Molecular basis of (E)-β-farnesene-mediated aphid location in the predator Eupeodes corollae

Structural Basis and Recognition Mechanism of Host-Derived Volatiles by Olfactory Proteins in the Agricultural Pest Bactrocera correcta (Diptera: Tephritidae)

Host-derived volatiles play a critical role in mediating plant-insect interactions. Bactrocera correcta is a destructive pest of fruit crops. In this study, we investigated the recognition mechanisms of three key volatiles─β-caryophyllene, ethyl decanoate, and hexyl hexanoate─derived from the host fruits of B. correcta. Using transcriptomic analysis, fluorescence binding assays, molecular docking, and molecular dynamics simulations, we identified BcorOBP19d-2 as a key odorant-binding protein that binds multiple volatiles and facilitates their stabilization and transport. Odorant receptors (BcorOR7a-13, BcorOR74a-3, and BcorOR7a-3) selectively recognize these volatiles, with hydrophobic interactions as the primary driving force for binding. β-Caryophyllene exhibited the highest binding specificity with BcorOR7a-13, ethyl decanoate demonstrated the strongest binding affinity with BcorOR74a-3, and hexyl hexanoate showed moderate stability with BcorOR7a-3. These findings provide structural insights into volatile recognition in polyphagous insects and offer a basis for developing attractants or repellents for pest management.

Genomics of insect natural enemies in agroecosystems

Currently, a wealth of genomic data are now accessible for numerous insect natural enemies, serving as valuable resources that deepen our understanding of the genetic basis of biocontrol traits in these organisms. We summarize the current state of genome sequencing and highlight candidate genes related to biocontrol traits that hold promise for genetic improvement. We also review the recent population genomic studies in biological control and the discovery of potential insecticidal genes in parasitoid wasps. Collectively, current genomic works have shown the powerful ability to identify candidate genes responsible for desirable traits or promising effectors. However, further functional study is necessary to gain a mechanistic understanding of these genes, and future efforts are also needed to develop suitable approaches to translate genomic insights into field applications.

Bacterial volatiles from aphid honeydew mediate ladybird beetles oviposition site choice

BACKGROUND

The cotton-melon aphid Aphis gossypii Glover is a destructive pest worldwide that causes substantial damage to diverse crops. The ladybird beetle Propylea japonica Thunberg is the dominant predatory natural enemy of A. gossypii. To date, the chemical cues of P. japonica associated with the selection of oviposition sites remain unclear.

RESULTS

Our results revealed that crude honeydew, but not sterilized honeydew, was strongly attractive to mated P. japonica. A total of eight bacterial strains were isolated from crude honeydew, with two (Acinetobacter sp. and Pseudomonas sp.) showing significant attractiveness. Volatiles from these bacteria were identified, and three compounds-DL-lactic acid, 4, 6-dimethyl-2-heptanone, and didodecyl phthalate-were found to significantly attract mated P. japonica in olfactometer assays. Further cage experiments confirmed that P. japonica preferred oviposition sites near these volatile substances.

CONCLUSION

The oviposition site selection by the ladybird beetle P. japonica was found to be influenced by volatiles produced by bacteria associated with cotton-melon aphid honeydew. These findings contribute to biologically based, environmentally friendly pest management strategies in agriculture. © 2025 Society of Chemical Industry.

Diversity and role of volatile terpene and terpenoid pheromones in insects

Insect pheromones are critical chemical signals that regulate intraspecific behavior and play a key role in the dynamic monitoring and control of pest populations. Historically, research on insect pheromones has primarily focused on lipid-based compounds. However, terpenes and terpenoids, which are widely occurring classes of bioactive compounds, also play significant roles in insect pheromone blends. Over 50 terpene and terpenoid-based pheromones have been identified in over 52 insect species, spanning various orders such as Coleoptera, Hymenoptera, Blattodea, Hemiptera, Diptera, and Lepidoptera. These compounds are associated with several types of pheromones, including female or male sex pheromones, aggregation pheromones, alarm pheromones, and aphrodisiac pheromones. Terpenes and terpenoids may act as either primary or secondary components of pheromone blends and influence a wide range of critical insect behaviors. They play essential roles in the physiological and ecological adaptation of insects to their environment. This review provides a comprehensive overview of current research on terpene and terpenoid-based pheromones in insects, examining their structures, types, and physiological and ecological functions. Additionally, we propose future research directions to guide the application of these pheromones in insect behavioral regulation and pest management, while advocating for their broader use in insect pest monitoring and control.

Yeast-derived volatiles orchestrate an insect-yeast mutualism with oriental armyworm moths

Interactions among insects, plants, and microorganisms are fundamental to ecosystem dynamics, with floral nectar and pollen serving as key resources for various organisms. Yeasts, such as Metschnikowia reukaufii, commonly found in nectar, influence nectarial attraction through volatile compounds (VOCs), yet the underlying biological mechanisms remain elusive. Here, we show that isoamyl alcohol, a prominent yeast VOC, attracts oriental armyworm moths (Mythimna separata) to pollen-rich, yeast-fermented nectar. In a series of electrophysiological and behavioral assays, we show that isoamyl alcohol activates a single class of highly specific olfactory sensory neurons expressing the olfactory receptor MsepOR8. In the moth antennal lobe, these neurons target the AM2 glomerulus, which responds to isoamyl alcohol. Genetic disruption of MsepOR8 leads to complete abolition of both physiological and behavioral responses to isoamyl alcohol, resulting in an impaired ability to locate nectar sources. Moreover, we show that isoamyl alcohol-induced foraging behavior fosters a mutualistic relationship between yeast and moths to some extent, enhancing yeast dispersal and increasing moth reproductive success. Our results unveil a highly specific mechanism by which a yeast-derived VOC facilitates insect-yeast mutualism, providing insights into insect-microbe interactions within pollination ecosystems.

The Hoverfly Attracting Property of a Methyl Salicylate-Containing (E)-β-Farnesene Analog (3e) and Potential Mechanism by Mediating the EcorOBP15 and EcorOR3

Using natural enemies provides a sustainable method to control major agricultural pests. Hoverflies are significant natural enemies of aphids and efficient pollinators. Herbivore-induced plant volatiles (HIPVs), including (E)-β-farnesene (EBF) and methyl salicylate (MeSA), are key olfactory cues mediating hoverflies behavior. Our previous work identified compound 3e, an EBF analog containing a MeSA moiety, exhibited aphid-repelling and ladybug-attracting activities. However, whether 3e can attract hoverflies remains unknown. Therefore, this study explored the attractant property and potential mechanism of 3e toward hoverflies. Laboratory bioassays and field trials indicated 3e has an obvious hoverfly attracting property. The attraction mechanism studies demonstrate that, similar to EBF, 3e can interact with EcorOBP15 and EcorOR3, with its greater chemical softness, larger hydrophobic and charge regions enhancing these interactions. Furthermore, 3e exhibited low toxicity to honeybees (Apis mellifera) and hoverflies (Eupeodes corollae). Consequently, 3e could be a promising eco-friendly behavioral regulator for integrated aphid management in sustainable agriculture.

Characterization of the ligand-binding properties of odorant-binding protein 38 from Riptortus pedestris when interacting with soybean volatiles

Background

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) is a major soybean pest throughout East Asia that relies on its advanced olfactory system for the perception of plant-derived volatile compounds and aggregation pheromones for conspecific and host plant localization. Odorant binding proteins (OBPs) facilitate the transport of odorant compounds across the sensillum lymph within the insect olfactory system, enabling their interaction with odorant receptors (ORs).

Methods

Real-time quantitative PCR (qRT-PCR) analyses, fluorescence-based competitive binding assays, and molecular docking analyses were applied to assess the expression and ligand-binding properties of OBP38 from R. peddestris.

Results

The qRT-PCR analyses revealed high levels of RpedOBP38 expression in the antennae without any apparent sex bias, and it was also highly expressed in the adult stage. Recombinant RpedOBP38 was prepared by expressing it in E. coli BL21 (DE3) followed by its purification with a Ni-chelating affinity column. RpedOBP38 was found to bind most strongly to trans-2-decenal (Ki = 7.440) and trans-2-nonenal (Ki = 10.973), followed by β-pinene, (+) -4-terpineol, carvacrol, methyl salicylate, and (-)-carvone. The 3D structure of RpedOBP38 contains six α-helices and three interlocked disulfide bridges comprising a stable hydrophobic binding pocket. In a final series of molecular docking analyses, several polar (e.g., His 94, Glu97) and nonpolar (e.g., Leu29, Ile59) residues were found to be involved in RpedOBP38-ligand binding.

Conclusion

These data support a role for RpedOBP38 in the perception of volatiles derived from host plants, providing important insight into the mechanisms that govern olfactory recognition in R. pedestris, thereby informing the development of ecologically friendly approaches to managing R. pedestris infestations.

The Role of (E)-β-Farnesene in Tritrophic Interactions: Biosynthesis, Chemoreception, and Evolution

(E)-β-farnesene (EBF) stands out as a crucial volatile organic compound, exerting significant influence on the complex interactions between plants, aphids, and predator insects. Serving as an alarm signal within aphids, EBF is also emitted by plants as a defense mechanism to attract aphid predators. This review delves into EBF sources, functions, biosynthesis, detection mechanisms, and its coevolutionary impacts on aphids and insect predators. The exploration underscores the need to comprehend the biophysical and structural foundations of EBF receptors in aphids, emphasizing their role in unraveling the intricate patterns and mechanisms of interaction between EBF and target receptors. Furthermore, we advocate for adopting structure-based or machine-learning methodologies to anticipate receptor-ligand interactions. On the basis of this knowledge, we propose future research directions aiming at designing, optimizing, and screening more stable and efficient active odorants. A pivotal outcome of this comprehensive investigation aims to contribute to the development of more effective aphid-targeted control strategies.

Behavioral responses of Araecerus fasciculatus (Coleoptera: Anthribidae) to volatiles of selected stored Chinese medicinal plant products

The olfactory responses of Araecerus fasciculatus Degeer to the volatiles of 5 traditional Chinese medicine plant products (CMPPs; i.e., Codonopsis pilosula Franch., Ophiopogon japonicus Linn. f., Astragalus membranaceus Fisch., Dendrobium nobile Lindl., and Angelica dahurica Fisch.) were studied using Y-tube, 4-arm, and 6-arm olfactometers. The volatile components of these CMPPs were analyzed using gas chromatography-mass spectrometry (GC-MS). A. fasciculatus significantly preferred the CMPPs volatiles in the order of O. japonicus > C. pilosula > A. membranaceus ≥ D. nobile = A. dahurica. In the volatile profiles of O. japonicus, C. pilosula, A. membranaceus, D. nobile, and A. dahurica, GC-MS identified 27, 61, 63, 52, and 71 components, respectively, and β-elemene (30.58%), hexanal (12.69%), selina-3,7(11)-diene (12.31%), d-limonene (18.59%), and α-curcumene (8.88%) were the most abundant volatile components. A. fasciculatus were attracted to β-elemene, α-selinene, and β-selinene (main components of the volatile profiles of the most preferred CMPPs of O. japonicus) at different concentrations, with 1, 50, and 25 µg/µl being the most attractive, respectively. The olfactory preferences of A. fasciculatus were β-elemene > α-selinene = β-selinene based on the 4-arm olfactometer bioassays for comparisons at their most attractive concentrations. Therefore, differences in the volatile profiles among CMPPs significantly influenced the olfactory responses of A. fasciculatus, offering insight into the mechanisms of host preferences in stored-product pests based on chemical ecology. β-elemene showed the greatest potential to be developed as an attractant for the monitoring and control of this pest.

Identification of miRNAs Involved in Olfactory Regulation in Antennae of Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

The beet webworm, Loxostege sticticalis, is a typical migratory pest. Although miRNAs participate in many physiological functions, little is known about the functions of miRNAs in olfactory regulation. In this study, 1120 (869 known and 251 novel) miRNAs were identified in the antennae of L. sticticalis by using high-throughput sequencing technology. Among the known miRNAs, 189 from 49 families were insect-specific, indicating that these miRNAs might play unique roles in insects. Furthermore, based on the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, we found that 3647 and 1393 miRNAs were associated with localization and the regulation of localization, respectively, and 80 miRNAs were enriched in the neuroactive ligand-receptor interaction pathway. These miRNAs might be involved in the olfactory system of L. sticticalis. Notably, qRT-PCR showed that most of the tested miRNAs presented similar expression patterns compared with the RNA-seq data and that miR-87-3, novel-miR-78, and novel-miR-142 were significantly differentially expressed in the antennae of males and females. In addition, 21 miRNAs were predicted to target 23 olfactory genes, including 10 odorant-binding proteins (OBPs), 3 chemosensory proteins (CSPs), 4 odorant receptors (ORs), 1 ionotropic receptor (IR), and 5 gustatory receptors (GRs). The olfactory-related miRNAs exhibited low-abundance transcripts, except undef-miR-55 and undef-miR-523, and gender-biased expression was not observed for olfactory-related miRNAs. Our findings provide an overview of the potential miRNAs involved in olfactory regulation, which may provide important information on the function of miRNAs in the insect olfactory system.

Enhancing aphid resistance in horticultural crops: a breeding prospective

Increasing agricultural losses caused by insect infestations are a significant problem, so it is important to generate pest-resistant crop varieties to address this issue. Several reviews have examined aphid-plant interactions from an entomological perspective. However, few have specifically focused on plant resistance mechanisms to aphids and their applications in breeding for aphid resistance. In this review, we first outline the types of resistance to aphids in plants, namely antixenosis, tolerance (cell wall lignification, resistance proteins), and antibiosis, and we discuss strategies based on each of these resistance mechanisms to generate plant varieties with improved resistance. We then outline research on the complex interactions amongst plants, viruses, and aphids, and discuss how aspects of these interactions can be exploited to improve aphid resistance. A deeper understanding of the epigenetic mechanisms related to induced resistance, i.e. the phenomenon where plants become more resistant to a stress they have encountered previously, may allow for its exploitation in breeding for aphid resistance. Wild relatives of crop plants serve as important sources of resistance traits. Genes related to these traits can be introduced into cultivated crop varieties by breeding or genetic modification, and de novo domestication of wild varieties can be used to exploit multiple excellent characteristics, including aphid resistance. Finally, we discuss the use of molecular design breeding, genomic data, and gene editing to generate new aphid-resistant, high-quality crop varieties.

From trade-off to synergy: how nutrient status modulates plant resistance to herbivorous insects?

The principle of the "growth-defense trade-off" governs how plants adjust their growth and defensive strategies in response to external factors, impacting interactions among plants, herbivorous insects, and their natural enemies. Mineral nutrients are crucial in modulating plant growth and development through their bottom-up effects. Emerging evidence has revealed complex regulatory networks that link mineral nutrients to plant defense responses, influencing the delicate balance between growth and defense against herbivores. This review aims to summarize recent advances that elucidate the impact of nutrient availability on plant defense responses. Particularly, we focus on how nutrient status shapes plant resistance to herbivores, delving into the molecular mechanisms underlying this physiological process. Moreover, the interplay between mineral nutrients and various herbivore defense mechanisms, including physical protection, plant hormone signaling, defensive metabolite production, and volatile organic compound emissions that deter herbivores or attract their natural enemies, are discussed. This comprehensive review sets the stage for future investigations into the intricate crosstalk between nutrient signaling and plant defense responses, which serves as a central mechanism to guide sustainable pest management approaches, thereby promoting balanced agroecosystem health and enhancing plant ecosystem productivity and resilience.

Two Structural Analogs of Kairomones are Detected by an Odorant Receptor HvarOR28 in the Coccinellid Hippodamia variegata

In natural environments, general plant volatiles and herbivore-induced plant volatiles (HIPVs) serve as critical clues for predatory natural enemies in the search for prey. The insect olfactory system plays a vital role in perceiving plant volatiles including HIPVs. In this study, we found that HIPV (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT) and the plant volatile geranyl acetate (GA), two structurally similar chemicals, displayed electrophysiological activities on the antennae of the ladybird Hippodamia variegata, but were only attractive to adult females in behavior. Moreover, mated female ladybirds laid a significantly higher number of eggs on TMTT-treated and GA-treated cotton leaves compared to controls. Screening of female-biased odorant receptors (ORs) from the antennal transcriptomes, performing Xenopus oocytes expression coupled with two-electrode voltage clamp recordings, suggested that HvarOR28 specifically tuned to TMTT and GA. Molecular docking and site-directed mutagenesis revealed that the amino acid residues Tyr143 and Phe81 of HvarOR28 are the key site for binding with TMTT and GA. Furthermore, RNA interference (RNAi) assay demonstrated that HvarOR28-silenced individuals demonstrated a notable decrease in electrophysiological responses, even female adults almost lost behavioral preference for the two compounds. Thus, it could be concluded that HvarOR28 in H. variegata contributes to facilitating egg laying through the perception of TMTT and GA. These findings may help to develop new olfactory modulators based on the behaviorally active ligands of HvarOR28.

MCMV-infected maize attracts its insect vector Frankliniella occidentalis by inducing β-myrcene

Maize lethal necrosis is attributed to the accumulation of maize chlorotic mottle virus (MCMV), an invasive virus transmitted by insect vectors. The western flower thrips (WFT) can shift host to maize, thus promoting the spread of MCMV. However, our understanding of the characteristics and interactions involved in the transmission of MCMV is still limited. This study finds that non-viruliferous WFTs showed a 57.56% higher preference for MCMV-infected maize plants compared to healthy maize plants, while viruliferous WFTs showed a 53.70% higher preference for healthy maize plants compared to MCMV-infected maize plants. We also show for the first time that both adults and larvae of WFT could successfully acquire MCMV after 1 min of acquisition access period (AAP), and after 48 h of AAP, WFT could transmit MCMV in an inoculation access period of 1 h without a latent period. Both adults and larvae of WFT can transmit MCMV for up to 2 days. Furthermore, the decreasing number of viruliferous WFTs and transmission rates as time progressed, together with the transcriptomic evidence, collectively suggest that WFTs transmit MCMV in a semi-persistent method, a mode of transmission requiring minutes to several hours for acquisition access and having a retention time of several hours to a few days. Additionally, β-myrcene can attract WFTs significantly and is detected in Nicotiana benthamiana plants transiently expressing MCMV CP (coat protein), which is consistent with results in MCMV-infected maize plants through the metabolomic profiling and the preference analyses of WFT. Therefore, this study demonstrates the indirect interaction between MCMV and WFT by inducing maize to synthesize β-myrcene to attract insect vectors. The exploration of specific interactions between MCMV and WFT could help to expand the mechanism studies of virus-vector-host plant interaction and put forward a new insight for the combined control of MCMV and WFT through the manipulation of plant volatiles and key insect genes.

Synergism of (E)-β-farnesene and Its Analogue to Insecticides against the Green Peach Aphid Myzus persicae

With high aphid-repellent activity but low stability, (E)-β-farnesene (EβF), the major component of the aphid alarm pheromone, can be used as a synergist to insecticides. Some EβF analogues possess both good aphid-repellent activity and stability, but the synergistic effect and related mechanism are still unclear. Therefore, this study investigated the synergistic effect and underlying mechanism of the EβF and its analogue against the aphid Myzus persicae. The results indicated that EβF and the analogue showed significantly synergistic effects to different insecticides, with synergism ratios from 1.524 to 3.446. Mechanistic studies revealed that EβF and the analogue exhibited effective repellent activity, significantly upregulated target OBP genes by 161 to 731%, increased aphid mobility, and thereby enhanced contact with insecticides. This research suggests that the EβF analogue represents a novel synergist for insecticides, with the potential for further application in aphid control owing to its enhanced bioactivity and the possibility of reducing insecticide doses.

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.

Densovirus infection facilitates plant-virus transmission by an aphid

The interactions among plant viruses, insect vectors, and host plants have been well studied; however, the roles of insect viruses in this system have largely been neglected. We investigated the effects of MpnDV infection on aphid and PVY transmission using bioassays, RNA interference (RNAi), and GC-MS methods and green peach aphid (Myzus persicae (Sulzer)), potato virus Y (PVY), and densovirus (Myzus persicae nicotianae densovirus, MpnDV) as model systems. MpnDV increased the activities of its host, promoting population dispersal and leading to significant proliferation in tobacco plants by significantly enhancing the titer of the sesquiterpene (E)-β-farnesene (EβF) via up-regulation of expression levels of the MpFPPS1 gene. The proliferation and dispersal of MpnDV-positive individuals were faster than that of MpnDV-negative individuals in PVY-infected tobacco plants, which promoted the transmission of PVY. These results combined showed that an insect virus may facilitate the transmission of a plant virus by enhancing the locomotor activity and population proliferation of insect vectors. These findings provide novel opportunities for controlling insect vectors and plant viruses, which can be used in the development of novel management strategies.

Two sex pheromone receptors for sexual communication in the American cockroach

Volatile sex pheromones are vital for sexual communication between males and females. Females of the American cockroach, Periplaneta americana, produce and emit two sex pheromone components, periplanone-A (PA) and periplanone-B (PB). Although PB is the major sex attractant and can attract males, how it interacts with PA in regulating sexual behaviors is still unknown. In this study, we found that in male cockroaches, PA counteracted PB attraction. We identified two odorant receptors (ORs), OR53 and OR100, as PB/PA and PA receptors, respectively. OR53 and OR100 were predominantly expressed in the antennae of sexually mature males, and their expression levels were regulated by the sex differentiation pathway and nutrition-responsive signals. Cellular localization of OR53 and OR100 in male antennae further revealed that two types of sensilla coordinate a complex two-pheromone-two-receptor pathway in regulating cockroach sexual behaviors. These findings indicate distinct functions of the two sex pheromone components, identify their receptors and possible regulatory mechanisms underlying the male-specific and age-dependent sexual behaviors, and can guide novel strategies for pest management.

Aphid alarm pheromone mimicry in transgenic Chrysanthemum morifolium: insights into the potential of (E)-β-farnesene for aphid resistance

(E)-β-Farnesene (EBF) serves as the primary component of the alarm pheromone used by most aphid pest species. Pyrethrum (Tanacetum cinerariifolium) exhibits tissue-specific regulation of EBF accumulation and release, effectively mimicking the aphid alarm signal, deterring aphid attacks while attracting aphid predators. However, cultivated chrysanthemum (Chrysanthemum morifolium), a popular and economically significant flower, is highly vulnerable to aphid infestations. In this study, we investigated the high expression of the pyrethrum EBF synthase (TcEbFS) gene promoter in the flower head and stem, particularly in the parenchyma cells. Subsequently, we introduced the TcEbFS gene, under the control of its native promoter, into cultivated chrysanthemum. This genetic modification led to increased EBF accumulation in the flower stem and young flower bud, which are the most susceptible tissues to aphid attacks. Analysis revealed that aphids feeding on transgenic chrysanthemum exhibited prolonged probing times and extended salivation durations during the phloem phase, indicating that EBF in the cortex cells hindered their host-location behavior. Interestingly, the heightened emission of EBF was only observed in transgenic chrysanthemum flowers after mechanical damage. Furthermore, we explored the potential of this transgenic chrysanthemum for aphid resistance by comparing the spatial distribution and storage of terpene volatiles in different organs and tissues of pyrethrum and chrysanthemum. This study provides valuable insights into future trials aiming for a more accurate replication of alarm pheromone release in plants. It highlights the complexities of utilizing EBF for aphid resistance in cultivated chrysanthemum and calls for further investigations to enhance our understanding of this defense mechanism.

Identifying the Key Role of Plutella xylostella General Odorant Binding Protein 2 in Perceiving a Larval Attractant, (E,E)-2,6-Farnesol

There is currently a lack of effective olfaction-based techniques to control diamondback moth (DBM) larvae. Identifying behaviorally active odorants for DBM larvae and exploring their recognition mechanisms can provide insights into olfaction-based larval control strategies. Through the two-choice assay, (E,E)-2,6-farnesol (farnesol) was identified as a compound exhibiting significant attractant activity toward DBM larvae, achieving an attraction index of 0.48 ± 0.13. PxylGOBP1 and PxylGOBP2, highly expressed in the antennae of DBM larvae, both showed high affinity toward farnesol. RNAi technology was used to knock down PxylGOBP1 and PxylGOBP2, revealing that the attraction of DBM larvae to farnesol nearly vanished following the knockdown of PxylGOBP2, indicating its critical role in recognizing farnesol. Further investigation into the PxylGOBP2-farnesol interaction revealed the importance of residues like Thr9, Trp37, and Phe118 in PxylGOBP2's binding to farnesol. This research is significant for unveiling the olfactory mechanisms of DBM larvae and developing larval behavior regulation techniques.

An odorant receptor mediates the avoidance of Plutella xylostella against parasitoid

BACKGROUND

Ecosystems are brimming with myriad compounds, including some at very low concentrations that are indispensable for insect survival and reproduction. Screening strategies for identifying active compounds are typically based on bioassay-guided approaches.

RESULTS

Here, we selected two candidate odorant receptors from a major pest of cruciferous plants-the diamondback moth Plutella xylostella-as targets to screen for active semiochemicals. One of these ORs, PxylOR16, exhibited a specific, sensitive response to heptanal, with both larvae and adult P. xylostella displaying heptanal avoidance behavior. Gene knockout studies based on CRISPR/Cas9 experimentally confirmed that PxylOR16 mediates this avoidance. Intriguingly, rather than being involved in P. xylostella-host plant interaction, we discovered that P. xylostella recognizes heptanal from the cuticular volatiles of the parasitoid wasp Cotesia vestalis, possibly to avoid parasitization.

CONCLUSIONS

Our study thus showcases how the deorphanization of odorant receptors can drive discoveries about their complex functions in mediating insect survival. We also demonstrate that the use of odorant receptors as a screening platform could be efficient in identifying new behavioral regulators for application in pest management.

Behavioral and molecular response of the insect parasitic nematode Steinernema carpocapsae to plant volatiles

Entomopathogenic nematodes (EPNs) use the chemical cues emitted by insects and insect-damaged plants to locate their hosts. Steinernema carpocapsae, a species of EPN, is an established biocontrol agent used against insect pests. Despite its promising potential, the molecular mechanisms underlying its ability to detect plant volatiles remain poorly understood. In this study, we investigated the response of S. carpocapsae infective juveniles (IJs) to 8 different plant volatiles. Among these, carvone was found to be the most attractive volatile compound. To understand the molecular basis of the response of IJs to carvone, we used RNA-Seq technology to identify gene expression changes in response to carvone treatment. Transcriptome analysis revealed 721 differentially expressed genes (DEGs) between carvone-treated and control groups, with 403 genes being significantly upregulated and 318 genes downregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the responsive DEGs to carvone attraction were mainly involved in locomotion, localization, behavior, response to stimulus, and olfactory transduction. We also identified four upregulated genes of chemoreceptor and response to stimulus that were involved in the response of IJs to carvone attraction. Our results provide insights into the potential transcriptional mechanisms underlying the response of S. carpocapsae to carvone, which can be utilized to develop environmentally friendly strategies for attracting EPNs.

Exploring the functional profiles of odorant binding proteins crucial for sensing key odorants in the new leaves of coconut palms in Rhynchophorus ferrugineus

The red palm weevil (RPW), Rhynchophorus ferrugineus (Curculionidae: Coleoptera) is a highly destructive global pest of coconut trees, with a preference for laying its eggs on new leaves. Females can identify where to lay eggs by using their sense of smell to detect specific odorants found in new leaves. In this study, we focused on the two odorants commonly found in new leaves by GC-MS: trans, trans-2,4-nonadienal and trans-2-nonenal. Our behavioral assays demonstrated a significant attraction of females to both of these odorants, with their electrophysiological responses being dose-dependent. Furthermore, we examined the expression patterns induced by these odorants in eleven RferOBP genes. Among them, RferOBP3 and RferOBP1768 exhibited the most significant and simultaneous upregulation. To further understand the role of these two genes, we conducted experiments with females injected with OBP-dsRNA. This resulted in a significant decrease in the expression of RferOBP3 and RferOBP1768, as well as impaired the perception of the two odorants. A fluorescence competitive binding assay also showed that both RferOBPs strongly bound to the odorants. Additionally, sequence analysis revealed that these two RferOBPs belong to the Minus-C family and possess four conserved cysteines. Molecular docking simulations showed strong interactions between these two RferOBPs and the odorant molecules. Overall, our findings highlight the crucial role of RferOBP3 and RferOBP1768 in the olfactory perception of the key odorants in coconut palm new leaves. This knowledge significantly improves our understanding of how RPW females locate sites for oviposition and lays the foundation for future research on the development of environmentally friendly pest attractants.

D-Limonene Affects the Feeding Behavior and the Acquisition and Transmission of Tomato Yellow Leaf Curl Virus by Bemisia tabaci

Bemisia tabaci (Gennadius) is an important invasive pest transmitting plant viruses that are maintained through a plant-insect-plant cycle. Tomato yellow leaf curl virus (TYLCV) can be transmitted in a persistent manner by B. tabaci, which causes great losses to global agricultural production. From an environmentally friendly, sustainable, and efficient point of view, in this study, we explored the function of d-limonene in reducing the acquisition and transmission of TYLCV by B. tabaci as a repellent volatile. D-limonene increased the duration of non-feeding waves and reduced the duration of phloem feeding in non-viruliferous and viruliferous whiteflies by the Electrical Penetration Graph technique (EPG). Additionally, after treatment with d-limonene, the acquisition and transmission rate of TYLCV was reduced. Furthermore, BtabOBP3 was determined as the molecular target for recognizing d-limonene by real-time quantitative PCR (RT-qPCR), fluorescence competitive binding assays, and molecular docking. These results confirmed that d-limonene is an important functional volatile which showed a potential contribution against viral infections with potential implications for developing effective TYLCV control strategies.

Imaging metabolic mechanisms and the binding behavior of nutrients/transporters of edible Matricaria flowers VOCs

To promote the consumption of flowers and to utilize the nutritional value of proteins, the efficacy of the beneficial components of flowers has been intensively studied. Anthemis nobilis was used as the study object, and all its volatile components (VOCs) were fingerprinted using headspace solid-phase micro-extraction gas-mass spectrometry (HS-SPME/GC-MS). GC-MS fingerprints of five parts of Anthemis nobilis were established using three proteins, bovine lactoferrin (BLF), bovine lactoglobulin (β-Lg), and human serum albumin (HSA), as nutrient transporters. The interactions between the volatile components from different parts of the mother chrysanthemum plant and the nutrient/transport proteins were investigated. The results of fingerprinting showed that the flavor components were dominated by alkenes. In addition, this study revealed that among the three nutrient transporters, the strongest binding to the adsorbed volatile components was HSA, followed by BLF, and β-Lg was second. In addition, a characteristic molecule, camphene, was screened. Integrated molecular simulation using fluorescence spectroscopy was used to validate the results of the interaction of the nutrient/transport proteins systems with characteristic molecule. The properties of the characteristic molecules such as absorption, distribution, metabolism, excretion and toxicity in vivo were analyzed using ADMET to provide a theoretical basis for the preparation of flower-flavored dairy products.

Mutagenesis of Odorant Receptor Coreceptor Orco Reveals the Odorant-Detected Behavior of the Predator Eupeodes corollae

The successful mating of the hoverfly and the search for prey aphids are of great significance for biological control and are usually mediated by chemical cues. The odorant receptor co-receptor (Orco) genes play a crucial role in the process of insect odor perception. However, the function of Orco in the mating and prey-seeking behaviors of the hoverfly remains relatively unexplored. In this study, we characterized the Orco gene from the hoverfly, Eupeodes corollae, a natural enemy insect. We used the CRISPR/Cas9 technique to knock out the Orco gene of E. corollae, and the EcorOrco-/- homozygous mutant was verified by the genotype analysis. Fluorescence in situ hybridization showed that the antennal ORN of EcorOrco-/- mutant lack Orco staining. Electroantennogram (EAG) results showed that the adult mutant almost lost the electrophysiological response to 15 odorants from three types. The two-way choice assay and the glass Y-tube olfactometer indicated that both the larvae and adults of hoverflies lost their behavioral preference to the aphid alarm pheromone (E)-β-farnesene (EBF). In addition, the mating assay results showed a significant decrease in the mating rate of males following the knock out of the EcorOrco gene. Although the mating of females was not affected, the amount of eggs being laid and the hatching rate of the eggs were significantly reduced. These results indicated that the EcorOrco gene was not only involved in the detection of semiochemicals in hoverflies but also plays a pivotal role in the development of eggs. In conclusion, our results expand the comprehension of the chemoreceptive mechanisms in the hoverflies and offers valuable insights for the advancement of more sophisticated pest management strategies.

Deciphering the Chemical Fingerprint of Astragalus membranaceus: Volatile Components Attractive to Bruchophagus huonchili Wasps

Bruchophagus huonchili is a pest that poses a serious threat to the yield and quality of Astragalus membranaceus seeds. In this study, we employed solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) to identify volatile organic compounds (VOCs) in A. membranaceus pods during the pod-filled period. Additionally, we utilized a Y-tube olfactometer to measure the behavioral response of B. huonchili to different individual VOCs and specific VOC-based formulations. The most effective formulations were further evaluated for their effectiveness in attracting wasps in the field. Our findings revealed that A. membranaceus pods emit 25 VOCs, including green leaf volatiles (GLVs) and terpenoid and aromatic compounds. Among these compounds, five were found to be most attractive to B. huonchili at the following concentrations: 10 µg/µL cis-β-ocimene, 500 µg/µL hexyl acetate, 100 µg/µL hexanal, 1 µg/µL decanal, and 10 µg/µL β-caryophyllene, with respective response rates of 67.65%, 67.74%, 65.12%, 67.57%, and 66.67%. In addition, we evaluated 26 mixed VOC formulations, and three of them were effective at attracting B. huonchili. Furthermore, field experiments showed that one of the formulations was significantly more effective than the others, which could be used for monitoring B. huonchili populations.

Essential Oils of Artemisia frigida Plants (Asteraceae): Conservatism and Lability of the Composition

Plants of arid regions have adapted to harsh environments during the long span of their evolution and have developed a set of features necessary for their survival in water-limited conditions. Artemisia frigida Willd. (Asteraceae) is a widely distributed species possessing significant cenotic value in steppe ecosystems due to its high frequency and abundance. This study examines different patterns of formation of essential oil composition in A. frigida plants under the influence of heterogeneous factors, including climate and its integral characteristics (HTC, Cextr, SPEI and others). The work is based on the results of our research conducted in Russia (Republic of Buryatia, Irkutsk region), Mongolia, and China, from 1998 to 2021. A total of 32 constant compounds have been identified in the essential oil of A. frigida throughout its habitat range in Eurasia, from Kazakhstan to Qinghai Province, China. Among them, camphor, 1,8-cineol and bornyl acetate are the dominant components, contained in 93-95% of the samples. Among the sesquiterpenoids, germacrene D is the dominant component in 67% of the samples. The largest variability within the composition of the essential oils of A. frigida is associated with significant differences in the climatic parameters when plants grow in high-altitude and extrazonal conditions.

The genome sequence of the Vagrant Hoverfly, Eupeodes corollae (Fabricius, 1794)

We present a genome assembly from an individual female Eupeodes corollae (the Vagrant Hoverfly; Arthropoda; Insecta; Diptera; Syrphidae). The genome sequence is 648.2 megabases in span. Most of the assembly is scaffolded into four chromosomal pseudomolecules, including with the X sex chromosome. The mitochondrial genome has also been assembled and is 18.3 kilobases in length.

Multiple Receptors Contribute to the Attractive Response of Caenorhabditis elegans to Pathogenic Bacteria

Nematodes feed mainly on bacteria and sense volatile signals through their chemosensory system to distinguish food from pathogens. Although nematodes recognizing bacteria by volatile metabolites are ubiquitous, little is known of the associated molecular mechanism. Here, we show that the antinematode bacterium Paenibacillus polymyxa KM2501-1 exhibits an attractive effect on Caenorhabditis elegans via volatile metabolites, of which furfural acetone (FAc) acts as a broad-spectrum nematode attractant. We show that the attractive response toward FAc requires both the G-protein-coupled receptors STR-2 in AWC neurons and SRA-13 in AWA and AWC neurons. In the downstream olfactory signaling cascades, both the transient receptor potential vanilloid channel and the cyclic nucleotide-gated channel are necessary for FAc sensation. These results indicate that multiple receptors and subsequent signaling cascades contribute to the attractive response of C. elegans to FAc, and FAc is the first reported ligand of SRA-13. Our current work discovers that P. polymyxa KM2501-1 exhibits an attractive effect on nematodes by secreting volatile metabolites, especially FAc and 2-heptanone, broadening our understanding of the interactions between bacterial pathogens and nematodes. IMPORTANCE Nematodes feed on nontoxic bacteria as a food resource and avoid toxic bacteria; they distinguish them through their volatile metabolites. However, the mechanism of how nematodes recognize bacteria by volatile metabolites is not fully understood. Here, the antinematode bacterium Paenibacillus polymyxa KM2501-1 is found to exhibit an attractive effect on Caenorhabditis elegans via volatile metabolites, including FAc. We further reveal that the attractive response of C. elegans toward FAc requires multiple G-protein-coupled receptors and downstream olfactory signaling cascades in AWA and AWC neurons. This study highlights the important role of volatile metabolites in the interaction between nematodes and bacteria and confirms that multiple G-protein-coupled receptors on different olfactory neurons of C. elegans can jointly sense bacterial volatile signals.

Conserved Odorant Receptor, EcorOR4, Mediates Attraction of Mated Female Eupeodes corollae to 1-Octen-3-ol

Odorant receptors (ORs) in insects are crucial for the detection of chemical signals. However, the functions of the conserved OR genes among insect species are rarely studied. In this study, we analyzed a well-conserved OR clade in Diptera insects and cloned a gene from this clade, EcorOR4, in the hoverfly Eupeodes corollae. Real-time quantitative PCR showed that EcorOR4 was highly expressed in the antennae and upregulated in the mated females, and in vitro functional characterization showed that EcorOR4 was narrowly tuned to 1-octen-3-ol. Electroantennogram assays revealed that the antennal response of mated females to 1-octen-3-ol was significantly higher than that of mated males, but no significant differences were observed between male and female virgins. Finally, a Y-tube olfactometer bioassay showed that 1-octen-3-ol is an attractant for only mated female E. corollae adults. These results demonstrate that EcorOR4 is involved in the detection of 1-octen-3-ol and that this compound may affect the host-finding and oviposition behavior in female E. corollae.

Functional analysis of odorant-binding proteins for the parasitic host location to implicate convergent evolution between the grain aphid and its parasitoid Aphidius gifuensis

(E)-β-farnesene (EBF) is a typical and ecologically important infochemical in tri-trophic level interactions among plant-aphid-natural enemies. However, the molecular mechanisms by which parasitoids recognize and utilize EBF are unclear. In this study, we functionally characterized 8 AgifOBPs in Aphidifus gifuensis, one dominant endo-parasitoid of wheat aphid as well as peach aphid in China. Among which, AgifOBP6 was the only OBP upregulated by various doses of EBF, and it showed a strong binding affinity to EBF in vitro. The lack of homology between AgifOBP6 and EBF-binding proteins from aphids or from other aphid natural enemies supported that this was a convergent evolution among insects from different orders driven by EBF. Molecular docking of AgifOBP6 with EBF revealed key interacting residues and hydrophobic forces as the main forces. AgifOBP6 is widely expressed among various antennal sensilla. Furthermore, two bioassays indicated that trace EBF may promote the biological control efficiency of A. gifuensis, especially on winged aphids. In summary, this study reveals an OBP (AgifOBP6) that may play a leading role in aphid alarm pheromone detection by parasitoids and offers a new perspective on aphid biological control by using EBF. These results will improve our understanding of tri-trophic level interactions among plant-aphid-natural enemies.

Odorant-Binding Protein HvarOBP5 in Ladybird Hippodamia variegata Regulates the Perception of Semiochemicals from Preys and Habitat Plants

A total of 12 OBPs were identified in the antennae of ladybird Hippodamia variegata. HvarOBP1/2/5/6/10/11 were highly expressed in adults, whereas HvarOBP3/4/7/8/9/12 had higher expression levels in larvae. In adults, HvarOBP1/2/4/5/6/7/8/11/12 were highly expressed in antennae. Among these, recombinant HvarOBP5 strong bound with (E)-β-farnesene (EβF), (R)-(+)-limonene, (E,E)-4,8,12-trimethyltrideca-l,3,7,11-tetraene (TMTT), (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), hexyl hexanoate, and geranyl acetate. Molecular docking indicated that Leu42, Lys43, and His64 were the key binding sites of HvarOBP5. All six ligands evoked electroantennography (EAG) responses in ladybirds. Moreover, (R)-(+)-limonene and hexyl hexanoate were attractive to both sexes. After RNA interference for 72 h, the EAGs of dsRNA-injected ladybirds to DMNT and hexyl hexanoate were significantly decreased by 73.8 and 78.6%, respectively. Both dsRNA-injected males and females showed significantly lower behavioral preferences for DMNT and hexyl hexanoate. These findings suggest that HvarOBP5 in H. variegata plays an important role in the perception of semiochemical cues from preys and habitat plants.

Plants strike back: Plant volatiles and their role in indirect defence against aphids

As sessile organisms, plants have evolved different strategies to defend themselves against various biotic stressors. An important aspect of the complex response of plants to biotic stress is the emission of volatile compounds (VOCs), which are involved in direct and indirect plant defence mechanisms. Indirect plant defences include a range of plant traits that mediate defence against herbivores and play an important ecological role by not only utilising plants' own capabilities, but also signalling and attracting natural enemies of herbivores. Often the combination of volatiles emitted is specific to herbivores; they are consequently recognised by parasites and other predators, providing a clear link between the volatile signature and the prey. In this review, we focus on indirect plant defence and summarise current knowledge and perspectives on relationships between plants, aphids and parasitic wasps.

Comparative morphology and plant volatile responses of antennal sensilla in Cinara cedri (Hemiptera: Lachninae), Eriosoma lanigerum (Hemiptera: Eriosomatinae), and Therioaphis trifolii (Hemiptera: Calaphidinae)

Olfaction is important for mediating aphid behaviors and is involved in host location and mating. Antennal primary rhinaria play a key role in the chemoreception of aphids. The function of the peripheral olfactory system in the subfamily Aphidinae has been intensively studied, but little is known about other subfamilies of Aphididae. Therefore, three aphid species were selected to study the olfactory reception of plant volatiles: Cinara cedri (Lachninae), Eriosoma lanigerum (Eriosomatinae), and Therioaphis trifolii (Calaphidinae). In this study, the morphology and distribution of the antennal sensilla of apterous adults were observed by scanning electron microscopy. Three morphological types were identified (placoid sensilla, coeloconic sensilla, and trichoid sensilla); the first two were distributed on the antennal primary rhinaria. A pattern of primary rhinaria in C. cedri was found that differed from that of E. lanigerum and T. trifolii and consists of 1 large placoid sensillum (LP) on the 4th segment, 2 LPs on the 5th segment, and a group of sensilla on the 6th antennal segments. Later, we recorded and compared neuronal responses of the distinct placoid sensilla in the primary rhinaria of the three aphid species to 18 plant volatiles using a single sensillum recording (SSR) technique. The results indicated that the functional profiles based on the tested odorants of the primary rhinaria of the three investigated aphid species were clustered into three classes, and exhibited excitatory responses to certain types of odorants, especially terpenes. In C. cedri, the ORNs in LP6 exhibited the highest responses to (±)-citronellal across all tested chemicals, and showed greater sensitivity to (±)-citronellal than to (+)-limonene. ORNs in LP5 were partially responsive to α-pinene and (-)-β-pinene in a dose-dependent manner. Across different species, E. lanigerum showed significantly stronger neuronal responses of LP5 to several terpenes, such as (-)-linalool and α-terpineol, compared to other species. In T. trifolii, the neuronal activities in LP6 showed a greater response to methyl salicylate as compared to LP5. Overall, our results preliminarily illustrate the functional divergence of ORNs in the primary rhinaria of aphids from three subfamilies of Aphididae and provide a basis for better understanding the mechanism of olfactory recognition in aphids.

Chemical Composition of Essential Oils of Seven Polygonum Species from Turkey: A Chemotaxonomic Approach

Medicinal plants and herbal preparations are gaining attention in the scientific community today, as they are often used intermittently in the treatment of various diseases. The genus of Polygonum (Polygonaceae), known locally as “madimak”, is an aromatic plant widely used in world flavors. The chemical composition of the essential oils of dried aerial parts of seven of Polygonum was analyzed by GC-MS. These species are Polygonum lapathifolium L., Polygonum persicaria L., Polygonum arenastrum Bor., Polygonum bellardii All., Polygonum arenarium Waldst. Et Kit., Polygonum aviculare L., and Polygonum cognatum Meissn. Qualitative and quantitative differences were found in the essential oil analysis of the seven Polygonum species. The major compounds were determined as (E)-β-farnesene (19. 46%), dodecanal (15.92%), β-caryophyllene (12.95%), in P. aviculare; (E)-β-farnesene (25.00%), dodecanal (20.45%), β-caryophyllene (9.38%), and caryophyllene oxide (8. 26%) in P. persicaria; dodecanal (25.65%), caryophyllene oxide (13.35%), β-caryophyllene (7.95%), and (E)-β-farnesene (6.20%) in P. lapathifolium, and dodecanal (19.65%), (E)-β-farnesene (13.86%), β-caryophyllene (8.06%), and α-terpineol (7.2%) in P. arenarium, dodecanal (16.23%), β-caryophyllene (16.09%), (E)-β-farnesene (12.26%), caryophyllene oxide (7.94%) in P. bellardii, (E)-β-farnesene (20.75%), dodecanal (17.96%), β-caryophyllene (13.01%), α-terpineol (4.97%) in P. arenastrum, (E)-β-farnesene (9.49%), dodecanal (14.01%), β-caryophyllene (11.92%), geranyl acetate (9.49%), and undecanal (7.35%) in P. cognatum. This study is the most comprehensive study conducted to determine the essential oil components of Polygonum species. In addition, a literature review on the composition of the essential oils of these Polygonum taxa was performed. The essential oil components of the species in our study were revealed for the first time with this study.

Binding properties of odorant-binding protein 4 from bean bug Riptortus pedestris to soybean volatiles

The bean bug Riptortus pedestris is a notorious insect pest that can damage various crops, especially soybean, in East Asia. In insects, the olfactory system plays a crucial role in host finding and feeding behaviour in which the odorant-binding proteins (OBPs) are believed to be involved in initial step in this system. In this study, we produced the R. pedestris adult antennae-expressed RpedOBP4 protein using a recombinant expression system in E. coli. Fluorescence competitive binding confirmed that RpedOBP4 has binding affinities to 7 of 20 soybean volatiles (ligands), and that a neutral condition is the best environment for it. The binding property of RpedOBP4 to these ligands was further revealed by integrating data from molecular docking, site-directed mutagenesis and ligand binding assays. This demonstrated that five amino acid residues (I30, L33, Y47, I57 and Y121) are involved in the binding process of RpedOBP4 to corresponding ligands. These findings will not only help us to more thoroughly explore the olfactory mechanism of R. pedestris during feeding on soybean, but also lead to the identification of key candidate targets for developing environmental and efficient behaviour inhibitors to prevent population expansion of R. pedestris in the future.

Kairomonal Effect of Aphid Alarm Pheromones and Analogs on the Parasitoid Diaeretiella rapae

Aphid alarm pheromones, as important semiochemicals, not only mediate behavioral response of aphids, but can also act as kairomones to attract their natural enemies. The sesquiterpene (E)-β-farnesene (EβF), the major alarm pheromone component of most aphid species, has been shown to have a kairomonal effect on the predators of aphids, but other alarm pheromone components, especially the monoterpenes and analogs, are rarely investigated. Here, two EβF analogs were successfully synthesized via the nucleophilic substitution reaction, and we then examined the kairomonal effects of four alarm pheromone components and two EβF analogs on the aphid parasitoid, Diaeretiella rapae. In olfactory bioassays, D. rapae females generally showed no significant behavioral response to these alarm pheromone components and analogs under low concentrations (0.1 μg/μL). Nevertheless, their olfactory response to these compounds gradually enhanced with increasing concentrations. Among the four pheromone components, EβF showed the highest attractive activity, but the parasitoid preferred blends over single compounds. Moreover, the response time decreased as the concentration increased. We confirmed the kairomonal effect of monoterpene alarm pheromone components and their blends, in addition to EβF, on the natural enemies of aphids. This is the first report that the blend of alarm pheromone components and their analogs has a stronger kairomonal effect than do the single components on the natural enemies of aphids. This study contributes to our understanding of the mechanisms involved in the regulation of parasitoid behaviors by kairomones and provides a promising opportunity for designing kairomones for the aphid parasitoid to mediate aphid populations in the field.

Comparison and Functional Analysis of Odorant-Binding Proteins and Chemosensory Proteins in Two Closely Related Thrips Species, Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) Based on Antennal Transcriptome Analysis

Two closely related thrips species, Frankliniella occidentalis and Frankliniella intonsa, are important pests on agricultural and horticultural crops. They have several similarities, including occurrence patterns, host range, and aggregation pheromone compounds. However, there are very few reports about the chemosensory genes and olfactory mechanisms in these two species. To expand our knowledge of the thrips chemosensory system, we conducted antennal transcriptome analysis of two thrips species, and identified seven odorant-binding proteins (OBPs) and eight chemosensory proteins (CSPs) in F. occidentalis, as well as six OBPs and six CSPs in F. intonsa. OBPs and CSPs showed high sequence identity between the two thrips species. The RT-qPCR results showed that the orthologous genes FoccOBP1/3/4/5/6, FintOBP1/3/4/6, FoccCSP1/2/3, and FintCSP1/2 were highly expressed in male adults. Molecular docking results suggested that orthologous pairs FoccOBP4/FintOBP4, FoccOBP6/FintOBP6, and FoccCSP2/FintCSP2 might be involved in transporting the major aggregation pheromone compound neryl (S)-2-methylbutanoate, while orthologous pairs FoccOBP6/FintOBP6, FoccCSP2/FintCSP2, and FoccCSP3/FintCSP3 might be involved in transporting the minor aggregation pheromone compound (R)-lavandulyl acetate. These results will provide a fundamental basis for understanding the molecular mechanisms of pheromone reception in the two thrips species.

An odorant binding protein is involved in counteracting detection-avoidance and Toll-pathway innate immunity

INTRODUCTION

Odorant-binding proteins (OBPs) are a class of small molecular weight soluble proteins that exist as expanded gene families in all insects, acting as ligand carriers mediating olfaction and other physiological processes. During fungal infection, a subset of insect OBPs were shown to be differentially expressed.

OBJECTIVES

We tested whether the altered expression of insect OBPs during pathogenic infection plays a role in behavioral or immune interactions between insect hosts and their pathogens.

METHODS

A wide range of techniques including RNAi-directed knockdown, heterologous protein expression, electrophysiological/behavioral analyses, transcriptomics, gut microbiome analyses, coupled with tandem mass spectrometry ion monitoring, were used to characterize the function of a locust OBP in host behavioral and immune responses.

RESULTS

The entomopathogenic fungus Metarhizium anisopliae produces the volatile compound phenylethyl alcohol (PEA) that causes behavioral avoidance in locusts. This is mediated by the locust odorant binding protein 11 (LmOBP11). Expression of LmOBP11 is induced by M. anisopliae infection and PEA treatment. LmOBP11 participates in insect detection of the fungal-produced PEA and avoidance of PEA-contaminated food, but the upregulation of LmOBP11 upon M. anisopliae infection negatively affects the insect immune responses to ultimately benefit successful mycosis by the pathogen. RNAi knockdown of LmOBP11 increases the production of antimicrobial peptides and enhances locust resistance to M. anisopliae infection, while reducing host antennal electrophysiological responses to PEA and locust avoidance of PEA treated food. Also, transcriptomic and gut microbiome analyses reveal microbiome dysbiosis and changes in host genes involved in behavior and immunity. These results are consistent with the elevated expression of LmOBP11 leading to enhanced volatile detection and suppression of immune responses.

CONCLUSION

These findings suggest a crosstalk between olfaction and immunity, indicating manipulation of host OBPs as a novel target exploited by fungal pathogens to alter immune activation and thus promote the successful infection of the host.

The main component of the aphid alarm pheromone (E)-β-farnesene affects the growth and development of Spodoptera exigua by mediating juvenile hormone-related genes

The (E)-β-farnesene (EβF) is one of the most important secondary metabolites in some plants and provides indirect defense against aphids. However, the direct effect of EβF against pests is still unclear. In this study, various concentrations of EβF (0.16, 0.8, and 4 g/kg) were provided in an artificial diet to determine the direct effects of EβF on Spodoptera exigua. The results showed that an artificial diet containing 4 g/kg of EβF reduced the final survival of the S. exigua larvae and per female fecundity of adults significantly when compared with CK and SC controls (p < 0.05), then ultimately it also significantly affected the intrinsic rate of increase (p < 0.05). Furthermore, the results of the EβF bioassay in an artificial diet also indicated that the proliferation of the S. exigua population was inhibited by the ingestion of EβF in a dose-dependent manner. Combined differential RNA-seq data and RT-qPCR analysis, it was found that four key genes involved in juvenile hormone degradation significantly upregulated in S. exigua larvae treated by EβF at a dose of 0.8 and 4 g/kg when compared with two controls (p < 0.05). This indicated that EβF could disturb the normal function of juvenile hormones and reduce the survival rate of S. exigua larvae. Additionally, two key genes that regulate per fecundity of S. exigua females, including SeVg and SeVgR, were significantly downregulated in adult females (p < 0.05) when they were treated with 0.8 and 4 g/kg of EβF at the larval stage, relative to the expression of these genes after treatment with controls. These findings suggested that EβF first disturbed the normal function of juvenile hormone by upregulating key degradation genes, and then inhibited the expression of SeVg/SeVgR genes and proteins, thus reducing the population size of S. exigua by increasing larval mortality and inhibiting per female fecundity.

Genome-wide transcriptomic changes reveal the genetic pathways involved in insect migration

Insects are capable of extraordinary feats of long-distance movement that have profound impacts on the function of terrestrial ecosystems. The ability to undertake these movements arose multiple times through the evolution of a suite of traits that make up the migratory syndrome, however the underlying genetic pathways involved remain poorly understood. Migratory hoverflies (Diptera: Syrphidae) are an emerging model group for studies of migration. They undertake seasonal movements in huge numbers across large parts of the globe and are important pollinators, biological control agents and decomposers. Here, we assembled a high-quality draft genome of the marmalade hoverfly (Episyrphus balteatus). We leveraged this genomic resource to undertake a genome-wide transcriptomic comparison of actively migrating Episyrphus, captured from a high mountain pass as they flew south to overwinter, with the transcriptomes of summer forms which were non-migratory. We identified 1543 genes with very strong evidence for differential expression. Interrogation of this gene set reveals a remarkable range of roles in metabolism, muscle structure and function, hormonal regulation, immunity, stress resistance, flight and feeding behaviour, longevity, reproductive diapause and sensory perception. These features of the migrant phenotype have arisen by the integration and modification of pathways such as insulin signalling for diapause and longevity, JAK/SAT for immunity, and those leading to octopamine production and fuelling to boost flight capabilities. Our results provide a powerful genomic resource for future research, and paint a comprehensive picture of global expression changes in an actively migrating insect, identifying key genomic components involved in this important life-history strategy.

Mutualism promotes insect fitness by fungal nutrient compensation and facilitates fungus propagation by mediating insect oviposition preference

Penicillium and Bactrocera dorsalis (oriental fruit fly, Hendel) are major pathogens and pests of citrus fruits, as both of them can cause detrimental losses in citrus production. However, their interaction in the cohabitation of citrus fruits remains elusive. In this study, we revealed a mutualistic relationship between Penicillium and B. dorsalis. We found that insect behaviors can facilitate the entry of fungal pathogens into fruits, and fungal pathogens promote the fitness of insects in return. More specifically, Penicillium could take advantage of the openings left by ovipositors of flies, and adult flies contaminated with Penicillium could spread the fungus to new sites. Moreover, the volatile emissions from fungi could attract gravid flies to the infected site for egg laying. The fungus and B. dorsalis were able to establish mutual interaction, as revealed by the presence of Penicillium DNA in intestinal tracts of flies throughout all larval stages. The fungal partner seemed to promote the emergence rate and shorten the emergence duration of the flies by providing pyridoxine, one of the B group vitamins. Different from previously reported scenarios of strong avoidance of Drosophila and attraction of Aedes aegypti toward Penicillium, our findings unveil a hitherto new paradigm of the mutualism between Penicillium and B. dorsalis, by which both insect and fungus earn benefits to facilitate their propagation.

Neutrophil Immunomodulatory Activity of Farnesene, a Component of Artemisia dracunculus Essential Oils

Despite their reported therapeutic properties, not much is known about the immunomodulatory activity of essential oils present in Artemisia species. We isolated essential oils from the flowers and leaves of five Artemisia species: A. tridentata, A. ludoviciana, A. dracunculus, A. frigida, and A. cana. The chemical composition of the Artemisia essential oil samples had similarities and differences as compared to those previously reported in the literature. The main components of essential oils obtained from A. tridentata, A. ludoviciana, A. frigida, and A. cana were camphor (23.0-51.3%), 1,8-cineole (5.7-30.0%), camphene (1.6-7.7%), borneol (2.3-14.6%), artemisiole (1.2-7.5%), terpinen-4-ol (2.0-6.9%), α-pinene (0.8-3.9%), and santolinatriene (0.7-3.5%). Essential oils from A. dracunculus were enriched in methyl chavicol (38.8-42.9%), methyl eugenol (26.1-26.4%), terpinolene (5.5-8.8%), (E/Z)-β-ocimene (7.3-16.0%), β-phellandrene (1.3-2.2%), p-cymen-8-ol (0.9-2.3%), and xanthoxylin (1.2-2.2%). A comparison across species also demonstrated that some compounds were present in only one Artemisia species. Although Artemisia essential oils were weak activators of human neutrophils, they were relatively more potent in inhibiting subsequent neutrophil Ca2+ mobilization with N-formyl peptide receptor 1 (FPR1) agonist fMLF- and FPR2 agonist WKYMVM, with the most potent being essential oils from A. dracunculus. Further analysis of unique compounds found in A. dracunculus showed that farnesene, a compound with a similar hydrocarbon structure as lipoxin A4, inhibited Ca2+ influx induced in human neutrophils by fMLF (IC50 = 1.2 μM), WKYMVM (IC50 = 1.4 μM), or interleukin 8 (IC50 = 2.6 μM). Pretreatment with A. dracunculus essential oils and farnesene also inhibited human neutrophil chemotaxis induced by fMLF, suggesting these treatments down-regulated human neutrophil responses to inflammatory chemoattractants. Thus, our studies have identified farnesene as a potential anti-inflammatory modulator of human neutrophils.

Spatial Expression Analysis of Odorant Binding Proteins in Both Sexes of the Aphid Parasitoid Aphidius gifuensis and Their Ligand Binding Properties

In China, Aphidius gifuensis is one of the most common endoparasitoids of the green peach aphid Myzus persicae and grain aphid Sitobion miscanthi in the field. Insect odorant-binding proteins (OBPs) play vital roles in odor perception during feeding, host searching, mating and oviposition. In addition, some OBPs are involved in other physiological processes such as gustation and reproduction. In the present study, a comparative antennal transcriptomic analysis was applied between male and female A. gifuensis. The spatial expression patterns among antennae, heads, thoraxes, abdomens and legs of OBPs in both sexes were further profiled. Fifteen AgifOBPs were predicted, and 14 of them were identified by gene cloning, including 12 classic OBPs and 2 min-C OBPs. As expected, all OBPs were mainly expressed at high levels in antennae, heads or legs which are sensory organs and tissues. Finally, ligand binding properties of 2 OBPs (AgifOBP7 and AgifOBP9) were further evaluated. Female leg specifically expressed AgifOBP9 displays a broad and high binding property to aphid alarm pheromones, plant green volatiles and aphid sex pheromones (Ki < 10 μΜ). However, female leg specifically expressed AgifOBP7 displays poor affinity for all tested ligands except CAU-II-11 ((E)-3,7-dimethylocta-2,6-dien-1-yl-2-hydroxy-3-methoxybenzoate), a reported (E)-β-farnesene (EBF) analog with an exceptionally high binding affinity (Ki = 1.07 ± 0.08 μΜ). In summary, we reported the spatial expression pattern of the OBP repertoire in A. gifuensis, and further studied the binding properties of OBP7 and OBP9, which are mainly expressed in female legs, laying the foundation for the dissection of the contribution of OBPs to chemosensation in A. gifuensis.