Sex Pheromone Compounds Research Articles

Disrupting the olfactory response in Monochamus saltuarius: Two potential target genes for controlling the vector insect of pine wilt disease.

Worldwide, pine forests have been threatened by a devastating pine wood disease caused by Bursaphelenchus xylophilus, with Monochamus saltuarius being a newly recorded vector of the disease in Northeast China. The olfactory system plays important roles in both feeding and oviposition during the adult stage of M.saltuarius, and olfactory gene function research is essential for gaining an understanding of the olfactory mechanisms of this pest. However, there is limited information available regarding olfactory gene functions in this pest. In the present study, we selected 7 olfactory genes, including 2 chemosensory proteins, 2 odorant-binding proteins, the odorant co-receptor and 2 odorant receptors, which were relatively highly expressed during the adult stage. We silenced these genes by RNA interference (RNAi), and real-time quantitative PCR was used to detect their expression levels after double-stranded RNA (dsRNA) injection. The results indicate that these genes were significantly downregulated at 2d post-dsRNA injection, and this was sustained until 5d post-injection. Electroantennography tests indicated that the knockdown of MsalOBP14 and MsalOrco impaired the olfactory response of M.saltuarius to 11 host volatiles and 1 sex pheromone compound. Y-tube experiments further confirmed that downregulated MsalOBP14 and MsalOrco expression led to olfactory dysfunction in M.saltuarius, which significantly lost selectivity. The results indicate that MsalOBP14 and MsalOrco play critical roles in sex communication and host volatile detection in M.saltuarius, and possibly represent 2 effective targets for controlling this forest pest through olfactory disruption.

Functional characterization of sex pheromone receptors PflaOR29 and PflaOR44 involved in the chemoreception of a diurnal moth, Phauda flammans (Walker) (Lepidoptera: Phaudidae)

Recognition of sex pheromones released by heterosexual moths via sex pheromone receptors is key for establishing mating connections in moths. The day-flying moth Phauda flammans is an oligophagous pest in southern cities of China and Southeast Asian countries. Our previous study reported that male P. flammans can be attracted to two sex pheromone compounds [Z-9-hexadecenal and (Z, Z, Z)-9,12,15-octadecadienal] released by females in the field; however, the mechanism of olfactory recognition is not clear. In this study, two sex pheromone receptor genes (PflaOR29 and PflaOR44) were cloned. Among the different tissues, both PflaOR29 and PflaOR44 were highly expressed in the antennae of mated male adults. At different developmental stages, the expression levels of PflaOR29 and PflaOR44 were significantly greater in mated male adults than other stages. The fluorescence signals of PflaOR29 and PflaOR44 were mostly distributed on the dorsal side of the antennae, with a large number of trichoid sensilla. The results of the gene function of PflaOR29 and PflaOR44 based on a Drosophila empty neuron heterologous expression system indicated that PflaOR29 strongly responded to (Z, Z, Z)-9,12,15-octadecadienal but not to Z-9-hexadecenal, whereas PflaOR44 did not respond to the two sex pheromones. Our findings clarify the sex pheromone receptor gene corresponding to (Z, Z, Z)-9,12,15-octadecatrienal. These results provide essential information for analyzing the mechanism of sexual communication in diurnal moths and for identifying target genes for the development of efficient attractants.

Region-Specific Variation in the Electrophysiological Responses of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Synthetic Sex Pheromone Compounds.

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a global pest that feeds on > 350 plant species and causes major yield loses. Variation in the responses of S. frugiperda males to female sex pheromone compounds affects the detection, monitoring and management of the pest. We determined geographic variation in the responses of S. frugiperda males to four different doses of synthetic sex pheromone compounds using a gas chromatography-electroantennogram detector (GC-EAD). Furthermore, we disentangled regional populations into C- and R- mitotypes via molecular analysis of the cytochrome oxidase I gene, and measured their responses to the compounds. When comparing responses of males from Florida, Benin, Nigeria and Kenya, we found some regional differences in the responses of S. frugiperda males to the major compound, Z9-14:OAc and minor component Z9-12:OAc. However, we found no differences in male responses between the different African countries. All males showed significantly higher antennal responses to Z7-12:OAc than to E7-12:OAc. When comparing the mitotypes, we found that Florida R-type males showed higher responses to Z9-14:OAc, Z7-12:OAc and Z9-12:OAc than Benin R-type males, while C-type males from both regions responded equally to Z7-12:OAc. In addition, Florida R-type males showed higher responses to E7-12:OAc than Florida C-type males. Our study thus shows some differential physiological responses of S. frugiperda males towards the known sex pheromone compounds, including E7-12:OAc, but mostly in the different mitotypes. How these differences translate to field trap catches remains to be determined.

Lipases and carboxylesterases affect moth sex pheromone compounds involved in interspecific mate recognition

Moth sex pheromones are a classical model for studying sexual selection. Females typically produce a species-specific pheromone blend that attracts males. Revealing the enzymes involved in the interspecific variation in blend composition is key for understanding the evolution of these sexual communication systems. The nature of the enzymes involved in the variation of acetate esters, which are prominent compounds in moth pheromone blends, remains unclear. We identify enzymes involved in acetate degradation using two closely related moth species: Heliothis (Chloridea) subflexa and H. (C.) virescens, which have different quantities of acetate esters in their sex pheromone. Through comparative transcriptomic analyses and CRISPR/Cas9 knockouts, we show that two lipases and two esterases from H. virescens reduce the levels of pheromone acetate esters when expressed in H. subflexa females. Together, our results show that lipases and carboxylesterases are involved in tuning Lepidoptera pheromones composition.

Diet-derived male sex pheromone compounds affect female choice in a noctuid moth.

Sexual signals often function in species recognition and may also guide mate choice within a species. In noctuid moths, both males and females may exercise mate choice. Females of the tobacco budworm Chloridea virescens prefer to mate with larger males, but the signal(s) underlying female choice remain unknown. Male hairpencil volatiles are emitted during close range courtship displays. However, previously identified male hairpencil volatiles, namely acetate esters, aldehydes, alcohols, and fatty acids, are not associated with female choice. Recently, two new hairpencil compounds were identified that elicit strong electrophysiological responses in female antennae: methyl salicylate (MeSA) and δ-decalactone. In this study, we investigated the effect of larval diet and adult feeding on MeSA and δ-decalactone content in hairpencils and determined whether these compounds are involved in female choice. We found that larval diet affected MeSA content in hairpencils, but not δ-decalactone. Conversely, adult feeding affected the level of δ-decalactone, but not MeSA: sugar-water feeding increased δ-decalactone content compared to plain water. In two-choice assays, females mated more with males that had higher amounts of δ-decalactone, and less with males with higher amounts of MeSA.

Stored product pest Nemapogon variatella (Clemens): Identification of sex pheromone, putative antagonist and mitotype characterization

AbstractNemapogon variatella (Clemens) (Lepidoptera: Tineidae) is a worldwide widespread stored product pest that damages grain, dried fruits and mushrooms. The most powerful and environmentally friendly tool for insect pest monitoring and control is pheromone application. In our study, we revealed for the first time that the females of N. variatella release (3Z,13Z)‐octadecadien‐1‐ol – a single compound that activates olfactory receptors in the antenna of conspecific males. These data allow to assign this compound, which has been known as an attractant for males only, to the category of sex pheromones of N. variatella moths. Males' olfactory system is sensitive not only to the sex pheromone compound but also to (3E,13Z)‐octadecadien‐1‐ol as well. (3E,13Z)‐octadecadien‐1‐ol is attributed to putative pheromone antagonists. During the analysis of genetic diversity, six mitotypes of N. variatella CO1‐5′ were detected and preliminary named Mit1–Mit6. The obtained high haplotype diversity (Hd = 0.796) and low nucleotide diversity (Pi = 0.007) suggest that this species may have undergone a recent population expansion.

Identification of an odorant receptor responding to sex pheromones in Spodoptera frugiperda extends the novel type-I PR lineage in moths.

In moths, pheromone receptors (PRs) are crucial for intraspecific sexual communication between males and females. Moth PRs are considered as an ideal model for studying the evolution of insect PRs, and a large number of PRs have been identified and functionally characterized in different moth species. Moth PRs were initially thought to fall into a single monophyletic clade in the odorant receptor (OR) family, but recent studies have shown that ORs in another lineage also bind type-I sex pheromones, which indicates that type-I PRs have multiple independent origins in the Lepidoptera. In this study, we investigated whether ORs of the pest moth Spodoptera frugiperda belonging to clades closely related to this novel PR lineage may also have the capacity to bind type-I pheromones and serve as male PRs. Among the 7 ORs tested, only 1 (SfruOR23) exhibited a male-biased expression pattern. Importantly, invitro functional characterization showed that SfruOR23 could bind several type-I sex pheromone compounds with Z-9-tetradecenal (Z9-14:Ald), a minor component found in female sex pheromone glands, as the optimal ligand. In addition, SfruOR23 also showed weak responses to plant volatile organic compounds. Altogether, we characterized an S.frugiperda PR positioned in a lineage closely related to the novel PR clade, indicating that the type-I PR lineage can be extended in moths.

Functional Characterization of Pheromone Receptors in the Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae).

Lepidopteran insects mainly rely on sex pheromones to complete sexual communications. Pheromone receptors (PRs) are expressed on the olfactory receptor neurons (ORNs) of the sensilla trichodea and play an essential role in sexual communication. Despite extensive investigations into the mechanisms of peripheral recognition of sex pheromones in Lepidoptera, knowledge about these mechanisms in L. sticticalis remains limited. In this study, five candidate LstiPRs were analyzed in a phylogenetic tree with those of other Lepidopteran insects. Electroantennography (EAG) assays showed that the major sex pheromone component E11-14:OAc elicited a stronger antennal response than other compounds in male moths. Moreover, two types of neurons in sensilla trichodea were classified by single sensillum recordings, of which the "a" neuron specifically responded to E11-14:OAc. Five candidate PRs were functionally assayed by the heterologous expression system of Xenopus oocytes, and LstiPR2 responded to the major sex pheromone E11-14:OAc. Our findings suggest that LstiPR2 is a PR sensitive to L. sticticalis's major sex pheromone compound, E11-14:OAc. Furthermore, this study offers valuable insights into the sexual communication behavior of L. sticticalis, forming a foundation for further analysis of the species' central nervous system.

More to legs than meets the eye: Presence and function of pheromone compounds on heliothine moth legs.

Chemical communication is ubiquitous in nature and chemical signals convey species-specific messages. Despite their specificity, chemical signals may not be limited to only one function. Identifying alternative functions of chemical signals is key to understanding how chemical communication systems evolve. Here, we explored alternative functions of moth sex pheromone compounds. These chemicals are generally produced in, and emitted from, dedicated sex pheromone glands, but some have recently also been found on the insects' legs. We identified and quantified the chemicals in leg extracts of the three heliothine moth species Chloridea (Heliothis) virescens, Chloridea (Heliothis) subflexa and Helicoverpa armigera, compared their chemical profiles and explored the biological function of pheromone compounds on moth legs. Identical pheromone compounds were present on the legs in both sexes of all three species, with no striking interspecies or intersex differences. Surprisingly, we also found pheromone-related acetate esters in leg extracts of species that lack acetate esters in their female sex pheromone. When we assessed gene expression levels in the leg tissue, we found known and putative pheromone-biosynthesis genes expressed, which suggests that moth legs may be additional sites of pheromone production. To determine possible additional roles of the pheromone compounds on legs, we explored whether these may act as oviposition-deterring signals, which does not seem to be the case. However, when we tested whether these chemicals have antimicrobial properties, we found that two pheromone compounds (16:Ald and 16:OH) reduce bacterial growth. Such an additional function of previously identified pheromone compounds likely coincides with additional selection pressures and, thus, should be considered in scenarios on the evolution of these signals.

Sex Pheromone Receptor-Derived Peptide Biosensor for Efficient Monitoring of the Cotton Bollworm Helicoverpa armigera.

The cotton bollworm, Helicoverpa armigera (H. armigera), causes damage to a wide range of cultivated crops and is one of the pests with the greatest economic importance for global agriculture. Currently, the detection of H. armigera is based on manual sampling. A low limit of detection (LOD), convenient, and real-time monitoring method is urgently needed for its early warning and efficient management. Here, we characterized the amino acid sequence in the sex pheromone receptors (SPRs) recognizing the pheromone components of H. armigera by three-dimensional (3D) modeling and molecular docking. Next, sex pheromone receptor-derived peptides (SPRPs) were synthesized and conjugated to nanotubes by chemical connection. The modified nanotubes were used to fabricate a sensor capable of real-time monitoring of gaseous sex pheromone compounds with a low LOD (∼10 ppb for Z11-16:Ald) and selectivity, and the sensor was able to detect a single live H. armigera. Furthermore, the developed biosensor allowed direct monitoring of the pheromone release dynamics by female H. armigera and showed that the release was instantly reduced in response to light. Here, we report the first demonstration of a biosensing method for detecting gaseous sex pheromones and live H. armigera. The findings show the great potential of the SPRP sensor for broad applications in insect biology study and infestation monitoring.

Characterization of Two Aldehyde Oxidases from the Greater Wax Moth, Galleria mellonella Linnaeus. (Lepidoptera: Pyralidae) with Potential Role as Odorant-Degrading Enzymes.

Odorant-degrading enzymes (ODEs) are proposed to degrade/inactivate volatile organic compounds (VOCs) on a millisecond timescale. Thus, ODEs play an important role in the insect olfactory system as a reset mechanism. The inhibition of these enzymes could incapacitate the olfactory system and, consequently, disrupt chemical communication, promoting and complementing the integrated pest management strategies. Here, we report two novel aldehyde oxidases, AOX-encoding genes GmelAOX2 and GmelAOX3, though transcriptomic analysis in the greater wax moth, Galleria mellonella. GmelAOX2 was clustered in a clade with ODE function, according to phylogenetic analysis. Likewise, to unravel the profile of volatiles that G. mellonella might face besides the sex pheromone blend, VOCs were trapped from honeycombs and the identification was made by gas chromatography-mass spectrometry. Semi-quantitative RT-PCR showed that GmelAXO2 has a sex-biased expression, and qRT-PCR indicated that both GmelAOX2 and GmelAOX3 have a higher relative expression in male antennae rather than female antennae. A functional assay revealed that antennal extracts had the strongest enzymatic activity against undecanal (4-fold) compared to benzaldehyde (control). Our data suggest that these enzymes have a crucial role in metabolizing sex pheromone compounds as well as plant-derived aldehydes, which are related to honeycombs and the life cycle of G. mellonella.

Functional disparity of four pheromone-binding proteins from the plum fruit moth Grapholita funebrana Treitscheke in detection of sex pheromone components

Grapholita funebrana, also known as the plum fruit moth, is an oligophagous pest species that causes enormous economic losses of the fruits of Rosaceae. An eco-friendly method for the control of G. funebrana besides chemical control has not yet been developed. The sex pheromone communication system plays an important role in moth courtship and mating, in which pheromone-binding proteins (PBPs) are critical. In this research, we identified four PBPs, namely, GfunPBP1.1, GfunPBP1.2, GfunPBP2, and GfunPBP3, from the antennae of G. funebrana. The results of real-time quantitative PCR (RT-qPCR) showed that all four GfunPBPs were overwhelmingly expressed in the antennae and that GfunPBP1.2 and GfunPBP2 showed male-biased expression patterns, whereas GfunPBP1.1 and GfunPBP3 were equally expressed between sexes. The results of ligand-binding assays illustrated that although all four recombinant GfunPBPs (rGfunPBPs) had binding activity with the tested sex pheromone compounds, their preferred ligands were significantly different. rGfunPBP2 had the strongest binding affinity to Z8–12:Ac and Z8–12:OH; rGfunPBP1.1 preferred to bind Z8–14:Ac, Z10–14:Ac, and 12:OH more than to the other three GfunPBPs; and rGfunPBP1.2 exhibited stronger binding affinity to E8–12:Ac than to the other rGfunPBPs. Molecular docking results demonstrated that hydrophobic forces, especially van der Waals forces and hydrogen bonds, were the most important forces that maintained GfunPBP–pheromone ligand complexes. This study will improve our understanding of the sex pheromone recognition mechanisms of G. funebrana and promote the development of novel strategies for controlling G. funebrana.

Transcriptional deregulation of stress-growth balance in Nicotiana benthamiana biofactories producing insect sex pheromones.

Plant biofactories are a promising platform for sustainable production of high-value compounds, among which are insect sex pheromones, a green alternative to conventional insecticides in agriculture. Recently, we have constructed transgenic Nicotiana benthamiana plants ("Sexy Plants", SxP) that successfully produce a blend of moth (Lepidoptera) sex pheromone compounds (Z)-11-hexadecen-1-ol and (Z)-11-hexadecenyl acetate. However, efficient biosynthesis of sex pheromones resulted in growth and developmental penalty, diminishing the potential for commercial use of SxP in biomanufacturing. To gain insight into the underlying molecular responses, we analysed the whole-genome transcriptome and evaluated it in relation to growth and pheromone production in low- and high-producing transgenic plants of v1.0 and v1.2 SxP lines. In our study, high-producing SxPv1.2 plants accumulated the highest amounts of pheromones but still maintained better growth compared to v1.0 high producers. For an in-depth biological interpretation of the transcriptomic data, we have prepared a comprehensive functional N. benthamiana genome annotation as well as gene translations to Arabidopsis thaliana, enabling functional information transfer by using Arabidopsis knowledge networks. Differential gene expression analysis, contrasting pheromone producers to wild-type plants, revealed that while only a few genes were differentially regulated in low-producing plants, high-producing plants exhibited vast transcriptional reprogramming. They showed signs of stress-like response, manifested as downregulation of photosynthesis-related genes and significant differences in expression of hormonal signalling and secondary metabolism-related genes, the latter presumably leading to previously reported volatilome changes. Further network analyses confirmed stress-like response with activation of jasmonic acid and downregulation of gibberellic acid signalling, illuminating the possibility that the observed growth penalty was not solely a consequence of a higher metabolic burden imposed upon constitutive expression of a heterologous biosynthetic pathway, but rather the result of signalling pathway perturbation. Our work presents an example of comprehensive transcriptomic analyses of disadvantageous stress signalling in N. benthamiana biofactory that could be applied to other bioproduction systems.

Moth sex pheromones affect interspecific competition among sympatric species and possibly population distribution by modulating pre-mating behavior.

Premating behaviors mediated by pheromones play pivotal roles in animal mating choices. In natural populations of the striped stem borer Chilo suppressalis and the rice leaf roller Cnaphalocrocis medinalis in the rice field habitat, we discovered that Z11-16:Ald, a major component of the C. suppressalis pheromone, modulated the premating behavior of C. medinalis. Z11-16:Ald evoked a strong olfactory response in male antennae and strongly inhibited the sex pheromone trapping of male C. medinalis in the field. The functions of three C. medinalis sex pheromone receptor genes (CmedPR1-3) were verified through heterologous expression in Xenopus oocytes. CmedPR1 responded to Z11-18:OH and Z11-18:Ald, as well as the interspecific pheromone compound Z11-16:Ac of sympatric species; CmedPR2 responded to Z13-18:OH and Z13-18:Ald, as well as the sex pheromone compounds Z11-16:Ald and Z9-16:Ald of sympatric species; and CmedPR3 responded to Z11-18:OH and Z13-18:OH, as well as the interspecific pheromones Z11-16:OH, Z9-16:Ald, Z11-16:Ac, and Z11-16:Ald of sympatric species. Thus, CmedPR2 and CmedPR3 share the ligand Z11-16:Ald, which is not a component of the C. medinalis sex pheromone. Therefore, the sex pheromones of interspecific species affected the input of neural signals by stimulating the sex pheromone receptors on the antennae of male C. medinalis moths, thereby inhibiting the olfactory responses of the male moths to the sex pheromones. Our results demonstrate chemical communication among sympatric species in the rice field habitat, the recognition of intra- and interspecific sex pheromones by olfactory receptors, and how insect premating behaviors are modulated to possibly affect resource partitioning.

An overview of studies on sex pheromones of insect vectors of pathogenic trypanosomatids of medical and veterinary importance

Insect vectors of Leishmaniases, Chagas disease and African trypanosomiasis remain human health, veterinary and economic problems worldwide. Several sex pheromones molecules that contribute to mating behavior have been identified in these vectors. These chemical signals are potential alternatives to traditional chemical insecticides. This review discusses the diversity of sex pheromone molecules and their role in the mating behavior of insect vectors of Leishmaniases, Chagas disease and African trypanosomiasis. The selection of studies was made based on research and review articles that presented sex pheromone aspects regarding insect vectors. In some species, these molecules have a dual function as serving as sex and aggregation pheromone. We also highlight the current knowledge of these substances as potential vector control tools. The studies revealed that sex pheromones applicability is largely experimental and restricted to some vectors. Based on these limitations, we included updated tables with the chemical identity of several sex pheromone compounds and other relevant information concerning the target species, which can contribute to future studies of control methodologies.

Analysis of sex pheromone production and field trapping of the Asian corn borer (Ostrinia furnacalis Guenée) in Xinjiang, China

Identifying the sex pheromone systems of local pest populations facilitates their management, especially for moth species that show significant geographic variation in sex pheromone communication. We investigated the pheromone production and behavioral responses of the Asian corn borer (Ostrinia furnacalis Guenée; ACB) in Xinjiang, China. The ACB produces three compounds: (Z)-12-tetradecenyl acetate (Z12-14:Ac) and (E)-12-tetradecenyl acetate (E12-14:Ac) which are two sex pheromone compounds, and n-tetradecyl acetate (14:Ac) which has variable roles in mediating behavioral responses. The ratios of these three compounds produced in female gland are geographically distinct among different populations. Quantitative analysis of pheromone production showed that the proportions of Z12-14:Ac in the E/Z isomers (i.e., Z and E12-14:Ac) and the proportions of 14:Ac in the ternary blend respectively averaged 60.46% (SD=5.26) and 25.00% (SD=7.37), with their probabilities normally or near-normally distributed. Trapping experiments in a cornfield indicated that deploying the E/Z isomers and the three compounds in rubber septa close to their gland ratios yielded the most captured males, while other ratios that deviated from the gland ratios showed reduced field captures. The ternary blend was significantly more attractive to males than the E/Z isomers in the field, indicating a functional role of 14:Ac as the third pheromone component used by the local population. Additionally, the dose-response test demonstrated that the application of the three compounds at dosages between 200 and 350 μg attracted significantly more males compared to other dosages. Therefore, the characterization of this local ACB pheromone system provides additional information about its geographic variation and serves as a basis for optimizing the pheromone-mediated control of this pest in Xinjiang.

Identification of Chemosensory Genes, Including Candidate Pheromone Receptors, in Phauda flammans (Walker) (Lepidoptera: Phaudidae) Through Transcriptomic Analyses.

Olfactory and gustatory systems play an irreplaceable role in all cycles of growth of insects, such as host location, mating, and oviposition. Many chemosensory genes in many nocturnal moths have been identified via omics technology, but knowledge of these genes in diurnal moths is lacking. In our recent studies, we reported two sex pheromone compounds and three host plant volatiles that play a vital role in attracting the diurnal moth, Phauda flammans. The antennal full-length transcriptome sequence of P. flammans was obtained using the Pacbio sequencing to further explore the process of sex pheromone and host plant volatile recognition in P. flammans. Transcriptome analysis identified 166 candidate olfactory and gustatory genes, including 58 odorant-binding proteins (OBPs), 19 chemosensory proteins (CSPs), 59 olfactory receptors (ORs), 16 ionotropic receptors (IRs), 14 gustatory receptors (GRs), and 2 sensory neuron membrane proteins (SNMPs). Subsequently, a phylogenetic tree was established using P. flammans and other lepidopteran species to investigate orthologs. Among the 17 candidate pheromone receptor (PR) genes, the expression levels of PflaOR21, PflaOR25, PflaOR35, PflaOR40, PflaOR41, PflaOR42, PflaOR44, PflaOR49, PflaOR51, PflaOR61, and PflaOR63 in the antennae were significantly higher than those in other non-antennae tissues. Among these PR genes, PflaOR21, PflaOR27, PflaOR29, PflaOR35, PflaOR37, PflaOR40, PflaOR42, PflaOR44, PflaOR60, and PflaOR62 showed male-biased expression, whereas PflaOR49, PflaOR61, and PflaOR63 revealed female-biased expression. The functions of related OR genes were also discussed. This research filled the gap of the chemosensory genes of P. flammans and provided basic data for future functional molecular mechanisms studies on P. flammans olfaction.

Enhancement of attraction to sex pheromone of Grapholita molesta (Busck) (Lepidoptera: Tortricidae) by structurally unrelated sex pheromone compounds of Conogethes punctiferalis (Guenée) (Lepidoptera: Crambidae)

• OFM and C. punctiferalis are sympatric moth species in orchards. • The two moths belong to different families and use completely different pheromone compounds. • Pheromone compounds of C. punctiferalis elicited antennal responses in OFM males. • The interspecific pheromone compounds also enhanced pheromone attraction of OFM. • Field responses suggested additional semiochemicals for pheromone-based control for OFM. Grapholita molesta (Busck) (the oriental fruit moth; OFM) and Conogethes punctiferalis (Guenée) are both fruit and stem borers with overlapping habitats, occurrences, and outbreak cycles. These two species are in different families and they have completely different sex pheromone components. Here, the effects of the sex pheromone components of C. punctiferalis , ( E )-10-hexadecenal ( E 10-16:Ald) and ( Z )-10-hexadecenal ( Z 10-16:Ald) and their mixture, were evaluated on the sexual communication of OFM by examining electrophysiological (EAG) and behavioral responses. We found that a considerably large amount of E 10-16:Ald or Z 10-16:Ald and a tiny amount of OFM pheromone elicited comparable EAG responses in OFM males, indicating the low antennal olfactory sensitivity of OFM males to the heterospecific pheromone compounds. In two different peach orchard parcels, captures of OFM by their pheromone lures baited in delta traps were increased by at least 1.5 times when OFM pheromone lures were combined with lures that contained 1000 μg of either E 10-16:Ald, Z 10-16:Ald or their mixture. In two other pear orchard parcels, both E 10-16:Ald and Z 10-16:Ald increased captures of OFM in Unitraps in a dose-dependent manner with more than a four-fold increase. Therefore, the enhanced attractiveness of OFM lures by the two interspecific pheromones suggests their potential application to improve mass trapping, population monitoring and mating disruption of OFM.

Cumulative effects of sex pheromone components in mate recognition of Muscidifurax raptorellus

AbstractIn insects, chemical information is often crucial for mate recognition. The chemical signal may be perceived already from a distance or only at close range, depending on the volatility of the sex pheromone compounds. In many species, close‐range mate recognition is mediated by compounds of low volatility that originate from the insects’ cuticular lipid layer. The most prominent constituents are usually non‐polar hydrocarbons, but other, more polar compounds can be present as well. Upon detection, these lipids can elicit courtship behaviour. We studied mate recognition in the parasitoid wasp Muscidifurax raptorellus Kogan & Legner (Hymenoptera: Pteromalidae). In this species, courtship behaviour starts with bouts of wing fanning (high frequency wing beats while standing or walking). Once the male has mounted the female, he shows stereotypical antennal movements (antennal courtship) that lead to female receptivity signalling and copulation. We investigated the role of chemical compounds for mate recognition by evaluating the reaction of male M. raptorellus towards live conspecifics and dummies treated with whole‐body extracts or with extract fractions (non‐polar, intermediately polar, and polar compounds) in bioassays. Our results indicate that despite the sex specificity of cuticular hydrocarbon profiles, these compounds alone are not sufficient for mate recognition. Rather, we found that cuticular lipids of all three fractions seem to constitute the mate recognition signal, with a ternary mixture eliciting wing fanning significantly more often than single fractions. Overall, our results suggest that the three lipid fractions contribute cumulatively to the mate recognition signal.

Sex pheromone receptors of the light brown apple moth, Epiphyas postvittana, support a second major pheromone receptor clade within the Lepidoptera

Sex pheromones facilitate species-specific sex communication within the Lepidoptera. They are detected by specialised pheromone receptors (PRs), most of which to date fall into a single monophyletic receptor lineage (frequently referred to as “the PR clade”) within the odorant receptor (OR) family. Here we investigated PRs of the invasive horticultural pest, Epiphyas postvittana, commonly known as the light brown apple moth. Ten candidate PRs were selected, based on their male-biased expression in antennae or their relationship to the PR clade, for functional assessment in both HEK293 cells and Xenopus oocytes. Of these, six ORs responded to compounds that include components of the E. postvittana (‘Epos’) sex pheromone blend or compounds that antagonise sex pheromone attraction. In phylogenies, four of the characterised receptors (EposOR1, 6, 7 and 45) fall within the PR clade and two other male-biased receptors (EposOR30 and 34) group together well outside the PR clade. This new clade of pheromone receptors includes the receptor for (E)-11-tetradecenyl acetate (EposOR30), which is the main component of the sex pheromone blend for this species. Interestingly, receptors of the two clades do not segregate by preference for compounds associated with behavioural response (agonist or antagonist), isomer type (E or Z) or functional group (alcohol or acetate), with examples of each scattered across both clades. Phylogenetic comparison with PRs from other species supports the existence of a second major clade of lepidopteran ORs including, EposOR30 and 34, that has been co-opted into sex pheromone detection in the Lepidoptera. This second clade of sex pheromone receptors has an origin that likely predates the split between the major lepidopteran families.