Odorant reception in insects: roles of receptors, binding proteins, and degrading enzymes

Impacts of neonicotinoid compounds on the structure and function of Apis mellifera OBP14: Insights from SPR, ITC, multispectroscopy, and molecular modeling

Honeybees are vital for biodiversity and agricultural productivity, yet their populations are declining globally, partly due to exposure to neonicotinoid pesticides. Odorant-binding protein 14 (OBP14) plays an important role in honeybee chemosensation, but its involvement in neonicotinoid toxicity remains underexplored due to limitations in traditional fluorescence spectroscopy techniques. This gap hampers our understanding of neonicotinoid risks to honeybee health. Here, we explored the molecular interactions between OBP14 from Apis mellifera and three widely used neonicotinoids (imidacloprid, thiamethoxam, and clothianidin) using molecular modeling, surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), and multispectroscopy. SPR and ITC characterized the binding affinity, specificity, and thermodynamic parameters of AmelOBP14 interacting with three neonicotinoid compounds, revealing that the binding process is spontaneous and primarily driven by hydrophobic and electrostatic interactions. Molecular modeling highlighted that phenylalanine residue Phe54, near the binding site, plays a critical role in these interactions. UV-vis absorption spectroscopy and synchronous fluorescence spectroscopy (SFS) support slight changes in the microenvironment around the aromatic amino acids of OBP14. Fourier Transform Infrared Spectroscopy (FTIR) and circular dichroism spectroscopy (CD) indicate a decrease in the α-helix content of OBP14, suggesting a change in its secondary structure, while three-dimensional (3D) fluorescence spectroscopy confirms the non-fluorescent nature of the OBP14 polypeptide backbone. The study results revealed its potential as a biomarker for pesticide risk assessment, providing important insights into the molecular mechanisms by which neonicotinoids may impair bee chemosensory function, and offering guidance for the design of safer pesticides to minimize harm to these important pollinators.

Expression and sex pheromone-binding characteristics of pheromone-binding protein 3 in Tuta absoluta (Lepidoptera: Gelechiidae)

The olfactory system plays a crucial role in insect survival and reproduction. Odorant-binding proteins (OBPs) are essential for odor discrimination and hold the potential to be targets for pest management. Tuta absoluta (Lepidoptera: Gelechiidae), a devastating invasive pest of Solanaceae crops, has limited research on its OBPs. In this study, 34 OBP genes were identified in T. absoluta, including TabsGOBP1, TabsGOBP2, TabsPBP1a, TabsPBP1b, TabsPBP1c, and TabsPBP3, which belong to the Lepidoptera-specific GOBP/PBP subclass. Expression profiling revealed TabsPBP3 to be predominantly expressed in male antennae and the female pheromone gland-ovipositor complex, with peak expression at 6:00 AM associated with courtship and mating behavior. Fluorescence competitive binding assays demonstrated that TabsPBP3 strongly binds to the main pheromone component (3E, 8Z, 11Z)-tetradecatrien-1-yl acetate (TDTA) but exhibits weak or no affinity for other components. Molecular docking identified key active sites in TabsPBP3, including Phe37, Tyr61, Ile77, Leu84, Ile86, Leu87, Phe101, Ala136, Ile139, and Ala140, which facilitate interaction with TDTA. These findings establish TabsPBP3 as a key player in TDTA detection and provide foundational data for innovative pest control strategies targeting T. absoluta.

Molecular mechanisms based on peripheral level of vanillin recognition in Orthaga achatina (Lepidoptera: Pyralidae)

Orthaga achatina (Lepidoptera Pyralidae) is a specialist pest of the camphor tree Cinnamomum camphora. Vanillin is a volatile compound found in many plants, and its effects on insects can be either attractive or repellent, depending on the species. However, the behavioral response of Orthaga achatina to vanillin, a volatile compound emitted by camphor trees, remains unexplored. In this study, we found that vanillin attracts both male and female O. achatina adults. Fluorescence competitive binding assays further revealed that among the five odorant-binding proteins (OBPs) highly expressed in both male and female antennae, OachOBP7 exhibited the most prominent binding affinity with vanillin. Furthermore, by employing the Xenopus oocyte expression and two-electrode voltage clamp recording system (XOE-TEVC) to conduct a functional characterization of 40 ORs, vanillin was the optimal ligand for OachOR7 among all tested ligands. In addition, with the 3D structure modeling and molecular docking techniques, it was revealed that OachOR7 displayed a relatively high binding affinity (-5.5 kcal/mol), and Gln84 and Asn189 were predicted to be key amino acid residues for binding vanillin. Finally, the two amino acids were verified by site-specific mutagenesis followed by XOE-TEVC, showing that the binding ability of OR7 to vanillin was significantly reduced to 9.23 × 10-2 μM after the mutation of two amino acids. This study demonstrate vanillin's behavioral attraction to O. achatina and reveal its molecular basis, offering new possibilities for targeted pest management using this compound.

BdorOBP32 Perceiving β-Caryophyllene: A Molecular Target for Female Attractant Development in Bactrocera dorsalis

Bactrocera dorsalis is a destructive agricultural pest that attacks over 600 plant species. β-Caryophyllene is considered a potential compound for developing novel female attractants due to its attraction to B. dorsalis females. However, the unknown perception mechanism of β-caryophyllene has been the bottleneck of this process. Odorant binding proteins (OBPs) function to bind odorants and transport them to olfactory receptors. Here, behavioral assays revealed that β-caryophyllene strongly attracted mated, instead of virgin females. RT-qPCR confirmed BdorOBP32 up-regulation out of five OBPs in mated females compared to virgin females. Microscale thermophoresis (MST) results showed BdorOBP32 bind β-caryophyllene with relatively high affinity. Subsequently, CRISPR/Cas9 knockout of BdorOBP32 reduced electroantennograms responses and behavioral preferences to β-caryophyllene in mutants. Moreover, molecular docking and behavioral analysis identified a novel female attractant (α-angelica lactone) targeting BdorOBP32. These findings highlight BdorOBP32 plays critical roles in β-caryophyllene perception and offer new insights for developing novel olfactory behavior modulators.

Impact of elevated CO2 level and egg quiescence duration on gene expression in the peripheral olfactory system of Aedes aegypti

Elevation in CO2 can significantly impact the biology of various organisms, affecting life-history traits of both aquatic and terrestrial forms, including disease-vectoring mosquitoes. For mosquitoes, this effect is accentuated by egg quiescence duration, resulting in a change in foraging of adult females. Female mosquitoes rely on their olfactory system for locating resources, such as nectar and blood. This study employs a transcriptomic approach to investigate how a projected elevation in CO2 level, under a worst-case scenario, interacts with extended egg quiescence duration to modulate the molecular machinery of the peripheral olfactory system, the antennae and maxillary palps, of the yellow fever mosquito, Aedes aegypti. The transcriptome analysis demonstrates significant changes in the abundance of genes related to metabolism, xenobiotics degradation and chemosensory function, with the most pronounced effects observed in the CO2 sensing tissue, the maxillary palp. The study provides novel insights into how anthropogenic climate change can modulate the olfactory sensory system of disease vectors, which may have cascading effects on resource-seeking behaviour.

BmMed6 modulates mating behavior by ORs and antennae structural genes in the silkworm

Gene expression is under strict and precise control to regulate organism development and maintain various physiological functions. The Mediator complex is a regulator of gene transcription. Our study focused on BmMed6, a component of the Mediator complex in the Bombyx mori. We construct BmMed6 mutants using the CRISPR-Cas9 system. The mutants exhibited abnormal growth patterns in their antennae, which limited their mating behavior. RNA-seq and gene expression analysis have revealed that the expression of genes associated with structural constituents of the cuticle in the antennae of the mutant was aberrant. Moreover, the deficiency of BmMed6 also caused the downregulation of olfactory receptor genes. Our findings offer novel insights into the biological role of BmMed6 in antenna growth, revealing its crucial role in regulating antenna structure and olfactory gene expression to influence mating behaviors. This discovery identifies BmMed6 as a viable new target gene for pest control.

A Dual RNA-Seq Analysis Revealed Dynamic Arms Race during the Infestation of Wheat by the English Grain Aphid (Sitobion avenae)

Sitobion avenae is an important pest that threatens the safety of wheat production in China. However, the resistance mechanisms of wheat to S. avenae are not well understood at present. In this study, we investigated the mechanisms of interaction between wheat and S. avenae at four infestation time points (6, 24, 48, and 72 hpi) using a high-resolution time series dual transcriptomic analysis. The results showed that plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis pathways were significantly activated in the wheat spike of Lunxuan144 during S. avenae infestation. Meanwhile, the functional analysis of the S. avenae transcriptome revealed that some secretory proteins participated in wheat-S. avenae interaction. This study sheds light on the arms race process between S. avenae and wheat, laying the foundation for the green prevention of S. avenae and providing a theoretical basis for mining the key functional genes in both wheat and S. avenae.

In vitro larvicidal activity of selected azabenzimidazole and diarylquinoline derivatives against Anopheles gambiae and in silico mechanistic analysis

Different species of mosquitoes are responsible for transmitting infectious diseases such as chikungunya, dengue, Japanese encephalitis, lymphatic filariasis, rift valley fever, west nile fever, yellow fever, zika virus, and malaria. Particularly, malaria infection is endemic in sub-Saharan Africa region, and female anopheles mosquitoes is responsible for the transmission of the parasite causing the infection. The growing resistance of mosquitoes to conventional insecticides and the need to complement existing strategies for the elimination of malaria transmission necessitate the exploration of alternative vector control strategies. In this study, we investigated the in vitro larvicidal potential of three examples of diarylquinoline and two examples of azabenzimidazole derivatives against the fourth instar larvae of Anopheles gambiae. The compounds were also evaluated in silico, specifically targeting odorant-binding proteins (OBPs) of An. gambiae and Culex quinquefasciatus. The larvicidal assay indicated that three of the compounds exhibited significant bioactivity, with LC50 below 20 µg/ml after 48 h. Molecular docking and dynamics simulations further elucidated the binding interactions between the active compounds and the selected OBPs, revealing high binding affinities and stable protein-ligand complexes. These findings suggest that two of the tested compounds have promising potential for optimization into larvicidal agents with OBPs inhibitory potential while complimenting existing mosquito control tools.

Coordinated mediation of the response to ethyl linoleate by two odorant-binding proteins in Plodia interpunctella larvae

The Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae), is a ubiquitous pest in stored products, with the larvae inflicting the most damage. The molecular mechanisms underlying larval olfaction and associated behaviors remain poorly understood. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis revealed two odorant binding proteins of P. interpunctella (PintOBPs) with antenna-biased expression in larvae. Competitive binding assays revealed that both PintOBP18 and PintOBP19 bind to a variety of volatile compounds emitted from stored food products, with ethyl linoleate identified as the best ligand for both proteins. According to RNA interference tests, the attractiveness of ethyl linoleate to P. interpunctella larvae was not significantly affected by the silencing of PintOBP18 or PintOBP19 separately. Nevertheless, the attractiveness of this odorant to larvae was severely impaired when both OBPs were knocked down. Furthermore, molecular docking and site-directed mutagenesis studies demonstrated that Ser66 in PintOBP18 and Val62 in PintOBP19 play crucial roles in binding ethyl linoleate. These findings advance our understanding of olfactory recognition in P. interpunctella larvae and provide potential targets for developing olfactory disruption strategies to control storage pests.

Making scents of mosquito repellents

Mosquitoes transmit deadly diseases. Chemical repellents deter mosquitoes from approaching or biting a human host and are an effective behavior-based method of personal protection. However, the current standards for selecting repellents often disregard their mode of action. This has likely led many potential repellents to be overlooked. Here, we discuss the sensory systems that underlie host-seeking behavior and how such behaviors are interrupted by repellents. We explore the behavioral assays used to identify repellents and how these have led a handful of contact repellents (DEET, picaridin, IR3535) to dominate the field. Finally, we consider how the development of spatial repellents may further protect against mosquito-borne diseases.

Diel modulation of perireceptor activity influences olfactory sensitivity in diurnal and nocturnal mosquitoes

Olfaction and diel-circadian rhythm regulate different behaviors, including host-seeking, feeding, and locomotion, in mosquitoes that are important for their capacity to transmit disease. Diel-rhythmic changes of the odorant-binding proteins (OBPs) in olfactory organs are primarily accountable for olfactory rhythmicity. To better understand the molecular rhythm regulating nocturnal and diurnal behaviors in mosquitoes, we performed a comparative RNA-sequencing study of the peripheral olfactory and brain tissues of female Anopheles culicifacies and Aedes aegypti. Data analysis revealed a significant upregulation of genes encoding: OBPs and xenobiotic-metabolizing enzymes including Cytochrome P450 (CYP450) during photophase in Aedes aegypti and the dusk-transition phase in Anopheles culicifacies, hypothesizing their possible function in the regulation of perireceptor events and olfactory sensitivity. RNA interference studies and application of CYP450 inhibitors, coupled with electroantennographic recordings with Anopheles gambiae and Aedes aegypti, established that CYP450 plays a role in odorant detection and antennal sensitivity. Furthermore, brain tissue transcriptome and RNAi-mediated knockdown revealed that daily temporal modulation of neuronal serine proteases may have a crucial function in olfactory signal transmission, thereby affecting olfactory sensitivity. These findings provide a rationale to further explore the species-specific rhythmic expression pattern of the neuro-olfactory encoded molecular factors, which could pave the way to develop and implement successful mosquito control methods.

Knockdown of a chemosensory protein disrupts soil-guided behavior of a subterranean larval pest

In recent years, RNA interference (RNAi) has become a widely studied tool for the functional analysis of genes and more recently, for pest control. Hylamorpha elegans (Coleoptera: Scarabaeidae) is a beetle endemic to Chile, considered an important pest during its larval stage as white grubs, feeding on organic matter (OM) and crop roots (e.g., wheat and red clover). Its control is limited due to its subterranean behavior. Thus, studying a chemosensory system as a fundamental part of the transport and recognition of chemicals from the environment could provide new targets for the knowledge and control of this beetle. Recently, chemosensory genes have been identified for H. elegans white grubs, and a chemosensory protein (CSP) was selected. This study aimed to evaluate the functional role of a highly expressed CSP in the subterranean behavior of white grubs. For this purpose, food preference assays were performed and standardized. Afterward, double-stranded RNA (dsRNA) was synthesized based on a selected CSP. A chosen preference assay was conducted using white grubs treated with dsRNA. Findings showed that white grubs prefer peat with high OM over red clover roots. Additionally, the CSP gene is upregulated when OM content increases. Finally, the knockdown of the CSP led to a disruption in soil-guided behavior. This protein may represent a novel target to be studied in the frame of management strategies for H. elegans.

Odor-Binding Protein 2 in Apis mellifera ligustica Plays Important Roles in the Response to Floral Volatiles Stimuli from Melon and Tomato Flowers

Honeybee olfaction can influence foraging behavior and affect crop pollination. Odor-binding proteins play a vital role in honeybee olfactory perception. A previous study based on the antennal transcriptome of Apis mellifera ligustica in melon and tomato greenhouses revealed that AmelOBP2 is highly expressed. Therefore, we aimed to further investigate the olfactory recognition mechanism of honeybees by detecting the expression levels and binding ability of AmelOBP2 to floral volatiles of melon and tomato flowers. The results show that AmelOBP2 mRNA was highly expressed in the antennae of honeybees, and its protein expression was highest in the antennae at 20 days of age and was higher in the melon greenhouse. The binding ability of AmelOBP2 to floral volatiles of melon was stronger than that of tomato. AmelOBP2 had a stronger binding ability with aldehydes in melon floral volatiles and with terpenes and benzenes in tomato floral volatiles. After feeding with siRNA, the electroantennogram response of honeybees to E-2-hexenal, E-2-octenal, and 1-nonanal decreased markedly, confirming the role of AmelOBP2 in the recognition of melon and tomato floral volatiles. These results elucidate the molecular mechanisms underlying honeybee flower-visiting behavior and provide a theoretical reference for regulating the behavior of honeybees using plant volatiles.

Involvement of sensory neuron membrane protein gene (SNMP) in host plant searching in the bird cherry-oat aphid

Sensory neuron membrane protein (SNMP) gene play a crucial role in insect chemosensory systems. However, the role of SNMP in the host searching behaviour of Rhopalosiphum padi (Hemiptera: Aphididae), a highly destructive pest of cereal crops, has not been clearly understood. Our previous research has shown that three wheat volatile organic compounds (VOCs) - (E)-2-hexenol, linalool, and octanal can attract R. padi, but the involvement of SNMP in the aphid's olfactory response to these wheat VOCs has not to be elucidated. In this study, only one SNMP gene was cloned and characterised from R. padi. The results revealed that the SNMP belongs to the SNMP1 subfamily and was named RpadSNMP1. RpadSNMP11 was predominantly expressed in the antennae of the aphid, with significantly higher expression levels observed in winged forms, indicating that it is involved in olfactory responses of R. padi. RpadSNMP1 expression was significantly up-regulated following starvation, and the expression of this gene showed a decreasing trend after 24 h of aphid feeding. Functional analysis through RpadSNMP1 knockdown demonstrated a significant decrease in R. padi's ability to search for host plants. The residence time of R. padi injected with dsRpadSNMP1 significantly shortened in response to (E)-2-hexenol, linalool and octanal according to the four-arm olfactometer, indicating the crucial role of RpadSNMP1 in mediating the aphid's response to these wheat VOCs. Molecular docking suggested potential binding interactions between RpadSNMP1 and three wheat VOCs. Overall, these findings provided evidence for the involvement of RpadSNMP1 in host plant searching and lay a foundation for developing new methods to control this destructive pest.

Binding Properties of Chemosensory Protein 1 to Plant Volatiles Guiding Nicotiana rustica Recognition in Helicoverpa armigera

Helicoverpa armigera is one of the most serious pests attacking tobacco around the world. Nicotiana rustica is widely used as a trap crop in the fields of Nicotiana tabacum in China. However, the chemical and molecular bases guiding N. rustica recognition in H. armigera are still unknown. In this study, we found 15 volatiles emitted from N. rustica induced EAG responses of H. armigera, while β-ocimene, α-pinene, and linalool were attractive to the moths in Y-tubes. Oviposition tests showed that H. armigera prefers to lay eggs on tobacco plants treated with β-ocimene and α-pinene. Further assays showed that an antenna-enriched chemosensory protein, HarmCSP1, binds robustly with β-ocimene, benzaldehyde, and (Z)-3-hexenyl acetate. Structural analyses revealed that several key amino acid residues are involved in ligand binding. This study increases the understanding of the chemosensory mechanism of H. armigera's recognition of N. rustica and provides the foundation for the design of attractants for H. armigera management.

Identification, distribution and ultramorphology of the larvae of Gynaephora menyuanensis (Lepidoptera: Lymantriinae) endemic to Qinghai-Tibet plateau

The grassland caterpillar is a significant pest of alpine meadows on the Qinghai-Tibet Plateau. Its larvae primarily feed on forage grasses, resulting in financial losses. However, limited research has been done on the morphological features of larvae of this species thus far. The distribution and habitat of Gynaephora menyuanensis were extensively investigated in this instance through field study. The findings indicate that this species is primarily found in the northeast of Qinghai and parts of Gansu Province in alpine meadows at an altitude of 3,000 m. For the first time, SEM is used to report the external morphology and ultramorphology of the first and last instar larvae of G. menyuanensis, including the larval head capsule, mouthparts, antennae, sensilla, thoracic legs, prolegs, and setae. The results indicated that the larvae share similar morphological characteristics except for the number of cutting incisors and crochets. The mature instar larvae have two distinct color funnel warts (yellow and red) on abdominal segments VI and VII, distinguishing them from other lepidopteran larvae. Additionally, the chaetotaxy of the first instar larvae of G. menyuanensis was studied and described in detail, identifying seven clusters (PD, D, SD, L, SV, V, CV) on the larval trunk. This study provides a theoretical basis for the rapid identification of such pests and is beneficial for their monitoring and management.

A deep insight into the sialome of the house fly, Musca domestica, infected with the salivary gland hypertrophy virus (MdSGHV)

The house fly, Musca domestica, serves as a mechanical vector for numerous pathogens, posing a significant risk to human and animal health. More than two decades ago, the Musca domestica salivary gland hypertrophy virus (MdSGHV) was discovered, infecting both males and females flies and disrupting mating and the reproductive process. While MdSGHV can infect various tissues, its primary replication site is the house fly salivary gland. It is well established that arthropod salivary glands play an important role not only in acquiring food but also in transmitting pathogens. Therefore, understanding the composition of vector salivary glands and the interactions between vector and pathogen components is essential for developing future control strategies. To this end, we conducted a comprehensive RNA-sequencing of salivary glands from both infected and non-infected house flies. Our analysis identified a total of 6,410 putative sequences, with 6,309 originating from M. domestica and 101 from the MdSGHV, categorized into 25 functional groups. Furthermore, differential expression analysis between infected and non-infected salivary glands revealed 2,852 significantly modulated transcripts, highlighting profound transcriptional changes triggered by MdSGHV infection. Overall, these findings not only deepen our understanding of the composition of M. domestica salivary glands but also provide valuable insight into the virus-vector interaction, which could serve as a model to understand other medically relevant interactions.

Novel neonicotinoid insecticide cycloxaprid exhibits sublethal toxicity to honeybee (Apis mellifera L.) workers by disturbing olfactory sensitivity and energy metabolism

The risk of neonicotinoid insecticides to honeybees is a global issue. Cycloxaprid (CYC) is a novel neonicotinoid insecticide with outstanding activities, good safety profiles, and no cross-resistance with other neonicotinoids. Information on the environmental risks of CYC is limited, especially its effects on honeybees. Herein, the acute and chronic toxicities of CYC on honeybees were evaluated, and the underlying mechanisms were explored via transcriptomics and molecular docking. The results indicate that CYC had high toxicity to honeybees, with a 48-h oral median lethal dose of 32.8 ng/bee. Over a 10-days of chronic exposure to CYC at sublethal concentration 30 μg/L, the honeybees showed significantly decreased survival rates and food consumption. Additionally, the sensitivity of honeybees to sucrose and odors and CO2 production was significantly reduced. Furthermore, molecular docking revealed that CYC has higher binding affinity than odors to odorant-binding proteins, and the olfactory and metabolism pathways gene expression was negatively affected at transcriptome level. These findings indicate that CYC at sublethal concentration can pose risks to honeybees by affecting their olfactory function and energy metabolic balance. Further study and consideration are needed to fully exploit the benefits of this pesticide.

Conserved and Antenna-Biased Odorant Receptor in the Rape Stem Weevil Ceutorhynchus asper Tuned to Green Leaf Volatiles from Hosts

The rape stem weevil, Ceutorhynchus asper Roel. (Coleoptera: Curculionidae), is a severe pest of oilseed rape. Currently, little is known about the chemosensory functions of odorant receptors (ORs) in coleopterans such as C. asper. Here, the antennal and body transcriptomes of adult C. asper were sequenced and annotated. In total, 49 ORs were identified in C. asper, and transcriptome and quantitative polymerase chain reaction (qPCR) analyses showed that CaspOR5 was antenna-biased. Phylogenetic analyses suggested that homologs of CaspOR5 were conserved among coleopterans. In single sensillum recordings of transgenic flies, CaspOR5 was found to be narrowly tuned to six green leaf volatiles (GLVs) of oilseed rape. Molecular docking indicated that active sites of CaspOR5 bound to GLVs were highly conserved. (E)-2-hexenol, 1-hexanol, and (Z)-3-hexenol were attractive for both sexes of C. asper, and (E)-2-hexenal was only attractive to male weevils. In conclusion, CaspOR5 can facilitate perception of GLVs, thereby playing crucial roles in host plant search and location of C. asper. Our investigation provides insights into the olfactory functions of the conserved CaspOR5 in Coleoptera and can facilitate future research on developing novel green strategies in management of related pest weevils.

Insight into the Relationships Between Chemical, Protein and Functional Variables in the PBP/GOBP Family in Moths Based on Machine Learning

During their lives, insects must cope with a plethora of chemicals, of which a few will have an impact at the behavioral level. To detect these chemicals, insects use several protein families located in their main olfactory organs, the antennae. Inside the antennae, odorant-binding proteins (OBPs), as the most studied protein family, bind volatile chemicals to transport them. Pheromone-binding proteins (PBPs) and general-odorant-binding proteins (GOPBs) are two subclasses of OBPs and have evolved in moths with a putative olfactory role. Predictions for OBP-chemical interactions have remained limited, and functional data collected over the years unused. In this study, chemical, protein and functional data were curated, and related datasets were created with descriptors. Regression algorithms were implemented and their performance evaluated. Our results indicate that XGBoostRegressor exhibits the best performance (R2 of 0.76, RMSE of 0.28 and MAE of 0.20), followed by GradientBoostingRegressor and LightGBMRegressor. To the best of our knowledge, this is the first study showing a correlation among chemical, protein and functional data, particularly in the context of the PBP/GOBP family of proteins in moths.

Synergistic effect of β-ocimene on Hyphantria cunea sex pheromone and its potential attraction mechanism related to Ca2+ stimulation

Hyphantria cunea, a globally significant quarantine pest, causes severe ecological and economic impacts in invaded regions. Attractants are environment-friendly and valuable pest management tools for H. cunea control. In this study, we identified that the combination of β-ocimene with sex pheromone components was strongly attractive to H. cunea males. This attractant combination activates the Ras signaling pathway and stimulates Ca2+ in male adults following exposure. Feeding and oviposition behavior results demonstrated that H. cunea prefers Morus alba over Platanus × acerifolia, Metasequoia glyptostroboides, and Taxodium distichum. In the fresh branches of M. alba with leaves, the relative abundance of β-ocimene (36.33 ± 0.41 %) was significantly higher than the other hosts. Electroantennography recordings, behavioral choice assays, and field trapping trials showed that the combination of β-ocimene with sex pheromone components significantly enhanced male response and attraction. The number of trapped males using β-ocimene/ sex pheromone blend was 3.7-fold higher than that of sex pheromone or β-ocimene alone in the field, indicating a synergistic effect of adding β-ocimene to sex pheromone. The molecular mechanism of β-ocimene/sex pheromone synergism was further analyzed. After exposure to the attractant, the Ras signaling pathway in the heads of males are activated (HcILP and HcPLCε1 are upregulated, while HcRasGAP and HcPLD are downregulated), which further stimulates the expression of IP3 and Ca2+. The activation of Ca2+ may be the key reason for its higher attraction to males. These findings provide a theoretical basis for the selection and mechanistic understanding of attractants for H. cunea, offering insights for attractant-based pest control strategies.

Adaptive evolution of traits for parasitism and pathogen transmission potential in bat flies

Deciphering the mechanisms underlying the transmission and spillover of zoonoses from reservoir hosts is essential in preventing future global pandemics. Bat flies-obligate blood-feeding ectoparasites of bats-are known carriers of diverse viruses. Here, we conducted a de novo assembly of a chromosome-level genome for the bat fly species Phthiridium sp. Comparative genomic analysis unveiled genes associated with specialized traits, such as the loss of eyes and wings, as well as elongated legs, which have adapted to parasitism on the dense fur of bats. Utilizing small RNA sequencing, we identified a spectrum of known and previously unclassified viruses in bat flies. Notably, experimental evidence indicated that bat flies can also feed on mammalian hosts other than bats, suggesting the potential for the spillover of bat-borne viruses. Furthermore, we demonstrated the role of the bat fly's RNA interference pathway in influencing the diversity and evolution of viruses. In summary, this study not only presents a new genome catalog to unveil the evolutionary mechanisms underpinning bat fly parasitism, but also provides a novel research system that can be used to investigate the mechanisms of cross-species transmission of bat-borne viruses and the co-evolution of bats and viruses.

A dual sensing mechanism of eastern honeybee Apis cerana that upregulates the expression level of chemosensory protein CSP1 and enhances the binding affinity to loquat floral volatiles at low temperature

As a native bee species, the eastern honeybee (Apis cerana) plays an essential role in pollinating loquat flowers, which bloom in early winter in China. This pollination behavior is closely related to A. cerana's ability to adapt to low temperatures, which depends on the functionality of its chemoreceptive system. Transcriptome analysis revealed a significant upregulation of the A. cerana chemosensory protein 1 (CSP1) gene at low temperatures. Fluorescence competitive binding experiments indicated that nine chemical volatiles from loquat flowers exhibited a stronger binding affinity to CSP1 than to odorant binding protein 2 (OBP2). Thermodynamic analysis revealed that CSP1's binding affinity increases at low temperatures, with a static binding mechanism largely influenced by the specific volatile molecule rather than the type of olfactory soluble protein. Molecular docking and site-directed mutagenesis confirmed that F44 residue may play a key role in CSP1's binding to three primary volatile compounds. In summary, the present study identified a dual sensing mechanism in which low temperatures upregulated the expression of CSP1 and enhanced the binding affinity of CSP1 to loquat flower volatiles. These findings not only clarify A. cerana's chemoreceptive mechanism toward loquat flower volatiles in pollination but also provide a theoretical basis for further exploring ecological adaptations between native bees and early-winter flowering plants.

An antennal-specific OBP mediates bait odorant perception in fire ants

Odorant binding proteins (OBPs) play a key role in the crosstalk between the external environment and dendritic neuron activation. Ham sausage is an efficient bait widely used for monitoring the invasive ant Solenopsis invicta in the field, whereas the chemoreceptors involved in bait odorant perception in S. invicta have not been functionally characterized. Here, we investigated the role of SiOBP2, an OBP specifically expressed in the antenna, from S. invicta in detecting bait odorants. SiOBP2 was specifically expressed in sensillum basiconca in S. invicta antennae and displayed strong binding affinity and diverse binding mechanisms with specific bait odorants, such as static quenching and multiple binding characteristics with 3-mercapto-2-butanone and furfuryl mercaptan. Knockdown of SiOBP2 abolished the electroantennogram and behavioral responses of S. invicta to these odorants. S. invicta with SiOBP2 knockdown exhibited inactivation of odorant receptor neuron signaling and reduced bait searching efficiency. Foraging behavior and sensory cone responses to bait odorant stimuli in S. invicta demonstrate the sensillum basiconca is particularly tuned to 3-mercapto-2-butanone and furfuryl mercaptan. Collectively, SiOBP2 is essential for the perception of S. invicta on bait odorants and can be used as an important molecular target to develop novel attractants for S. invicta.

Molecular evolution of dietary shifts in ladybird beetles (Coleoptera: Coccinellidae): from fungivory to carnivory and herbivory

BACKGROUND

Dietary shifts are major evolutionary steps that shape ecological niches and biodiversity. The beetle family Coccinellidae, commonly known as ladybirds, first transitioned from a fungivorous to an insectivorous and subsequently a plant diet. However, the molecular basis of this dietary diversification remained unexplored.

RESULTS

We investigated the molecular evolution of dietary shifts in ladybirds, focusing on the transitions from fungivory to carnivory (Coccinellidae) and from carnivory to herbivory (Epilachnini), by comparing 25 genomes and 62 transcriptomes of beetles. Our analysis shows that chemosensory gene families have undergone significant expansions at both nodes of diet change and were differentially expressed in feeding experiments, suggesting that they may be related to foraging. We found expansions of digestive and detoxifying gene families and losses of chitin-related digestive genes in the herbivorous ladybirds, and absence of most plant cell wall-degrading enzymes in the ladybirds dating from the transition to carnivory, likely indicating the effect of different digestion requirements on the gene repertoire. Immunity effector genes tend to emerge or have specific amino acid sequence compositions in carnivorous ladybirds and are downregulated under suboptimal dietary treatments, suggesting a potential function of these genes related to microbial symbionts in the sternorrhynchan prey.

CONCLUSIONS

Our study provides a comprehensive comparative genomic analysis to address evolution of chemosensory, digestive, detoxifying, and immune genes associated with dietary shifts in ladybirds. Ladybirds can be considered a ubiquitous example of dietary shifts in insects, and thus a promising model system for evolutionary and applied biology.

Binding Properties of the General Odorant-Binding Protein GOBP2 to Herbicides and Insecticides in Spodoptera litura

We previously reported that the general odorant-binding protein GOBP2 enhances chlorpyrifos tolerance in Spodoptera litura by perceiving the herbicides. However, the direct interaction between GOBP2 and pesticides remains unknown. Herein, we verified the effect of the direct binding of GOBP2 to pesticides on the herbicide-induced insecticide tolerance in S. litura. Fluorescence competitive binding assays indicated that GOBP2 exhibits high binding affinities to the herbicide trifluralin and the insecticides indoxacarb, chlorpyrifos, and fipronil, with Ki values ranging from 1.95 to 13.01 μM. Moreover, Ala136 and Thr30 were determined as the key binding sites of GOBP2 to the pesticides through molecular docking and site-directed mutagenesis. Finally, the knockdown of GOBP2 significantly increased the larval susceptibility to trifluralin and three types of insecticides. Our findings provide a valuable reference for the further exploration of the molecular mechanisms underlying herbicide-induced insecticide tolerance in S. litura, laying the foundation for innovative pest management strategies.

Chemosensory Proteins Protect Nilaparvata lugens from Imidacloprid by Sequestering the Insecticide and Facilitating Metabolic Detoxification

The involvement of chemosensory proteins (CSPs) in binding to insecticides has been implicated. However, our understanding of CSP-mediated insecticide resistance remains limited. Herein, 15 CSP genes were identified and characterized from Nilaparvata lugens. Expression analysis identified six CSPs with overexpression in the imidacloprid-resistant strain, whose involvement in imidacloprid resistance was validated by RNA interference. Among them, four CSPs were successfully expressed using a prokaryotic expression system, and their binding affinities to imidacloprid were confirmed through fluorescence competitive binding assays. Knockdown of them impaired the capacity of N. lugens to metabolize imidacloprid and inhibited the activity of metabolic detoxification pathways, while their overexpression in Escherichia coli enhanced bacterial metabolic efficiency toward imidacloprid. Furthermore, the transcriptional regulation of CSP2 and CSP15 was found to be mediated by AhR/ARNT and CncC/MafK. These findings suggest that the overexpression of CSPs in N. lugens promotes imidacloprid resistance by sequestering the insecticide and enhancing metabolic detoxification.

Genome-Wide Identification and Expression Profiling of Odorant-Binding Protein Genes in the Bean Flower Thrips Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae)

Megalurothrips usitatus is an economically important vegetable pest. Because of the growing demand for reducing pesticide use on vegetables, new environmentally friendly strategies for controlling M. usitatus are urgently needed. Insect odorant-binding proteins are prospective targets for screening environmentally friendly odorant attractants for pest control. However, very little is known about OBP genes in M. usitatus. Here, we identified 14 OBPs in the M. usitatus genome using HMMER and BLAST. The chromosomal location showed that these OBPs were widely distributed across eight chromosomes. The analysis of the gene and protein structure characteristics of OBPs in M. usitatus revealed substantial diversity within the OBP gene family. The spatiotemporal expression profiles showed that ten out of 14 MusiOBPs displayed male biased expression, which were highly expressed in antennae, suggesting that they may play a crucial role in the recognition of host plant volatiles and thrips aggregation pheromones. Notably, only MusiOBP8 was significantly higher expressed in female adults, indicating a potential involvement in reproduction. Moreover, MusiOBP7 and MusiOBP13 were highly expressed in the pupae, indicating their possible role in immune responses. These results provide an important foundation for further exploration of the functions of the OBPs in M. usitatus.

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.

Transcriptome Profiling of Euproctis pseudoconspersa Reveals Candidate Olfactory Genes for Type III Sex Pheromone Detection

The tea tussock moth (Euproctis pseudoconspersa) is a common tea plantation pest with Type III sex pheromone components (SPCs). However, the olfactory genes involved in the perception of Type III SPCs remain unknown. To identify the olfactory genes involved in E. pseudoconspersa olfactory perception, we sequenced the transcriptomes of different tissues from male and female moths. We identified 27 chemosensory proteins, 39 odorant-binding proteins (OBPs), 28 ionotropic receptors (IRs), and 67 odorant receptors (ORs). Phylogenetic and antennal abundance analyses showed that EpseOR12, EpseOR13, EpseOR15, EpseOR16, and EpseOR18 belonged to the pheromone receptor clades of Type II moths, with predominant expression in male antennae. Besides these EpseORs, EpseOR14 and EpseOR32 were two of the most abundant EpseORs in male antennae, where they were predominantly expressed. Four pheromone-binding proteins (PBPs) were identified, with higher expression in male antennae. EpseORs and EpsePBPs may be involved in Type III SPC detection. Additionally, a few EpseOBPs, EpseIRs, and EpseORs were predominantly expressed in either male or female antennae. These genes may play important roles in olfaction and may be involved in detecting host plant volatiles and pheromones. These results provide a foundation for further exploration of the molecular mechanisms of E. pseudoconspersa olfaction.

Where do all the pests go? Understanding the genomic mechanisms of crop pest dynamics during the off-season

Agroecosystems provide abundant resources to insects. However, throughout the off-season, insects must overcome resource shortages and adverse climates to survive. This off-season persistence affects pest infestations in subsequent crops or seasons. Key pest species employ diapause, migration, and local-scale dispersal to persist during the off-season. Genomic approaches have advanced our understanding of these survival mechanisms. Clock genes regulate the circadian rhythm and interact with neuropeptides and downstream pathways, such as insulin-like peptides and hormonal factors-like ecdysteroids and juvenile hormones that regulate diapause. Migrant insects must manage processes like energy metabolism, oogenesis, and flight orientation. Local-scale dispersal requires mechanisms to locate, select, and exploit the most suitable host and habitat for survival and reproduction during the off-season. Here, we present advances in genomic research on pest survival during the off-season, focusing on diapause, migration, and local-scale dispersion. Understanding these phenomena is crucial for developing and optimizing effective integrated pest management programs.

Identification of Candidate Olfactory Genes in the Antennal Transcriptome of Loxostege sticticalis Trapped by Three Different Sex Pheromone Blends

Insects sense intraspecific or interspecific information about the chemical substances in the habitat through the sensitive olfactory system to carry out foraging, mating, oviposition, and other activities. The antennae serve as the primary olfactory organs in insects. The olfactory process involves the participation of many proteins, such as odorant-binding proteins (OBPs) and odorant receptors (ORs), but ORs play a central role in olfactory specificity and sensitivity. The beet webworm, Loxostege sticticalis, is an omnivorous agricultural pest that endangers crops and poses a significant risk to the agricultural and animal husbandry production in northern China. In this study, Illumina sequencing was conducted on the antennal transcriptome of male L. sticticalis trapped by three different sex pheromone blends. A total of 10,320 DEGs were identified, from which 46 candidate olfactory genes were selected for further analysis. These candidate olfactory genes comprise 13 odorant receptors, 6 ionotropic receptors (IRs), 3 gustatory receptors (GRs), 12 odorant-binding proteins, and 13 chemosensory proteins (CSPs). In summary, we analyzed the antennal transcriptome of male L. sticticalis trapped by three different sex pheromone blends and identified several candidate olfactory genes. This discovery offers a foundation for further molecular-level investigations into the olfactory system of L. sticticalis.

An odorant-binding protein functions in fire ant social immunity interfacing with innate immunity

Social immunity-mediated sanitation behaviours occur in insects when microbially killed corpses are removed and/or dismembered by healthy nestmates. However, little is known concerning the chemical signals or receptor proteins that mediate these responses. Here, we identify cuticular components in the eusocial red important fire ant, Solenopsis invicta: behenic acid, which induces dismemberment behaviour, and oleic and cis,cis-9,12-linoleic acids, which inhibit dismemberment in a process mediated by S. invicta odorant-binding protein-15 (SiOBP15). Yeast two-hybrid screening and protein-protein interaction analyses identified the ant immunity-related proteins apolipophorin-III (SiApoLp-III) and fatty acid binding protein-5 (SiFABP5) as SiOBP15 interacting partners. SiOBP15 and SiFABP5 bound all three dismemberment-related compounds, whereas interactions between SiOBP15 and SiApoLp-III narrowed binding to behenic acid. RNAi-mediated gene expression knockdown of SiOBP15, SiApoLp-III or SiFABP5 revealed that behenic acid chemoreception determines dismemberment behaviour via SiApoLp-III/SiOBP15, whereas SiOBP15 or SiOBP15/SiFABP5 recognition of linoleic acid inhibits dismemberment behaviour. These data identify a host circuit linking olfactory proteins and proteins involved in innate immunity to control the degree of sanitation behaviour elicited in response to microbial infection. We identify specific chemical cues transduced by these proteins, providing a mechanism connecting olfaction-related processes to innate immunity, host-pathogen interactions and social immunity.

Molecular characterisation and expression profiles of an odorant-binding proteins gene (FoccOBP9) from Frankliniella occidentalis

Insect odorant-binding proteins (OBPs) are the key proteins in insect olfactory perception and play an important role in the perception and discrimination of insects. Frankliniella occidentalis is a polyphagous pest and seriously harms the quality and yield of fruits, flowers and crops worldwide. Therefore, the discovery of OBPs has greatly improved the understanding of behavioural response that mediates the chemoreception of F. occidentalis. To identify the OBP gene of F. occidentalis and its sequence and expression, rapid amplification cDNA ends (RACE) and qRT-PCR reaction system were performed. The results showed that the sequence of FoccOBP9 gene was 846 bp and the reading frame was 558 bp, encoding 185 amino acid residues, a 3' non-coding region of 195 bp and a 5' non-coding region of 93 bp.The molecular weight of the protein was about 20.08 kDa, and the isoelectric point was 8.89. FoccOBP9 was similar to AtumGOBP and CnipOBP2 (30%), followed by BdorGOBP, DficGOBP, DsuzGOBP, AalbOBP38, CmarOBP6 and SexiOBP. Phylogenetic analysis of the FoccOBP9 demonstrated that the FoccOBP9 had a relatively close evolutionary relationship with SgreOBP1, AtumGOBP, HeleOBP3, CbowOBP17, CnipOBP2 and CpalOBP2. The prediction of secondary structure showed that FoccOBP9 protein contained 135 amino acid residues forming α-helix, 91 amino acid residues forming β-sheets and 24 amino acid residues forming β-turning. However, three-dimensional structure prediction showed that the FoccOBP9 protein skeleton was composed of six α-helices and the loops connecting these helices. Dynamic observation of the three-dimensional structure revealed that five α-helices (α1, α2, α4, α5, α6) were found in the structure. The expression profiles analysis revealed that FoccOBP9 are highly abundant in antenna significantly, followed by the head and belly, and almost no expression in the chest and foot. Therefore, the identification and analysis of OBP may be useful for monitoring and limiting the damage of F. occidentalis.

Female contact sex pheromone recognition in the German cockroach (Blattella germanica) is mediated by two male antennae-enriched sensory neuron membrane proteins

BACKGROUND

The German cockroach Blattella germanica is a notorious urban health pest that has developed resistance to multiple pesticides. Thus, novel non-lethal pest control agents are urgently needed. Olfaction interference via disruption of sex pheromone recognition-related genes offers a promising approach. The German cockroach has a unique courtship behavior in which female adults emit contact sex pheromones (CSPs) in response to antennal touching, which subsequently triggers distinctive male sex behavioral responses. Due to the limited volatility of CSPs, the molecular mechanisms underlying their recognition and the specific olfactory pathways activated remain poorly defined. Although the odorant receptor coreceptor (Orco) is critical for most insect olfaction, sensory neuron membrane proteins (SNMPs), in particular SNMP1, also play crucial roles in sex pheromone recognition in moths and flies. While multiple SNMP1 homologs have been identified in multiple insect species, they have yet to be fully functionally characterized in cockroaches.

RESULTS

In this study, RNA-interference (RNAi)-mediated knockdown of BgerOrco reduced both the electrophysiology responses and courtship behaviors of males, indicating CSP perception proceeds via an olfaction pathway. Similar RNAi knockdown of BgerSNMP1e and BgerSNMP1d, which are predominantly expressed in male antennae, revealed critical roles in perceiving the major component of the Blattella germanica CSP blend. Unlike BgerSNMP1e, BgerSNMP1d was also found to function in the perception of the minor CSP component. Molecular docking analyses revealed no differences in the binding affinities of BgerSNMP1d for the major and minor CSP components, whereas the binding affinities of BgerSNMP1e displayed clear selectivity for the major component.

CONCLUSION

Our results show that the olfactory pathway is critical for CSP recognition and that two male-enriched SNMP genes, BgerSNMP1e and BgerSNMP1d, are crucial factors mediating the male response to CSP stimulation in German cockroaches. This study lays a foundation for studying the mechanisms of CSP recognition and provides novel molecular targets with potential to be exploited as disruptors of courtship behavior. © 2024 Society of Chemical Industry.

Main Chemical Components, Activity and Mechanism of Repellence of Cyperus esculentus Essential Oil Against Tribolium confusum

Tribolium confusum is a major stored-product pest that exhibits resistance to chemically synthesized pest repellents. This study investigated the potential of essential oil (EO) extracted from the roots of Cyperus esculentus as a natural alternative for pest management. The EO was obtained through steam distillation, and its chemical composition was elucidated using gas chromatography-mass spectrometry. The primary compounds, cyperotundone and cyperene, were further isolated from the EO through silica gel column chromatography. The efficacy of the EO and its isolated compounds as pest repellents was evaluated against a flaxseed pest, which was identified as T. confusum through DNA sequence analysis. The results demonstrated that at 86.12 μg/cm2, the EO and its two main components maintained significant repellent activity for up to 24 h. In contrast, the effectiveness of the positive control, N, N-diethyl-3-methylbenzamide (DEET) declined rapidly after 8 h. At 16 h, the repellent activity of the EO and one of its main components, cyperotundone, was significantly greater than that of DEET. Furthermore, at a lower concentration of 43.06 μg/cm2, cyperotundone's repellent activity was significantly stronger than DEET's at 16 h. Additionally, cyperotundone outperformed DEET significantly from 4 to 16 h at 21.53 μg/cm2 and at 16 h at 10.76 μg/cm2. Among the two compounds, cyperotundone exhibited a longer-lasting repellent effect compared to cyperene, which is consistent with the lower evaporation rate of cyperotundone. Biochemical assays revealed that exposure to the EO of C. esculentus and its major compounds significantly reduced (p < 0.05) the activities of acetylcholinesterase and glutathione-S-transferase in T. confusum. Molecular docking experiments indicated that the compounds could bind to olfactory receptors with low binding energies. qRT-PCR analysis revealed that the EO and its two compounds significantly altered (p < 0.05) the expression levels of odorant receptor genes in the pest. These findings suggest that the repellent action of C. esculentus EO and its major compounds on T. confusum may be mediated through the modulation of the pest's olfactory system, as well as by inhibiting essential enzymatic activities in the pests. This research contributes valuable insights into the development of sustainable, long-lasting, and eco-friendly pest repellents, harnessing the potential of the rich botanical resource C. esculentus.

Structure-Function Analysis of Volatile (Z)-3-Fatty Alcohols in Tomato

Plants emit green leaf volatiles (GLVs) in response to biotic and abiotic stress. Receiver plants perceive GLVs as alarm cues resulting in activation of defensive or protective mechanisms. While this is well documented, it is not known how GLVs are perceived by receiver cells and what the structural determinants are for GLV activity. We tested whether the carbon chain length in (Z)-3-fatty alcohols with four to nine carbons and the double bonds in six-carbon alcohols contribute to bioactivity. In Solanum peruvianum suspension-cultured cells we found that (Z)-3-fatty alcohols, except (Z)-3-butenol, induce medium alkalinization and MAP kinase phosphorylation, two signaling responses often tied to the perception of molecular patterns that function in plant immunity and resistance to herbivores. In tomato (S. lycopersicum) seedlings, we found that (Z)-3-fatty alcohols induce inhibition of root growth. In both signaling and physiological responses, (Z)-3-octenol and (Z)-3-nonenol had a higher bioactivity than (Z)-3-heptenol and (Z)-3-hexenol, with (Z)-3-butenol only being active in root growth assays. Bioactivity correlated not only with chain length but also with lipophilicity of the fatty alcohols. The natural GLVs (E)-2-hexenol and the saturated 1-hexanol exhibited a higher bioactivity in pH assays than (Z)-3-hexenol, indicating that the presence and position of a double bond also contributes to bioactivity. Our results indicate that perceiving mechanisms for (Z)-3-fatty alcohols show a preference for longer chain fatty alcohols or that longer chain fatty alcohols are more accessible to receptors.

Molecular evidence for the role of the ovipositor of the fall armyworm: Where to lay or not to lay?

Oviposition behavior in insects has received considerable attention, but studies have mainly focused on the antennae, neglecting the role of the ovipositor. In this study, we investigated the functional characteristics of the ovipositor in oviposition site selection by the fall armyworm (FAW) Spodoptera frugiperda, a destructive invasive pest of maize and other cereals. In oviposition choice assays females exhibited significant repellency to isothiocyanate (ITC), volatiles specific to non-preferred cruciferous plants. Females retained repellency to ITC or attraction to maize volatiles even after antennae removal. Scanning electron microscopy indicated the presence of olfactory-associated sensilla on the ovipositor. Comparative transcriptome analysis and in vitro functional studies showed that S. frugiperda odorant binding protein 30 (SfruOBP30), exclusively expressed in the ovipositor, displayed a broad sensitivity toward 18 maize volatiles and 10 ITC compounds. Site-directed mutant assay revealed that Ser71 and Ser85 were the key binding sites for SfruOBP30 interacting with ITCs and key maize volatiles, respectively. Silencing the expression of SfruOBP30 resulted in the loss of bias in oviposition of FAW, significantly inhibiting their ability to avoid ITCs and locate the maize substrate. Overall, we propose that the ovipositor does not just seek out advantageous conditions for immature stages but more importantly, avoids potential risks during the oviposition process. Apparently, the involvement of SfruOBP30 plays a critical role in detecting both beneficial and harmful substances during this intricate process.

AmelOBP4: an antenna-specific odor-binding protein gene required for olfactory behavior in the honey bee (Apis mellifera)

BACKGROUND

Odorant binding proteins (OBPs) initiate the process of odorant perception. Numerous investigations have demonstrated that OBPs bind a broad variety of chemicals and are more likely to carry pheromones or odor molecules with high binding affinities. However, few studies have investigated its effects on insect behavior. Previously, we found that AmelOBP4 has a significantly higher expression in the heads of foragers than that of nurses regardless of their ages, revealing its importance in foraging behaviour of the honey bee. RNA interference (RNAi) is the induction of sequence specific gene silencing by double-stranded RNA (dsRNA), it is a powerful tool that makes gene inactivation possible in organisms that were not amenable to genetic analysis before.

RESULTS

In this study, we found that AmelOBP4 had high expression levels in the antennae of both nurses and foragers, and could be successfully inhibited by feeding double stranded RNA of AmelOBP4 (dsAmelOBP4). Foragers with inhibited AmelOBP4 showed significantly lower sugar responsiveness than control bees, and also significantly reduced EAG response to plant volatiles of nonanal, linalool and 1-Octen-3ol. On the other hand, nurses with inhibited AmelOBP4 showed significantly reduced EAG response to brood pheromone of ethyl oleate, methyl linoleate, methyl palmitate and β-ocimene. Finally, the Y-tube choice assay showed nurses only exhibited a significantly reduced preference to ethyl oleate, but foragers exhibited significantly reduced preference to all these three plant volatiles.

CONCLUSIONS

The findings of our study suggested that AmelOBP4 plays an important role in the odorant binding process, especially in modulating olfactory behaviour in workers. Our results provide a foundation for exploring the olfactory mechanism of Apis mellifera.

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.

High Antennal Expression of CYP6K1 and CYP4V2 Participate in the Recognition of Alarm Pheromones by Solenopsis invicta Buren

Insects have highly developed olfactory systems in which cytochrome P450s (CYPs) were involved as odor-degrading enzymes throughout the olfactory recognition of odor compounds by insects to avoid continuous stimulation of signaling molecules and thus damage to the olfactory nervous. To understand whether the highly expressed CYPs in the antennae play an olfactory function in Solenopsis invicta worker, in this study, we find six highly expressed antennal CYPs from the transcriptome of S. invicta. Multiple sequence alignment and phylogenetic analysis divided them into two families: the CYP3 family (SinvCYP6K1, SinvCYP6K1-1) and the CYP4 family (SinvCYP4C1, SinvCYP4C1-1, SinvCYP4C1-2, SinvCYP4V2). The expression patterns of these six CYPs were analyzed by RT-qPCR, which revealed that SinvCYP6K1 and SinvCYP4V2 were only highly expressed in the antennae of adult workers. The expression of SinvCYP6K1 and SinvCYP4V2 in workers was markedly diminished after feeding with dsRNA. The electroantennography (EAG) assay demonstrated that the silencing of either SinvCYP6K1 or SinvCYP4V2 resulted in a notable reduction in the EAG response of workers to 2-ethyl-3,6(5)-dimethylpyrazine (EDMP). Furthermore, the trajectory behavior assay showed that the worker's range and speed of movement in response to EDMP significant decreased after the silencing of SinvCYP6K1 and SinvCYP4V2. The findings indicated that both SinvCYP6K1 and SinvCYP4V2 were implicated in the recognition of EDMP by S. invicta.

Screening, validation and functional characterization of genes encoding proteins that interact with sensory neuron membrane protein 1b (SNMP1b) from Cyrtotrachelus buqueti (Coleoptera: Curculionidae)

Sensory neuron membrane proteins (SNMPs) play critical roles in insect olfactory system. However, functional studies outside of Drosophila remain limited, especially in Coleoptera species. In our previous study, a SNMP1 (CbuqSNMP1b) was identified from Cyrtotrachelus buqueti (Coleoptera: Curculionidae), an insect pest that seriously influence the development of the bamboo industry. Here in a membrane protein yeast two-hybrid system, protein interactions between CbuqSNMP1b as a bait protein and a cDNA library of antenna of male C. buqueti adults as prey protein were assessed. Of 29 proteins identified as putative interactors, the Minus-C odorant-binding protein (CbuqOBP1) was selected for further analysis. The interaction between CbuqSNMP1b and CbuqOBP1 was further confirmed by both the in vivo yeast spotting analysis and the in vitro glutathione-S-transferase pull-down assay. Fluorescence binding assays indicated that the interaction between CbuqSNMP1b and CbuqOBP1 could enhance the binding abilities of CbuqOBP1 to four adult C. buqueti biologically active volatiles. The knockdown of CbuqSNMP1b + CbuqOBP1 expression by RNA interference significantly reduced the behavior responses of male adults to ethyl hexanoate and trans,trans-2,4-Nonadienal. These results increase our understanding of insect SNMP1 and will aid in exploring the underlying mechanisms of CbuqSNMP1b functions in the future.

Mechanistic exploration of odorant binding protein-mediated chlorpyrifos resistance in Nilaparvata lugens: Insights from insecticide sequestration and transcriptional regulation

The effectiveness and sustainable application of insecticides are severely threatened by the rapid evolution of resistance in agricultural pests. Recent research indicates that odorant binding proteins (OBPs) may be involved in facilitating insecticide resistance, while the specific mechanisms remain poorly understood. Herein, 11 OBPs were identified from Nilaparvata lugens. Among them, OBP5 exhibited high and specific expression in the head, and showed constitutive overexpression in the chlorpyrifos-resistant strain. Knockdown of OBP5 notably restored susceptibility to chlorpyrifos in N. lugens, while overexpression of OBP5 in Escherichia coli significantly enhanced bacterial tolerance to chlorpyrifos. Fluorescence competitive binding assay confirmed the strong binding affinities of OBP5 to chlorpyrifos and its active metabolite chlorpyrifos-oxon. Molecular docking studies proposed a critical interacting amino acid (Lys147) in the binding site, which was further validated by comparative binding studies between wildtype OBP5 and the mutated protein OBP5K147A. Furthermore, Lim1β that also presented overexpression pattern in the resistant strain, was found to regulate expression of OBP5 through a dual-luciferase reporter assay. Our findings demonstrate that the overexpression of OBP5 contributes to chlorpyrifos resistance by binding and sequestering the insecticides, shedding light on the sequestration resistance mechanism conferred by OBPs and offering potential targets for resistance management.

Binding properties of olfactory proteins to host volatiles, free fatty acids and cuticular hydrocarbons in the termite Reticulitermes aculabialis

As eusocial insects prevalent in tropical and subtropical regions, termites are characterized by highly organized behaviors and exceptional adaptability, rooted in caste differentiation and chemical communication. These traits make them excellent models for studying insect social structures and ecological interactions. Investigating how termites use chemical signals to perceive and respond to their environment provides insights into their coordination and adaptation within complex ecosystems. This study delved into the chemosensory mechanisms of Reticulitermes aculabialis, examining the interactions of four olfactory proteins with 70 ligands, including host volatiles, cuticular hydrocarbons (CHCs), and free fatty acids (FFAs). Molecular docking simulations revealed varied affinities of the olfactory proteins for long-chain hydrocarbons (n-C23 to n-C28), suggesting a nuanced chemical communication system through specific hydrocarbon detection. RacuCSP1 and RacuCSP2 exhibited specific binding to linoleic acid and undecanoic acid, respectively, highlighting the significance of FFAs in the physiological and behavioral processes of termites. The four olfactory proteins showed a strong affinity for longifolene in fluorescence competitive binding experiments. Notably, RacuOBPs exhibited unique affinities for terpenoid volatiles such as β-lonone and neocembrene, while RacuCSPs specifically bound with terpenoids like 3-carene, myrtenol, α-pinene oxide and β-pinene indicating their critical roles in host detection. Behavioral observations following gene silencing revealed that RacuOBP5 was essential for recognizing longifolene and α-lonone recognition, while RacuCSP1 was key for detecting α-pinene in termites. These findings enhance our understanding of the termite chemosensory system and offer insights for developing precise pest management strategies.

Key amino acids in odorant-binding protein OBP7 enable Bradysia odoriphaga to recognize host plant volatiles

Bradysia odoriphaga (Diptera: Sciaridae) is a devastating underground pest that can cause serious economic losses. Odorant binding proteins (OBPs) are crucial components of the insect olfactory system, playing key roles in locating host plants, oviposition sites, and mates. Therefore, they are considered potential targets for pest control. Here, we obtained one OBP gene (BodoOBP7) from the antennal transcriptome of B. odoriphaga, and observed that the expression level of BodoOBP7 was primarily in the antennae of both sexes, with significantly higher expression level in females than in males. Fluorescence competitive binding assays indicated that BodoOBP7 exhibited strong binding affinities for the six host plant volatiles, including propyl disulfide, dipropyl trisulfide, dimethyl trisulfide, 2-tridecanone, 2-undecanone and alpha-ionone. Subsequently, homology modeling, molecular docking and site-directed mutagenesis revealed that four key amino acid residues (Phe79, Phe99, Ile96, Leu100) participate in the binding of BodoOBP7 with six host plant volatiles. Our results demonstrate that BodoOBP7 is involved in olfactory recognition in B. odoriphaga. These findings may enhance our understanding of the interaction mechanisms between host plants and B. odoriphaga, potentially offering new perspectives for the development of effective green control strategies.

The olfactory recognition between leaf-cutter bee Megachile saussurei and alfalfa floral volatiles mediated by odorant binding protein 4 (MsauOBP4)

Megachile saussurei (Hymenoptera, Megachilidae) is a primary insect pollinator of alfalfa (Medicago sativa L.) in northwestern China. However, the mechanisms underlying the olfactory responses of M. saussurei induced by alfalfa volatiles is still unclear. Here, the interaction between MsauOBP4 and alfalfa floral volatiles was first elucidated. Results suggested that thirty-two alfalfa floral volatiles were identified and MsauOBP4 was successfully expressed with the consistent molecular mass as predicted results. MsauOBP4 displayed a broad binding spectrum to 32 volatiles, among which MsauOBP4 showed the strongest binding ability to (Z)-3-Hexen-1-ol. In the Y-tube olfactometer behavioral bioassay, M. saussurei elicited the most significant behavioral preference (Z)-3-Hexen-1-ol. MsauOBP4 showed an optimal binding feature to (Z)-3-Hexen-1-ol and valine was the key residue in binding the ligands. After silencing the MsauOBP4, the preference and EAG values of M. saussurei to (Z)-3-Hexen-1-ol were significantly decreased and selection rate of M. saussurei to alfalfa flowers dropped to 57.50 % from 83.33 %. These findings indicated that (Z)-3-Hexen-1-ol is a crucial component in the host location process mediated by MsauOBP4.

Phenotypic Plasticity in Locusts: Trade-Off Between Migration and Reproduction

Locusts exhibit phenotypic plasticity in response to population density changes, with distinct phenotypes in the solitary and gregarious phases. In the past decade, many studies have revealed the molecular mechanisms underlying phase changes, which include the change of body coloration, pheromones, behavior, flight, fecundity, immunity, and aging. Our understanding of the molecular mechanisms related to these phenotypic differences has expanded in breadth and depth with the decoding of the locust genome, involving transcriptional, post-transcriptional, translational, and epigenetic regulation. Large-scale regulation networks composed of genes and noncoding RNAs reflect the systematic modifications of the locust phase transition in response to environmental changes. Gene manipulation techniques have verified the functions of specific genes and related pathways in phase changes. This review highlights the latest advances in studies of locust phase changes and suggests that the divergence of energy and metabolism allocation in gregarious and solitary locusts is an adaptive strategy for long-distance migration and local reproduction, respectively. Finally, we propose future research directions and discuss emerging questions in the area of phenotypic plasticity of locusts.

Plant Volatile Methyl Salicylate Primes Wheat Defense Against the Grain Aphid by Altering the Synthesis of Defense Metabolites

Wheat (Triticum aestivum L.) is one of the most important staple crops all over the world. Its productivity is adversely affected by aphid infestation. Plant volatiles play a critical role in plant communication, inducing direct and indirect defenses against insect pests. However, little is known about the priming mechanism of key volatiles in wheat. To determine whether and how plant volatile induced defense priming in wheat against the grain aphid Sitobion avenae, a combination of insect bioassays, phytohormone and defense metabolite quantification, and transcriptome analyses were performed using an important aphid damage-induced plant volatile, methyl salicylate (MeSA). MeSA treatment primed wheat for enhanced accumulation of salicylic acid, flavonoid and benzoxazinoids (BXs), and increased resistance to S. avenae and attractiveness to an aphid parasitoid Aphelinus asychis. Supplementation with a BX (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one) and two flavonoids (xanthohumol and isobavachalcone) in artificial diet impaired the survival, development and fecundity of S. avenae. Moreover, MeSA treatment induced wheat volatile emission especially MeSA. Functional investigation of odorant-binding proteins (OBPs) in A. asychis revealed that AasyOBP4 is responsible for the recognition of MeSA. Taken together, our results provide insights into the molecular mechanism of MeSA-mediated defense in wheat and propose MeSA as a phytoprotectant for crop protection and sustainable agriculture.

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.

Transcriptomic analysis of male diamondback moth antennae: Response to female semiochemicals and allyl isothiocyanate

Female semiochemicals and allyl isothiocyanate (AITC) attract moths, and the moths use odorant-degrading enzymes (ODEs) to break down the excess odor. By identifying antennae-specific ODEs, researchers have established the molecular foundation for odorant degradation and signal inactivation in insects. This enables further exploration of new pest control methods. Currently, the degradation of female semiochemicals and AITC has received limited attention, inspiring this study to identify target ODEs in diamondback moths through transcriptome analysis. Sequencing of antennae from male adults (MA) exposed to female adults (FA) and AITC yielded a substantial 54.18 Gb of clean data, revealing 2276 differentially expressed genes (DEGs) between the MA and MA-FA treatments, and 629 DEGs between MA and MA-AITC treatments. The analysis of MAs exposed to FAs and AITC identified 29 and 17 ODEs, respectively, mainly involving aldehyde dehydrogenases (ALDHs), alcohol dehydrogenases (ADs), cytochrome P450s (CYPs), and UDP-glucuronosyltransferases (UGTs). Pathway analysis revealed primary enrichment in glycolysis/gluconeogenesis and fatty acid degradation in female adult treatments. In contrast, AITC treatments showed major enrichment in pathways related to pentose and glucuronate interconversions, retinol metabolism, and ascorbate and aldarate metabolism. Additionally, qRT-PCR analysis validated the expression patterns of 10 ODE genes in response to these treatments, with varying results observed among the genes. These findings indicate significant changes in ODE expression levels, providing a molecular foundation for identifying potential targets for behavioral inhibitors.