Odorant-Binding Protein 3-Oriented Rational Design and Discovery of Novel Jasmonate Derivatives as Potential Aphid-Repellent Agents

Discovery of novel skeletons of aphid repellents based on the key fragment of nepetalactone and plant volatiles

BACKGROUND

Aphids are significant agricultural pests, causing extensive crop damage and transmitting plant viruses. Conventional insecticide-based pest control faces challenges such as human and environmental toxicity and resistance. As alternative solutions, pheromone-based repellents have emerged as a promising approach. However, the instability of key compounds like (E)-β-Farnesene (EBF) has limited their effectiveness in field applications. To address these limitations, this study focuses on developing novel aphid repellent compounds based on plant volatiles and nepetalactone key fragments.

RESULTS

In this study, a series of derivatives were designed and synthesized from the lead compound (±)I by incorporating plant volatiles, leading to the discovery of two novel compounds with new skeletons, IV-13 and IV-4. Through further modifications of the ring size and the alkyl substitutions, two optimized structures, compounds IV-30 and IV-36, were identified, demonstrating promising aphid repellent activities. Bioassays indicated that IV-30 (RV = 85.2%) and IV-36 (RV = 70.3%) exhibited significantly enhanced repellent properties compared to their precursor compounds. Molecular docking studies revealed strong binding interactions of these compounds with aphid odorant-binding protein 3(OBP3), providing further evidence of their improved biological efficacy.

CONCLUSION

The introduction of novel structures such as compounds IV-30 and IV-36 based on nepetalactone and plant volatile fragments resulted in the discovery of novel promising para-pheromones for aphid control. These compounds exhibit stable and effective repellent activities, providing a solid foundation for further development of synthetic aphid repellents in integrated pest management strategies. © 2025 Society of Chemical Industry.

Structural Optimization of Aphid Repellents Based on the Low-Energy Conformation of (E)-β-Farnesene

Aphids cause significant agricultural damage, prompting the search for eco-friendly control methods. Although pheromones offer a natural alternative to synthetic insecticides, the low stability of aphid alarm pheromones limits their use. To develop more stable repellents, we computed the low-energy conformations of (E)-β-farnesene (EBF), revealing five conformations with a conserved spatial region, and used these insights to modify the para-pheromone IV-30. Molecular superimposition confirmed that IV-30 mimics EBF's conformations. A series of analogues were synthesized, and experiments showed that an ester group on the six-membered ring's left side is crucial for repellent activity, while electron-rich groups on the right side enhance it. Notably, compound V-9 demonstrated repellent efficacy comparable to EBF, deepening the understanding of structure-activity relationships and supporting the development of novel aphid repellents for integrated pest management.

Targeting Two Odorant-Binding Proteins in Acyrthosiphon pisum: Discovery of Novel Jasmone Derivatives as Aphid Repellents

Odorant-binding proteins (OBPs) are potential targets for the discovery of insect behavior regulators. Cis-jasmone (CJ) was first identified as a repellent against Acyrthosiphon pisum (A. pisum) by its binding to ApisOBP3 and ApisOBP7. Therefore, twenty-one novel CJ derivatives were designed and synthesized based on the binding pockets of these two ApisOBPs. Almost all derivatives showed better binding affinities to ApisOBPs and aphid-repellent activities than CJ, respectively. The representative derivative 6bg had the most significant binding affinities to ApisOBP3 and ApisOBP7 with Ki values of 6.95 μM and 4.81 μM, respectively. Moreover, 6bg had the highest repellent rate of 71.62% against A.pisum at a dose of 5 μg and also elicited a dose-dependent electroantennography response. The binding mechanism revealed that hydrophobic interactions generated by nonpolar residues in ApisOBP3 and ApisOBP7 were key to the binding. This study offers insights into the rational design of novel aphid repellents targeting two OBPs.

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.

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.

Sustainable Natural Resources for Aphid Management: β-Ionone and Its Derivatives as Promising Ecofriendly Botanical-Based Products

β-Ionone, sustainably derived from Petunia hybrida as a natural bioresource, was identified as a lead compound for integrated aphid management. A series of β-ionone derivatives containing ester groups were designed and synthesized for the purpose of discovering renewable botanical-based products. The odorant-binding protein (OBP) binding test indicated that β-ionone and its derivatives displayed binding affinities with Acyrthosiphon pisum OBP9 (ApisOBP9) and Harmonia axyridis OBP15 (HaxyOBP15). Bioactivity assays revealed that most β-ionone derivatives exhibited a higher repellent activity than that of β-ionone. β-Ionone and derivatives 4g and 4l displayed attractiveness to H. axyridis. Specifically, 4g was a highly promising derivative, possessing good repellent activity against A. pisum and attractiveness to H. axyridis. Molecular dynamics simulations revealed that integrating the hydrophobic ester group into the β-ionone framework strengthened the van der Waals interactions of 4g with ApisOBP9/HaxyOBP15, improving the binding affinity with OBPs and producing higher push-pull activity than β-ionone; 4g also had low toxicity toward nontarget organisms. Thus, 4g is a potential ecofriendly, botanical-based option for aphid management.

Expression Pattern of RpCSP6 from Rhopalosiphum padi and Its Binding Mechanism with Deltamethrin: Insights into Chemosensory Protein-Mediated Insecticide Resistance

The mechanisms of insecticide resistance are complex. Recent studies have revealed a novel mechanism involving the chemosensory system in insecticide resistance. However, the specific binding mechanism between olfactory-related genes and insecticides needs to be clarified. In this study, the binding mechanism between pyrethroid insecticide deltamethrin and RpCSP6 from Rhopalosiphum padi was investigated by using computational and multiple experimental methods. RpCSP6 was expressed in different tissues and developmental stages of R. padi and can be induced by deltamethrin. Knockdown of RpCSP6 significantly increased the susceptibility of R. padi to deltamethrin. The binding affinity of RpCSP6 to 24 commonly used insecticides was measured. Seven key residues were found to steadily interact with deltamethrin, indicating their significance in the binding affinity to the insecticide. Our research provided insights for effectively analyzing the binding mechanism of insect CSPs with insecticides, facilitating the development of new and effective insecticides that target insect CSPs.

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.

Ligand binding properties of three odorant-binding proteins in striped flea beetle Phyllotreta striolata towards two phthalate esters

Odorant-binding proteins (OBPs) initiate insect olfactory perception and mediate specific binding and selection of odorants via uncertain binding mechanisms. We characterized the binding characteristics of four OBPs from the striped flea beetle Phyllotreta striolata (SFB), a major cruciferous crop pest. Tissue expression analysis revealed that the two ABPII OBPs (PstrOBP12 and PstrOBP19) were highly expressed mainly in the antenna, whereas the two minus-C OBPs (PstrOBP13 and PstrOBP16) showed a broad expression pattern. Competitive binding assays of cruciferous plant volatiles showed that PstrOBP12, PstrOBP16 and PstrOBP19 had very strong binding capacities for only two phthalate esters (Ki < 20 μM), and PstrOBP13 specifically bound to four aromatic volatiles (Ki < 11 μM). Fluorescence quenching assays displayed that two phthalate esters bound to three PstrOBPs via different quenching mechanisms. PstrOBP12/PstrOBP16-diisobutyl phthalate and PstrOBP19-bis(6-methylheptyl) phthalate followed static quenching, while PstrOBP12/PstrOBP16-bis(6-methylheptyl) phthalate and PstrOBP19-diisobutyl phthalate followed dynamic quenching. Homology modelling and molecular docking displayed that PstrOBP12-diisobutyl phthalate was driven by H-bonding and van der Waals interactions, while PstrOBP16-diisobutyl phthalate and PstrOBP19-bis(6-methylheptyl) phthalate followed hydrophobic interactions. Finally, behavioural activity analysis demonstrated that phthalate esters exhibited different behavioural activities of SFB at different doses, with low doses attracting and high doses repelling. Overall, we thus revealed the different binding properties of the three PstrOBPs to two phthalate esters, which was beneficial in shedding light on the ligand-binding mechanisms of OBPs.

Discovery and properties of novel analogues of the aphid pheromones nepetalactone and nepetalactol

BACKGROUND

Pheromones have unique advantages for pest control. Current aphid pheromone research focuses on alarm and sex pheromones. However, practical applications are limited so far, as (E)-β-farnesene has only been investigated to a small extent as an alarm pheromone and only male aphids are targeted by sex pheromones. Previous literature reports electrophysiological responses and repellent behavior of asexual aphids to nepetalactone (1B), therefore our objective was to modify nepetalactone's structure to identify key fragments responsible for repellent effects, as guidance for subsequent modifications and further investigation.

RESULTS

In this study, seven derivatives were designed and synthesized based on nepetalactol (1A) and nepetalactone (1B) as lead compounds. Free-choice tests, conducted using cowpea aphids (Aphis craccivora), revealed that the lactone moiety was crucial for the repellent activity, and the removal of the carbonyl group eliminated the repelling effect. Compound (±)1I, an analogue of nepetalactone (1B), demonstrated a significantly higher repellent value than nepetalactone (1B) at three different concentrations, and even at 0.1 mg/mL it maintained a considerable repellent effect (26.5%). Electrostatic potential and density functional theory calculations supported the importance of the carbonyl group for the repellent effects.

CONCLUSION

The newly discovered para-pheromone (±)1I shows improved repellent effects and potential for development as a novel biological control agent. Based on our innovative findings, analogues with improved efficacy and properties can be designed and prepared. Our research contributes to understanding the effects of structural modifications on pheromone activity and properties, which is crucial for exploring novel pheromone-based products for crop protection. © 2024 Society of Chemical Industry.

Development of Sustainable Insecticide Candidates for Protecting Pollinators: Insight into the Bioactivities, Selective Mechanism of Action and QSAR of Natural Coumarin Derivatives against Aphids

Plants employ abundant toxic secondary metabolites to withstand insect attack, while pollinators can tolerate some natural defensive compounds. Coumarins, as promising green alternatives to chemical insecticides, possess wide application prospects in the crop protection field. Herein, the bioactivities of 30 natural coumarin derivatives against Aphis gossypii were assessed and revealed that 6-methylcoumarin exhibited potent aphicidal activity against aphids but displayed no toxicity to honeybees. Additionally, using biochemical, bioinformatic, and molecular assays, we confirmed that the action mode of 6-methylcoumarin against aphids was by inhibiting acetylcholinesterase (AChE). Meanwhile, functional assays revealed that the difference in action site, which located in Lys585 in aphid AChE (equivalent to Val548 in honeybee AChE), was the principal reason for 6-methylcoumarin being toxic to aphids but safe to pollinators. This action site was further validated by mutagenesis data, which uncovered how 6-methylcoumarin was unique selective to the aphid over honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established, revealing that the central structural feature was H3m, which offers guidance for the future design of more potent coumarin compounds. This work provides a sustainable strategy to take advantage of coumarin analogues for pest management while protecting nontarget pollinators.