species. Gas chromatography-electroantennographic detection (GC-EAD) of the sex pheromone of O. achatina showed three EAD-active components. Coupled gas chromatography/mass spectrometry analyses identified these as (Z)-11-hexadecenol (Z11-16:OH), (Z)-11-hexadecenyl acetate (Z11-16:OAc), and (3Z,6Z,9Z,12Z,15Z)-tricosapentaene (Z3,Z6,Z9,Z12,Z15-23:H). In field tests using different combinations of the three compounds, male moths were attracted to a mixture of Z11-16:OAc and Z3,Z6,Z9,Z12,Z15-23:H, but less attracted to other blends. Further field tests with different ratios of the two compounds determined the optimal ratio of the binary blend as 500:250. The addition of Z11-16:OH to Z11-16:OAc, or to the binary mixture of Z11-16: OAc and the pentaene did not yield higher catches. This shows that O. achatina uses a mixture of Type I and Type II sex pheromone components. Orthaga achatina is the third Pyraloidea species found to utilize Z3,Z6,Z9,Z12,Z15-23:H as a sex pheromone component.

Unsaturated Cuticular Hydrocarbon Components of the Sex Pheromone of Eggplant Fruit Borer, Leucinodes orbonalis Guenée (Lepidoptera: Crambidae)

Leucinodes orbonalis is one of the most damaging insect pests affecting eggplant in the Mekong Delta of Vietnam. While (E)-11-hexadecenyl acetate (E11-16:OAc) and its alcohol, (E)-11-hexadecenol (E11-16:OH), have been identified as major and minor sex pheromone components, respectively, few males were attracted to a blend of these compounds in Vietnamese fields. In order to utilize synthetic pheromone of L. orbonalis as a tool for sustainable pest management programs, we reexamined the pheromone of this species in order to search for other minor components. Gas chromatography-electroantennogram detection and gas chromatography/mass spectrometry analyses of abdominal tip extract revealed the presence of two electroantennogram-active compounds, E11-16:OAc and (3Z,6Z,9Z)-3,6,9-tricosatriene (Z3,Z6,Z9-23:H) in a ratio of 100:2. An extract of the abdomen and thorax showed an additional electroantennogram-active component, (3Z,6Z,9Z)-3,6,9-docosatriene (Z3,Z6,Z9-22:H), with the three compounds (E11-16:OAc, Z3,Z6,Z9-23:H and Z3,Z6,Z9-22:H) being present in a ratio of 100:45:1, indicating that the trienes were mainly present on the cuticular surface. In the field, traps baited with E11-16:OAc and the C₂₃ triene, in a mix of 10:1, caught more male moths than traps baited with the acetate alone. A field evaluation of other polyunsaturated hydrocarbons showed that the C₂₂ triene found in body extract also increased catches when added to the acetate, but no other hydrocarbons did. In contrast, to other studies with this moth, the addition of E11-16:OH to E11-16:OAc plus the C₂₂ or C₂₃ triene, resulted in decreased trap catches.

Identification of the Female-Produced Sex Pheromone of an Invasive Greenhouse Pest, the European Pepper Moth (Duponchelia fovealis)

The European pepper moth (Duponchelia fovealis, Lepidoptera, Crambidae, Spilomelinae) is an invasive pest of greenhouses in many countries, causing serious damages to horticultural plants. Coupled gas chromatographic-electroantennographic detection analysis of the female gland extract revealed two antennally active peaks. Using coupled gas chromatography-mass spectrometry (GC-MS), one was identified as (Z)-11-hexadecenal (Z11-16:Ald); however, further analysis on different types of capillary columns indicated that the second active compound has two different isomers, (E)-13-octadecenal (E13-18:Ald) and (Z)-13-octadecenal (Z13-18:Ald). The approximate ratio of E13-18:Ald, Z13-18:Ald and Z11-16:Ald in the crude pheromone gland extract was 10:1:0.1, respectively. Single sensillum recordings showed that there was one sensory neuron that responded with a high amplitude spike to both E13-18:Ald and Z13-18:Ald, while another neuron housed in the same sensillum responded to Z11-16:Ald. Field evaluation of the identified compounds indicated that the E13-18:Ald was necessary to evoke the attraction of males; although the presence of Z13-18:Ald and Z11-16:Ald increased the catches in traps. The highest number of caught males was achieved when E13-18:Ald, Z13-18:Ald and Z11-16:Ald were present in baits in the same ratio as in the female gland extract. This pheromone can be used in a monitoring strategy and could potentially lead to the development of mating disruption.

Production, identification, and field evaluation of sex pheromone from calling females in Diaphania angustalis (Lepidoptera: Crambidae)

Insect sex pheromones play a crucial role in the mate finding and calling behavior of Lepidoptera pests. Currently, little is known about the chemical ecology of Diaphania angustalis Snellen (Lepidoptera: Crambidae), a severe and important defoliator attacking the medicinal plant, Alstonia scholaris. In the present study, the pheromone components of D. angustalis females were investigated using electrophysiological and behavioral methods. Distilled hexane extracts of female pheromone glands were analyzed through electroantennogram (EAG) and gas chromatography-electroantennogram detector (GC-EAD), and the active compounds were identified through gas chromatography-mass spectrometry (GC-MS). Production peak of female sex pheromone occurred on the third day of age at 5 h into the scotophase with the EAG test, and the hexane extracts were attractive to males in the wind tunnel test. GC-EAD analysis of virgin males to gland extracts that were subsequently evaluated showed two active compounds, (E,E)-10,12-hexadecadienal (E10E12-16:Ald) and (E,E)-10,12-hexadecadien-1-ol (E10E12-16:OH), based on comparison of retention time and mass spectrum, with suitable synthetic compounds. Under laboratory conditions, the blend of E10E12-16:Ald and E10E12-16:OH in a ratio of 9:1 elicited a stronger EAG response than other treatments or a single component. In the field, more male moths were captured by traps baited with the mixture of E10E2-16:Ald and E10E2-16:OH in a ratio of 9:1, whereas a mixture of 8:1 and 10:1 also caught males. Accordingly, E10E2-16:Ald and E10E2-16:OH were regarded as the major sex pheromone components in D. angustalis females.

Identification of in situ flower volatiles from kiwifruit (Actinidia chinensis var. deliciosa) cultivars and their male pollenisers in a New Zealand orchard

In situ flower volatiles from six kiwifruit cultivars (Actinidia chinensis var. deliciosa); 'Hayward', 'Chieftain', 'M56', 'Zes007' (Green11), 'M36', and 'M43' were collected by dynamic headspace sampling. Forty-five compounds were detected in the headspace of the flowers, with straight chain hydrocarbons and terpenes accounting for >98% of the volatiles emitted quantitatively across the six cultivars. Of these hydrocarbons, (3Z,6Z,9Z)-heptadecatriene is reported for the first time from a floral source while (8Z)-hexadecene and (9Z)-nonadecene are reported for the first time from kiwifruit flowers. All three hydrocarbons were verified by synthesis. Quantitative comparison of the six honey bee perceived compounds from the headspace of the cultivars showed that the males 'M36' and 'M43' closely matched the female cultivar Green11 that they are used to pollinate. Males 'M56' and 'Chieftain' were not as closely matched to the female cultivar 'Hayward' that they are used to pollinate. The male 'M56' in particular differed significantly from the female 'Hayward' in four of the six honey bee perceived compounds.

Molecular and functional characterization of a candidate sex pheromone receptor OR1 in Spodoptera litura

Olfaction is primarily mediated by highly specified olfactory receptors (ORs). Here, we cloned and identified an olfactory receptor, named SlituOR1 (Genbank no. JN835269), from Spodoptera litura and found evidence that it is a candidate pheromone receptor. It exhibited male-biased expression in the antennae, where it was localized at the base of sensilla trichoidea, the antennal sensilla mainly responsive to pheromones in moths. Conserved orthologues of this receptor, found among known pheromone receptors within the Lepidoptera, and SlituOR1 were placed among a clade of candidate pheromone receptors in a phylogeny tree of insect OR gene sequences. SlituOR1 showed differential expression in S. litura populations attracted to traps baited with different ratios of the two sex pheromone components (9Z,11E)-tetradecadienyl acetate (Z9E11-14:OAc) and (9Z,12E)-tetradecadienyl acetate (Z9E12-14:OAc). Knocking down of SlituOR1 by RNA interference reduced the electroantennogram (EAG) response to Z9E11-14:OAc, and this result is consistent with the field trapping experiment. We infer that variation in transcription levels of olfactory receptors may modulate sex pheromone perception in male moths and could provide some of the flexibility required to maintain the functionality of communication with females when a population is adapting to a new niche and reproductive isolation becomes an advantage.

Molecular identification of differential expression genes associated with sex pheromone biosynthesis in Spodoptera exigua

Species-specific sex pheromone is biosynthesized and released in most female moths as a chemical cue in mating communication. However, information on genes involved in this pathway is limited. The beet armyworm, Spodoptera exigua, is a cosmopolitan agricultural pest that causes severe economic losses to many crops. In China, the female sex pheromones in sex pheromone glands (PGs) of S. exigua have been measured which comprises (Z,E)-9,12-tetradecadienyl acetate, (Z)-9-tetradecen-l-ol, (Z)-9-tetradecenyl acetate, and (Z,E)-9,12-tetradecadien-1-ol in a ratio of 47:18:18:17. Fifty-nine putative genes related to sex pheromone biosynthesis were identified in the present study by sequencing and analyzing the sex pheromone gland (PG) transcriptome of S. exigua. Expression profiles revealed that two desaturase (SexiDes5 and SexiDes11) and three fatty acyl reductase (SexiFAR2, 3, and 9) genes had PG-specific expression, and phylogenetic analysis demonstrated that they clustered with genes known to be involved in pheromone synthesis in other moth species. Our results provide crucial background information that could facilitate the elucidation of sex pheromone biosynthesis pathway of S. exigua as well as other Spodoptera species and help identify potential targets for disrupting sexual communication in S. exigua for developing novel environment-friendly pesticides.

Identification, synthesis and mass spectrometry of a macrolide from the African reed frog Hyperolius cinnamomeoventris

The contents of the gular glands of the male African reed frog Hyperolius cinnamomeoventris consist of a mixture of aliphatic macrolides and sesquiterpenes. While the known macrolide gephyromantolide A was readily identified, the structure of another major component was suggested to be a tetradecen-13-olide. The synthesis of the two candidate compounds (Z)-5- and (Z)-9-tetradecen-13-olide revealed the former to be the naturally occurring compound. The synthesis used ring-closing metathesis as key step. While the Hoveyda–Grubbs catalyst furnished a broad range of isomeric products, the (Z)-selective Grubbs catalyst lead to pure (Z)-products. Analysis by chiral GC revealed the natural frog compound to be (5Z,13S)-5-tetradecen-13-olide (1). This compound is also present in the secretion of other hyperoliid frogs as well as in femoral glands of male mantellid frogs such as Spinomantis aglavei. The mass spectra of the synthesized macrolides as well as their rearranged isomers obtained during ring-closing metathesis showed that it is possible to assign the location of the double bond in an unsaturated macrolide on the basis of its EI mass spectrum. The occurrence of characteristic ions can be explained by the fragmentation pathway proposed in the article. In contrast, the localization of a double bond in many aliphatic open-chain compounds like alkenes, alcohols or acetates, important structural classes of pheromones, is usually not possible from an EI mass spectrum. In the article, we present the synthesis and for the first time elucidate the structure of macrolides from the frog family Hyperoliidae.

Will climate change affect insect pheromonal communication?

Understanding how climate change will affect species interactions is a challenge for all branches of ecology. We have only limited understanding of how increasing temperature and atmospheric CO₂ and O₃ levels will affect pheromone-mediated communication among insects. Based on the existing literature, we suggest that the entire process of pheromonal communication, from production to behavioural response, is likely to be impacted by increases in temperature and modifications to atmospheric CO₂ and O₃ levels. We argue that insect species relying on long-range chemical signals will be most impacted, because these signals will likely suffer from longer exposure to oxidative gases during dispersal. We provide future directions for research programmes investigating the consequences of climate change on insect pheromonal communication.

Single-Component Pheromone Consisting of Bombykal in a Diurnal Hawk Moth, Neogurelca himachala sangaica

Recent work has suggested that hawk moths share pheromone components but are sexually separated by qualitative and quantitative differences in their pheromone blends. During field assays on the sex pheromones of other species, a diurnal hawk moth, Neogurelca himachala sangaica (Lepidoptera: Sphingidae), was frequently captured, but the composition of the sex pheromone of this species was not known. Analysis of hexane extracts of the pheromone glands of calling female by gas chromatography (GC) using an electroantennographic detector (EAD) revealed two components that elicited EAD responses from male moth antennae. These components were identified by their mass spectra and retention indices on two GC columns as (10E,12Z)-10,12-hexadecadienal (E10,Z12-16:Ald) and a trace of its (10E,12E)-isomer (E10,E12-16:Ald) in 98:2 ratio. In field experiments, E10,Z12-16:Ald alone attracted male moths, and addition of E10,E12-16:Ald significantly reduced the attractiveness, even at the naturally-occurring ratio. Analysis of the data using a generalized linear mixed model showed that E10,Z12-16:Ald positively contributed to attractiveness, whereas E10,E12-16:Ald did so negatively, and it was concluded that the sex pheromone of N. himachala sangaica consists solely of E10,Z12-16:Ald, bombykal. The negative effect of E10,E12-16:Ald on attractiveness could promote the species-specificity of this single-component pheromone system.

Analysis of Tea Geometrid (Ectropis grisescens) Pheromone Gland Extracts Using GC-EAD and GC×GC/TOFMS

The tea geometrid, Ectropis grisescens Warren, is one of the most severe defoliator insect pests in tea plantations, China. The use of insecticides, etc., is forbidden on organic tea plantations. No female-produced sex pheromones of E. grisescens had been previously identified. In the present study, female gland extracts were analyzed by gas chromatography coupled with electroantennographic detection (GC-EAD) and two-dimensional gas chromatography (GC×GC) using a time-of-flight mass spectrometric detector (TOFMS). Two components, (Z,Z,Z)-3,6,9-octadecatriene (Z3Z6Z9-18:Hy) and (Z,Z)-3,9-6,7-epoxyoctadecadiene (Z3Z9-6,7-epo-18:Hy), were identified from pheromone gland extracts, and their electrophysiological and behavioral activity evaluated. Under laboratory conditions, Z3Z9-6,7-epo-18:Hy elicited a stronger electrophysiological response than Z3Z6Z9-18:Hy. In the field, traps baited with Z3Z9-6,7-epo-18:Hy alone showed better results than traps baited with Z3Z6Z9-18:Hy, and the binary mixture of Z3Z9-6,7-epo-18:Hy and Z3Z6Z9-18:Hy in a ratio of 4:1 (approximate ratio of females emitting pheromone) caught more males than the single components or any other blends. This study showed that Z3Z6Z9-18:Hy and Z3Z9-6,7-epo-18:Hy are the sex pheromone components of E. grisescens and that they prove useful in developing alternative management tools for the pest.

Long Chain Alcohols Produced by Trichoderma citrinoviride Have Phagodeterrent Activity against the Bird Cherry-Oat Aphid Rhopalosiphum padi

In this study we report the effects of fungal metabolites isolated from cultures of the fungus Trichoderma citrinoviride ITEM 4484 on the feeding preference of the aphid Rhopalosiphum padi, a major pest of cereal crops. Different phagodeterrent metabolites were purified by a combination of direct and reverse phase column chromatography and thin-layer chromatography. Chemical investigations, by spectroscopic and chemical methods, led to the identification of different long chain primary alcohols (LCOHs) of the general formula R-OH, wherein R is a long, unbranched, unsubstituted, linear aliphatic group. LCOHs have been reported as components of lepidopteran pheromone blends, but their phagodeterrent effect to aphids is herein reported for the first time. The effects of LCOHs on R. padi were studied by behavioral and electrophysiological bioassays. Feeding preference tests that were carried out with winged and wingless morphs of R. padi showed that LCOHs had high phagodeterrent activity and restrained aphids from settling on treated leaves at a concentration as low as 0.15 mM (0.036 g/l). The results of different electrophysiological analyses indicated that taste receptor neurons located on the aphid tarsomeres were involved in the LCOHs perception. Behavioral assays carried out with some commercial agrochemicals, including azadirachtin A, pyrethrum and a mineral oil-based product, in combination with 1-hexadecanol, the LCOH most abundantly produced by T. citrinoviride ITEM 4484, showed that these different active principles could be applied together, resulting in a useful increase of the phagodeterrent effect. The data shown indicate that these compounds can be profitably utilized for novel applications in biotechnical control of aphid pests. Furthermore, the tested LCOHs have no chiral centers and therefore can be obtained with good yield and at low cost through chemical synthesis, as well as from natural sources.

Electrophysiological and behavioral responses of Diaphania glauculalis males to female sex pheromone

The aim of this study is to identify the pheromone active component of female moths, Diaphania glauculalis, an important pest of Anthocephalus chinensis in China. The sex pheromone was extracted from sex pheromone gland extracts of virgin female moth of D. glauculalis using n-hexane, and the pheromone gland extracts of females were analyzed using coupled gas chromatography-electroantennogram detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). The sex pheromone active components were based on the comparison the retention time and mass spectrum, with suitable synthetic compounds. (E)-11-hexadecenal (E11-16:Ald) and (E,E)-10,12-hexadecadienal (E10E12-16:Ald) were identified as the major sex pheromone components in the females. Their biological activities were evaluated in a series of electroantennogram (EAG) experiments and four-arm olfactometer assays using synthetic compounds. D. glauculalis males could be attracted by any single component, but a mixture of the E11-16:Ald and E10E12-16:Ald in a ratio of 5:5 elicited a substantial response, demonstrating that the binary blend is essential in male attraction. We therefore conclude that the aldehyde compounds, a mixture of E11-16:Ald and E10E12-16:Ald, comprise the sex pheromone components of D. glauculalis, which might be applied for insect field trapping.

Chiral methyl-branched pheromones

Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.

(Z)-13-Hexadecenyl Acetate: a Novel Moth Sex Pheromone Component from Herpetogramma submarginale (Lepidoptera: Crambidae)

The sex pheromone of Herpetogramma submarginale (Swinhoe) was studied by gas chromatography (GC) with electroantennographic detection and GC coupled with mass spectrometry. Two pheromone candidates detected in the gland extracts of females were identified as (Z)-13-hexadecenyl acetate (Z13-16:OAc) and (E)-13-hexadecenyl acetate (E13-16:OAc) in a ratio of 87:13 by mass spectral analysis of the natural pheromone components and their dimethyldisulfide adducts. In field tests, Z13-16:OAc alone attracted H. submarginale males and caught significantly more males than live virgin females. Addition of E13-16:OAc did not enhance the attractiveness of Z13-16:OAc. Derivatives of Z13-16:OAc also were tested as potential pheromone components. Addition of (Z)-13-hexadecen-1-ol significantly reduced the number of males captured, and (Z)-13-hexadecenal had no effect on the attractiveness of the lure. These results suggest that the female-produced sex pheromone of H. submarginale is Z13-16:OAc. This hexadecenyl acetate is a novel moth sex pheromone component.

Female sex pheromones of two Japanese saturniid species, Rhodinia fugax and Loepa sakaei: identification, synthesis, and field evaluation

While 11 species in the family Saturniidae are found in Japan, no sex pheromones of the native species had been investigated previously. We collected larvae of Rhodinia fugax in Nagano and Tottori Prefecture, and of Loepa sakaei in Okinawa Prefecture, and extracted sex pheromones of these two species from virgin female moths. In gas chromatography-electroantennogram detection (GC-EAD) analyses, male antennae of each species responded to one component in the respective pheromone extracts of conspecific females. Chemical analyses of the extracts by GC/mass spectrometry revealed that the EAD-active compounds of R. fugax and L. sakaei were a hexadecadienal and a tetradecadienyl acetate, respectively. The two species belong to the subfamily Saturniinae, and the mass spectra of both were similar to that of the 6,11-hexadecadienyl acetate identified from Antheraea polyphemus, classified in the same subfamily, suggesting the same 6,11-dienyl structure for the C16 aldehyde and a 4,9-dienyl structure for the C14 acetate. Based on this assumption, four geometrical isomers of each dienyl compound were stereoselectively synthesized via acetylene intermediates, compared to the natural products, and tested in the field. Male catches confirmed the pheromone structures of the two Japanese saturniid species as (6E,11Z)-6,11-hexadecadienal for R. fugax and (4E,9Z)-4,9-tetradecadienyl acetate for L. sakaei. The compounds have a characteristic 1,6-dienyl motif common to the pheromones of Saturniinae species.

Identification of the sex pheromone of the diurnal hawk moth, Hemaris affinis

Sex pheromones of nocturnal hawk moths have been identified previously, but not those of diurnal hawk moths. Here, we report laboratory analyses and field testing of the sex pheromone of the diurnal hawk moth, Hemaris affinis (Bremer 1861) (Lepidoptera: Sphingidae). Sex pheromone glands were removed and extracted in hexane during peak calling activity of virgin female moths. Analysis of gland extracts by gas chromatography (GC) with electroantennographic detection revealed three components that elicited responses from male moth antennae. These components were identified, based on their mass spectra and retention indices on two GC columns, as (Z)-11-hexadecenal and (10E, 12Z)- and (10E,12E)-10,12-hexadecadienals with a ratio of 45:20:35. In a field experiment, traps baited with the three-component synthetic blend, but none of the single- or two-component blends, caught male moths. All three pheromone components have been identified previously in pheromones of other Lepidoptera, including Sphingid moths, and thus the ternary blend is probably responsible for the species specificity of the pheromone of this moth.

CYP341B14: a cytochrome P450 involved in the specific epoxidation of pheromone precursors in the fall webworm Hyphantria cunea

Two of the four sex pheromone components in the fall webworm Hyphantria cunea (Lepidoptera: Arctiidae), cis-9,10-epoxy-(3Z,6Z)-3,6-henicosadiene and cis-9,10-epoxy-(3Z,6Z)-1,3,6-henicosatriene, possess an epoxy ring within their molecules. These compounds have been suggested to be biosynthesized from dietary linolenic acid via the following enzymatic reactions; chain elongation, terminal desaturation (in the case of the latter component), decarboxylation, and epoxidation. The last step of this biosynthesis, epoxidation, is known to occur specifically in the sex pheromone gland of females. We identified the enzyme involved in the epoxidation of pheromone precursors by focusing on cytochromes P450, which are known to catalyze the oxidation of various compounds. Three P450-like sequences (Hc_epo1, Hc_epo2, and Hc_epo3) were identified in the cDNA library prepared from the sex pheromone gland of H. cunea. Among these clones, only Hc_epo1 was specifically expressed in the pheromone gland. The full-length sequence of Hc_epo1 contained an ORF of 1527 bp, which encoded a protein of 509 amino acids with a predicted molecular weight of 57.9 kDa. The deduced Hc_epo1 amino acid sequence possessed the characteristics of P450. A phylogenetic analysis of the sequence indicated that Hc_epo1 belonged to the CYP341B clade in the CYP341 family. Therefore, it was named CYP341B14. A subsequent functional assay using Sf-9 cells transiently expressing CYP341B14 demonstrated that this P450 protein was able to specifically epoxidize a (Z)-double bond at the 9th position in the pheromone precursor, (3Z,6Z,9Z)-3,6,9-henicosatriene.

Molecular evolution of the odorant and gustatory receptor genes in lepidopteran insects: implications for their adaptation and speciation

Lepidoptera (comprised of butterflies and moths) is one of the largest groups of insects, including more than 160,000 described species. Chemoreception plays important roles in the adaptation of these species to a wide range of niches, e.g., plant hosts, egg-laying sites, and mates. This study investigated the molecular evolution of the lepidopteran odorant (Or) and gustatory receptor (Gr) genes using recently identified genes from Bombyx mori, Danaus plexippus, Heliconius melpomene, Plutella xylostella, Heliothis virescens, Manduca sexta, Cydia pomonella, and Spodoptera littoralis. A limited number of cases of large lineage-specific gene expansion are observed (except in the P. xylostella lineage), possibly due to selection against tandem gene duplication. There has been strong purifying selection during the evolution of both lepidopteran odorant and gustatory genes, as shown by the low ω values estimated through CodeML analysis, ranging from 0.0093 to 0.3926. However, purifying selection has been relaxed on some amino acid sites in these receptors, leading to sequence divergence, which is a precursor of positive selection on these sequences. Signatures of positive selection were detected only in a few loci from the lineage-specific analysis. Estimation of gene gains and losses suggests that the common ancestor of the Lepidoptera had fewer Or genes compared to extant species and an even more reduced number of Gr genes, particularly within the bitter receptor clade. Multiple gene gains and a few gene losses occurred during the evolution of Lepidoptera. Gene family expansion may be associated with the adaptation of lepidopteran species to plant hosts, especially after angiosperm radiation. Phylogenetic analysis of the moth sex pheromone receptor genes suggested that chromosomal translocations have occurred several times. New sex pheromone receptors have arisen through tandem gene duplication. Positive selection was detected at some amino acid sites predicted to be in the extracellular and transmembrane regions of the newly duplicated genes, which might be associated with the evolution of the new pheromone receptors.

Reexamination of the female sex pheromone of the sweet potato vine borer moth: identification and field evaluation of a tricosatriene

The sweet potato vine borer moth, Omphisa anastomosalis (Pyraloidea: Crambidae), is a serious pest in tropical and subtropical Asia-Pacific regions. In previous work using a population from Okinawa, Japan, (10E,14E)-10,14-hexadecadienal (E10,E14-16:Ald) was identified as the major pheromone component, with hexadecanal, (E)-10-hexadecenal, and (E)-14-hexadecenal as minor components. However, traps baited with the synthetic compounds were less effective at attracting males in the field than those baited with virgin females. While Pyraloidea females usually produce only Type I pheromone components (unsaturated fatty alcohols and their derivatives), the pheromones of some Pyraloidea species have been shown to involve a combination of both Type I and Type II components (unsaturated hydrocarbons and their epoxides). We examined an extract of the pheromone glands of female O. anastomosalis from Vietnam by gas chromatography coupled to mass spectrometry and detected (3Z,6Z,9Z)-3,6,9-tricosatriene (Z3,Z6,Z9-23:H) in addition to the compounds identified previously. All four isomers of 10,14-16:Ald were synthesized. A mixture of synthetic E10,E14-16:Ald and Z3,Z6,Z9-23:H in a ratio of 1:0.2-1:2 was attractive to male moths in Vietnam, indicating the strong synergistic effect of the Type II compound. Addition of the other minor pheromone components to the binary blend did not increase the number of male moths captured. Combinations of Z3,Z6,Z9-23:H with the other three geometrical isomers of E10,E14-16:Ald attracted no males, further substantiating the 10E,14E configuration of the natural diene component. E10,E14-16:Ald mixed with other polyunsaturated hydrocarbons showed that mixtures that included a C21 triene, a C22 triene, or a C23 pentaene attracted as many males as did the mixture with Z3,Z6,Z9-23:H. The identification of a highly attractive sex pheromone will help in developing efficient strategies for monitoring and control of O. anastomosalis populations in sweet potato fields.

Female moth pheromones

The sex pheromone, a volatile secreted by a female moth, is stored in the pheromone gland and can be easily extracted with hexane. The extract is effectively analyzed using a gas chromatography combined with an electro-antennogram detector (GC-EAD) and a mass spectrometry (GC-MS), both of which are equipped with a capillary column. GC-EAD analysis indicates the number of pheromone components that have a different chromatographic behavior. The mass spectrum measured by GC-MS suggests the outline of the chemical structure. In addition to a comparison with chemical data of authentic synthetic compounds, micro-chemical reactions reveal a precise structure of the natural pheromone. Finally, the chemical structure is confirmed by field evaluation of the synthetic pheromone.

Synthesis and field evaluation of stereoisomers and analogues of 5-methylheptadecan-7-ol, an unusual sex pheromone component of the lichen moth, Miltochrista calamina

Females of the lichen moth, Miltochrista calamina (Arctiidae, Lithosiinae), were previously shown to produce 5-methylheptadecan-7-ol (1) as a sex pheromone. In field tests, males were attracted only by the (5R,7R)-isomer of the four stereoisomers that were prepared by separation from two mixtures of diastereoisomers. A new route to (5R,7R)-1 starting from (S)-propylene oxide was developed utilizing the SN2 reaction of an optically active secondary tosylate and the Jacobsen hydrolytic kinetic resolution of an epoxide intermediate as key steps. Enantioselective HPLC analysis of the product and the antipode synthesized from (R)-propylene oxide confirmed their high enantiomeric excess (> 99 %). Using this stereospecific synthesis, six analogues with the same configuration as (5R,7R)-1 but with different alkyl chain(s) connected to the stereogenic centers were prepared in order to obtain GC/MS data and to examine the ability of M. calamina males to discriminate between them. The mass spectra of the synthetic analogues revealed characteristic fragment ions derived by cleavage around the methyl group in addition to that at the hydroxyl group. In field trapping tests, five out of the six compounds were attractive to male M. calamina moths, indicating that the males distinguished the configurations of methyl and hydroxyl groups but were less able to perceive differences in the lengths of the two alkyl chains in the pheromone.

Identification of conjugated pentadecadienals as sex pheromone components of the sphingid moth, Dolbina tancrei

Homologs of bombykal, (10E,12Z)-10,12-hexadecadienal, have been reported to be sex pheromones or sexual attractants of several species of sphingid moths. In this study, we identified novel bombykal analogs as sex pheromone components from a Japanese sphingid moth, Dolbina tancrei. Staudinger (Sphingidae: Lepidoptera). Sex pheromone gland extracts from calling female moths were subjected to gas chromatography/electroantennograhic detection (GC/EAD), gas chromatography/mass spectrometry (GC/MS), and gas chromatography (GC) analyses. GC/EAD analyses showed two active components in the crude pheromone extracts. GC/MS analysis determined these two components to be pentadecadienals. GC/MS of their MTAD derivatives showed conjugated double bonds at the 9- and 11-positions, indicating 9,11-pentadecadienals. The isomeric configurations of these candidates were determined by comparison of their Kováts retention indices with those of synthetic compounds. Field bioassays with the four isomers of 9,11-pentadecadienal and their mixtures confirmed that the two sex pheromone components of D. tancrei are (9E,11Z)-9,11-pentadecadienal and (9Z,11Z)-9,11-pentadecadienal, with the highest male catches observed for a 90:10 blend. This is the first report of 9,11-pentadecadienals as sex pheromone components in lepidopteran species.

On-site airborne pheromone sensing

Pheromones and other semiochemicals play an important role in the natural world by influencing the behavior of plants, mammals, and insects. In the latter case, species-dependent pheromone communication has numerous applications, including the detection, trapping, monitoring and guiding of insects, as well as pest management in agriculture. On-site sensors are desirable when volatile organic compounds (VOCs) are used as semiochemicals. Insects have evolved highly selective sensors for such compounds, so biosensors comprising complete insects, isolated organs or individual proteins can be highly effective. However, isolated insect organs have a limited lifetime as biosensor, so biomimetic approaches are needed for prolonged monitoring, novel applications, or measurements in challenging environments. We discuss the development of on-site biosensors and biomimetic approaches for airborne-pheromone sensing, together with biomimetic VOC sensor systems. Furthermore, the infochemical effect describing the anthropogenic contamination of the ecosystem through semiochemicals, will be considered in the context of novel on-site pheromone sensing-systems.

Characterization of posticlure and the structure-related sex pheromone candidates prepared by epoxidation of (6Z,9Z,11E)-6,9,11-trienes and (3Z,6Z,9Z,11E)-3,6,9,11-tetraenes

trans-11,12-Epoxy-(6Z,9Z)-6,9-henicosadiene (posticlure) has been identified from a pheromone gland of the lymantriid species, Orgyia postica. Since the diversity of Lepidoptera suggests that some species utilize the structure-related epoxy compound as a sex pheromone component, epoxydienes and epoxytrienes derived from (6Z,9Z,11E)-6,9,11-trienes and (3Z,6Z,9Z,11E)-3,6,9,11-tetraenes with a C19-C21 chain were systematically synthesized and the chemical data were accumulated in order to contribute to a new pheromone research. Peracid oxidation of each triene and each tetraene produced, respectively, a mixture of three epoxydienes (cis-6,7-epoxy-9,11-diene; cis-9,10-epoxy-6,11-diene; and trans-11,12-epoxy-6,9-diene) and four epoxytrienes (cis-3,4-epoxy-6,9,11-triene; cis-6,7-epoxy-3,9,11-triene; cis-9,10-epoxy-3,6,11-triene; and trans-11,12-epoxy-3,6,9-triene). While the 9,10-epoxy compounds were unstable and, interestingly, converted into 9-ketone derivatives after chromatography over SiO2, each positional isomer was isolated by HPLC equipped with an ODS column, and the chemical structure was determined by NMR analysis. On the GC-MS analysis with a DB-23 column, the positional isomers were also eluted separately and characteristic mass spectra were proposed. By comparing the spectral data of the epoxy compounds with a different carbon chain, diagnostic fragment ions reflecting the chemical structure were determined as follows: m/z 79, 109, 113, and M-114 for the 6,7-epoxydienes; m/z 69, 97, 111, 139, and M-111 for the 9,10-epoxydienes; m/z 57, 79, 109, 136, M-151, and M-111 for the 11,12-epoxydienes; m/z 79, 91, 105, and 119 for the 3,4-epoxytrienes; m/z 79, 124, M-124, M-96, and M-69 for the 6,7-epoxytrienes; m/z 79, 95, 109, 137, and M-108 for the 9,10-epoxytrienes; and m/z 79, 134, M-149, M-109, and M-95 for the 11,12-epoxytrienes.

Sex pheromones of three citrus leafrollers, Archips atrolucens, Adoxophyes privatana, and Homona sp., inhabiting the Mekong Delta of Vietnam

Archips atrolucens, Adoxophyes privatana, and Homona sp. are serious defoliators of citrus trees in the Mekong Delta of Vietnam. In order to establish a sustainable pest-management program for the three species, their female-produced sex pheromones were investigated by GC-EAD and GC-MS analyses, and the following multi-component pheromones were identified: (Z)-11-tetradecenyl acetate (Z11-14:OAc), (E)-11-tetradecenyl acetate (E11-14:OAc), and tetradecyl acetate (14:OAc) in a ratio of 64:32:4 for A. atrolucens; Z11-14:OAc and (Z)-9-tetradecenyl acetate (Z9-14:OAc) in a ratio of 92:8 for A. privatana; and Z11-14:OAc and (Z)-9-dodecenyl acetate (Z9-12:OAc) in a ratio of 96:4 for Homona sp. Each lure baited with synthetic components as a mimic of the natural pheromone attracted males of the target species specifically, indicating that each monounsaturated minor component plays a significant role for mating communication and reproductive isolation of the three species inhabiting the same citrus orchards. In an extract of the pheromone glands of A. atrolucens females, the content of 14:OAc was very low, but a synergistic effect was observed clearly when the saturated compound was mixed at the same level as the E11-14:OAc. The synthetic lures will provide useful tools for monitoring flights of adults of the three species.

(E)-5-hexadecenyl acetate: a novel moth sex pheromone component from Stathmopoda auriferella

The sex pheromone of Stathmopoda auriferella (Walker), an important pest of kiwifruit in Korea, was studied. Two candidate pheromone components detected in the gland extracts of females were identified as (E)-5-hexadecenyl acetate (E5-16:OAc) and (E)-5-hexadecenol (E5-16:OH) in a ratio of 75:25 by mass spectral analysis of natural pheromone components and dimethyldisulfide adducts, and retention index comparisons with synthetic standards. In the kiwifruit orchards, E5-16:OAc alone was attractive to S. auriferella males and caught significantly more males than live virgin females. However, addition of E5-16:OH strongly inhibited attraction to E5-16:OAc. These results suggest that the major component of the female-produced sex pheromone of S. auriferella is E5-16:OAc. This hexadecenyl acetate is a novel moth sex pheromone component.

Identification of the sex pheromone secreted by a nettle moth, Monema flavescens, using gas chromatography/fourier transform infrared spectroscopy

The nettle moth Monema flavescens (Limacodidae) is a defoliator of fruit trees, such as Chinese plum and persimmon. The larvae of this species have spines containing a poison that causes serious irritation and inflammation in humans. Coupled gas chromatography-electroantennogram detection and gas chromatography/mass spectrometry analyses of a crude pheromone extract, combined with derivatization, indicated that female moths produced 8-decen-1-ol and 7,9-decadien-1-ol at a ratio of approximately 9:1. The E configuration of the double bonds was assigned for both components from infrared spectra, recorded on a gas chromatograph/Fourier transform-infrared spectrophotometer equipped with a zinc selenide disk cooled to -30 °C. The monoenyl and dienyl alcohols had absorptions characteristic of E geometry at 966 and 951 cm(-1), respectively. A band chromatogram at 951 cm(-1) was useful for distinguishing geometric isomers, because terminal conjugated diene are difficult to resolve, even on high polarity columns. Furthermore, we identified the Z configuration of the same 7,9-dienyl alcohol secreted by another nettle moth, Parasa lepida lepida, through the absence of this absorption. In field trials, lures baited with a 9:1 mixture of (E)-8-decen-1-ol and (E)-7,9-decadien-1-ol attracted M. flavescens males. Furthermore, the field trials indicated that contamination with the (Z)-diene reduced catches to the pheromone mixture more than did contamination with the (Z)-monoene.

Female sex pheromone secreted by Carmenta mimosa (Lepidoptera: Sesiidae), a biological control agent for an invasive weed in Vietnam

Larvae of the clearwing moth, Carmenta mimosa (Lepidoptera: Sesiidae), bore into the trunk of Mimosa pigra L., which is one of the most invasive weeds in Vietnam. GC-EAD and GC-MS analyses of a pheromone gland extract revealed that the female moths produced (3Z,13Z)-3,13-octadecadienyl acetate. A lure baited with the synthetic acetate alone successfully attracted C. mimosa males in a field test. While the addition of a small amount of the corresponding alcohol did not strongly diminish the number of captured males, a trace of the aldehyde derivative or the (3E,13Z)-isomer markedly inhibited the attractiveness of the acetate. The diurnal males were mainly attracted from 6:00 am to 12:00 am.