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Article

Plant Volatile Organic Compounds Attractive to Monolepta signata (Olivier)

by
Lun Li
1,2,
Jiyu Cao
1,
Zhiping Cai
1,* and
Jing Chen
1,*
1
Key Laboratory of Oasis Agricultural Pest Management and Plant Protection Resources Utilization, College of Agriculture, Shihezi University, Shihezi 832000, China
2
Institute of Plant Protection, Xinjiang Uygur Autonomous Region Academy of Agricultural Sciences/Key Laboratory of Integrated Pest Management on Crops in Northwestern Oasis, Ministry of Agriculture and Rural Affairs/Xinjiang Key Laboratory of Agricultural Biosafety, Urumqi 830091, China
*
Authors to whom correspondence should be addressed.
Insects 2025, 16(12), 1233; https://doi.org/10.3390/insects16121233
Submission received: 19 September 2025 / Revised: 2 December 2025 / Accepted: 4 December 2025 / Published: 6 December 2025
(This article belongs to the Section Insect Pest and Vector Management)
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Simple Summary

Monolepta signata (Olivier) is a beetle that damages important crops in East Asia, such as cotton and corn. Traditional control methods rely heavily on chemical pesticides, which can harm the environment and cause pest resistance. In this study, we explored whether plant volatiles, natural smells released by plants, could be used to attract beetles. We created 26 different scent mixtures using common plant odors and tested how the beetles reacted to them in the laboratory and the field. Some mixtures were very attractive to the beetles, particularly those containing three different odors. One mixture, made from α-phellandrene, trans-2-hexen-1-ol, and 1-heptene, attracted the most beetles in field traps. Our findings suggest that plant-based scent mixtures can be developed as safer and more sustainable ways to monitor or control this pest, without relying on harmful pesticides.

Abstract

Plant volatiles play a critical role in mediating insect host location behavior and offer eco-friendly alternatives for chemical control. Monolepta signata is a widespread phytophagous pest in East Asia that poses a significant threat to various crops. In this study, we evaluated the electrophysiological and behavioral responses of adult M. signata to 26 binary and ternary mixtures of 13 plant-derived volatile compounds extracted from cotton and corn leaves. Electroantennogram (EAG) recordings revealed that females exhibited the strongest responses to mixtures 20, 23, and 12, whereas males were the most responsive to mixtures 26, 19, and 4. Y-tube olfactometer assays showed significant behavioral attraction of females to mixtures 1, 20, 23, and 26, and males to mixtures 19, 22, and 23. Field trials demonstrated that mixtures 22, 23, and 26 attracted significantly more adults than the control, with mixture 23 (α-phellandrene + trans-2-hexen-1-ol + 1-heptene) achieving the highest trap capture. These findings highlight the potential of specific volatile blends, especially ternary mixtures, as effective attractants of M. signata, and support their application in environmentally sustainable pest monitoring and management strategies.

Graphical Abstract

1. Introduction

Plants release a wide variety of volatile organic compounds (VOCs) from their leaves, flowers, and fruits as part of their interactions with the environment [1]. Plant VOCs are low-molecular-weight, highly volatile chemicals released into the atmosphere, which disperse rapidly and serve as key cues for herbivorous insects [2,3]. More than 1700 volatile compounds have been identified in over 90 plant families, including hydrocarbons, alcohols, aldehydes, ketones, esters, organic acids, and terpenes. This represents a wide diversity of plant-derived secondary metabolites [4]. Numerous studies have demonstrated that plant volatiles can significantly influence insect behavior, such as host location, mating, and oviposition [5,6,7,8]. Several studies have shown that host-derived volatiles can effectively attract phytophagous pests, and can be applied to the management of agricultural and forestry pests such as Ectropis obliqua, Empoasca onukii, and Adelphocoris species [9,10,11].
Monolepta signata (Olivier, 1808) (Coleoptera: Chrysomelidae) is a herbivorous agricultural pest widely distributed in China [12,13]. This insect feeds directly on the leaves of the host plants, and its host range includes various plant families such as Gramineae, Malvaceae, Leguminosae, Cruciferae, Rosaceae, Ulmaceae, and Salicaceae. It mainly affects cotton, corn, rice, sorghum, and potatoes, leading to reduced crop yields [14]. It was first reported in the Xinjiang Uygur Autonomous Region in the late 1990s and has since caused significant damage and economic losses to major crops such as cotton and corn, becoming one of the most important agricultural pests in the region [15,16,17]. Currently, chemical treatment is the primary strategy for controlling M. signata; however, this has led to problems such as resistance, food safety concerns, and environmental pollution [18]. Therefore, there is an urgent need to reduce the use of pesticides, develop environmentally friendly measures to control adult pests in fields, and protect crops from M. signata infection.
An effective semiochemical lure for population monitoring is important in integrated pest management (IPM) [19]. Consequently, the identification of bioactive compounds from host plants is crucial for understanding host selection behavior and olfactory function in phytophagous insects, and it is crucial to develop effective host plant volatile attractants [20]. Insects rely on highly sensitive olfactory systems to detect plant volatiles and use these systems to locate suitable hosts. Previous studies have shown that the antennae of M. signata contain 114 olfactory-related genes and seven types of sensilla, three of which exhibit porous structures associated with semiochemical perception [21,22]. These volatiles are typically released as complex blends, and most insects respond to a mixture rather than single compounds for accurate host recognition [6,23,24,25,26]. Aulacophora foveicollis females respond positively to volatile blends of Solena amplexicaulis fruit because of the synergistic action of nonanal and (E, Z)-2, 6-nonadienals [27]. Vine weevil adults are attracted to a mixture of seven plant volatiles, although either no responses or negative responses were recorded for each of these compounds when presented individually [28]. For volatiles in the seeds of four legume varieties, the attraction effect on the important leguminous insect pest Callosobruchus maculatus was significantly enhanced when these compounds were formulated in various proportion [29]. Cis-3-hexen-1-ol from tobacco plants induces oriented flight in Phthorimaea operculella, whereas nonanal, decanal, decane, methyl hexadecanoate, and related volatiles stimulate oviposition in female adults [30]. Therefore, it is important to study the effects of mixed components in host plants on insect behavior [20].
Previous studies have demonstrated that under laboratory conditions, both the type and concentration of individual VOCs can influence the behavior of M. signata. Among the various plant volatiles, peppermint essential oil exhibited the strongest repellent effect, with a repellency rate of 74%, whereas geraniol showed the strongest attractive effect, with a luring rate of 70% [31]. In a study involving seven cotton and corn derived volatiles, M. signata females were attracted to β-ionone at a concentration of 10 μg/mL; however, they were repelled by γ-terpinene and caryophyllene oxide. In contrast, males were attracted by γ-terpinene and D-limonene; however, they were repelled by β-ionone [32]. In our previous studies, Dragosantol and α-pinene from cotton and corn leaves were identified to have significant attraction to M. signata adults [33]. Currently, we have detected 1-heptene, aromadendrene, trans-2-hexen-1-ol, α-phellandrene, α-caryophyllene, and hexadecene from cotton leaves, α-farnesene and heptadecane from corn leaves, and common β-ocimene, trans-2-hexenal-al, (Z)-3-hexen-1-ol (leaf alcohol), β-pinene, nerolidol, and 3-methylpentanal from cotton and corn leaves using GC-MS (unpublished data). Several studies have shown that a mix of host volatile species in the field is more effective in attracting insects than a single host volatile [34,35,36]. However, few studies have investigated the behavioral responses of mixed components in host plants to M. signata, and there is limited research on the use of plant volatiles to attract M. signata for large-scale biological control in the field.
Although several plant volatiles have been found to elicit electrophysiological or behavioral responses in M. signata under laboratory conditions, little is known about the effects of volatile blends on this species. To fill this knowledge gap, this study aimed to (1) evaluate the electrophysiological and behavioral responses of M. signata adults to 26 mixtures of plant volatiles using electroantennogram (EAG) recordings and Y-tube olfactometer assays, and (2) identify the most attractive blends for potential application in field trapping systems.

2. Materials and Methods

2.1. Insects

M. signata adults were collected from cotton fields in Shihezi City, Xinjiang Uygur Autonomous Region, China (44°32′85″ N; 85°98′33″ E). The fields are sparsely surrounded by weeds. The collected adults were reared on fresh cotton leaves in growth chambers set at 25 ± 1 °C, 50–70% relative humidity, 2000 lx light intensity, and a 16:8 h light: dark photoperiod.

2.2. Chemicals

The standard chemical samples used in this study are listed in Table 1.

2.3. Preparation of Plant Volatile Mixtures

The nine VOCs used in this study were selected from the 14 volatiles previously identified in cotton leaves (Gossypium hirsutum) and corn leaves (Zea mays) by headspace collection and GC–MS analysis (unpublished data). Compounds were selected based on their consistent detection in both host plants and their reported electrophysiological or behavioral activities in Coleopteran species. In the preliminary experiments, all 14 compounds were tested in EAG dose–response assays with M. signata, and the nine compounds that elicited the strongest responses at their optimal concentrations selected for subsequent experiments (Figure S1).
Nine VOCs, namely, alcohols, aldehydes, terpenoids, and hydrocarbons, were classified according to their major functional categories. Following previously reported attractant formulation strategies [25], mixtures were designed by combining compounds with different functional groups (e.g., alcohol + aldehyde, terpene + aldehyde + hydrocarbon) to explore potential additives or synergistic effects. To ensure that each compound in a mixture reached its individually determined optimal EAG concentration, each individual compound was first diluted in liquid paraffin to an appropriate stock concentration. Binary and ternary mixtures were then prepared by combining equal volumes of the appropriately concentrated stocks so that the final concentration of each compound in the mixture equaled its optimal EAG concentration (10 μL/mL or 1 μL/mL). All mixtures were freshly prepared immediately prior to behavioral and electrophysiological assays (Table 2).

2.4. Determination of EAG Responses of M. signata to Mixtures of Plant Volatiles

The EAG responses of M. signata were recorded using an EAG detection system following the method described by Liu [31]. The system of EAG, including IDAC-2, CS-55, EAG probe (Syntech, Hilversum, The Netherlands), Faraday cage, and recording software, was named GC-EAD (version 1.2.5). Before each test, the sex of the adult M. signata was identified and the individuals were starved for at least 4 h. The airflow system was then checked to ensure normal operation, and it was confirmed that the distilled water in the humidifying bottle did not enter the airflow lines. For each compound or mixture, 20 μL was applied in a “Z” shape onto a filter paper strip (length 50 mm, width 5 mm), which was then inserted into a Pasteur pipette. Each Paster tube was used only once to test each compound. A humidified airflow of 500 mL/min was directed through a pipette and positioned 1 cm from the antenna. The stimulus was delivered at 100 mL/min for 1 s, with an interval of at least 60 s between stimulations to prevent adaptation. N-hexane served as the reference, and liquid paraffin was used as the control. The test sequence was as follows: liquid paraffin, n-hexane, test volatile mixture, n-hexane and liquid paraffin. Each mixture was tested in numerical order, and the responses were recorded from six different antennae per treatment. To minimize variation, only active and undamaged adult M. signata were selected for testing. Each volatile mixture was tested using six biological replicates, with one antenna per beetle. None of the antennas were used more than once. All tests were conducted between 25 ± 1 °C from 10:00 to 20:00.

2.5. Bioassay of Behavioral Response of M. signata to Mixtures of Plant Volatiles

The behavioral responses of M. signata adults to plant volatile mixtures were evaluated using a glass Y-tube olfactometer. The olfactometer consisted of a main glass tube (1.5 cm; length: 15 cm) with two arms (10 cm each) that diverged at an angle of 70°. Each arm was connected to a glass odor source chamber via Teflon tubing. The apparatus was illuminated by two 20 W fluorescent lamps (light intensity: 2000 lx) and maintained under controlled environmental conditions (25 ± 1 °C, 60 ± 5% RH). Constant airflow (200–300 mL/min, LZB-3WB, Changzhou Kede thermal instrument Co., Ltd., Changzhou, China) was provided by two atmospheric samplers (QC-1S, Scientific Institute of Labour Protection, Beijing, China) through a drying tower (250 mL) filled with activated charcoal. For each assay, 20 μL of a volatile mixture was applied to a filter paper strip and placed in one odor source bottle, while the other bottle contained a strip treated with an equal volume of liquid paraffin (control). All Y-tube bioassays were conducted in a dedicated insect behavioral laboratory under odor-controlled conditions. The experimenter remained outside the airflow path during the tests to prevent odor contamination.
To minimize variation, only active and undamaged adults of M. signata were selected for testing. Individual adults were starved for at least 4 h before the bioassay, then placed at the base of the Y-tube olfactometer for observation for a 10 min period. A choice was recorded when an insect entered a branch tube by more than two-thirds of its length and remained there for at least 30 s, otherwise, it was recorded as “no choice.” The odor-source positions were switched every five insects to prevent positional bias, and a new Y-tube was used every 10 insects. Eighty female and 80 male M. signata adults were tested in each treatment, and each was used only once. All assays were conducted at 25 ± 1 °C from 10:00 to 20:00.

2.6. Field Attraction

The field trial was conducted in an 8 hm2 cotton field in Shihezi, Xinjiang Uygur Autonomous Region, China, during the flowering stage when M. signata adults were predominant. The field population density was estimated from the control traps, with three traps (15 m apart) capturing an average of approximately three adults per trap over the 14-day survey period. New moth traps equipped with polyethylene sustained-release bottles (Beijing Zoje Sifang Biotechnology Co., Ltd., Beijing, China) were used. Each mixture (1 mL) was loaded into identical polyethylene slow-release bottles (wall thickness 0.8 mm, mouth diameter, 7 mm) to standardize evaporation conditions among treatments, while control traps contained the same volume of liquid paraffin. The traps were suspended slightly above the cotton canopy, with a minimum distance of 15 m between adjacent traps. A randomized complete block design was used, with three independent blocks established within a single 8 hm2 cotton field. Each block contained all treatments, and the blocks were separated by more than 50 m to ensure independent replicates and to minimize cross-interference among the volatile sources. The number and sex of M. signata adults captured were recorded every two days throughout the trapping period. Sex identification was performed under a stereomicroscope based on the abdominal morphology, and all captured individuals were removed after each count. No pesticides were used during the experimental period.

2.7. Data Analyses

The EAG response of M. signata to plant-derived volatile mixtures was calculated using the following formula:
A = (B − C)/(D − C) × 100%,
where A is the relative EAG response to a given stimulus; B is the raw EAG amplitude in response to the stimulus; C is the mean EAG response to liquid paraffin (recorded before and after the stimulus); and D is the mean EAG response to n-hexane (recorded before and after the stimulus) [37]. Differences in EAG responses among treatments were analyzed using one-way analysis of variance (ANOVA), followed by least significant difference (LSD) multiple range tests for post hoc comparisons. Differences between the male and female EAG responses in the same mixture were analyzed using an independent samples t-test.
For behavioral assays, the null hypothesis assumed no preference by M. signata adults for either arm of the olfactometer (i.e., a 1:1 distribution of responses). This was tested using chi-square (χ2) goodness-of-fit tests, excluding non-responding individuals. Bonferroni adjusted p-values are also provided as references. Both raw and adjusted p-values are reported.
Trap capture data from the field experiments were also analyzed using one-way ANOVA to assess the effects of the different volatile mixtures. All statistical analyses were performed using SPSS software (version 20.0; SPSS Inc., Chicago, IL, USA).

3. Results

3.1. Electroantennogram Responses of M. signata to Plant Volatile Mixture

The EAG amplitudes of female M. signata to the 26 plant-derived mixtures differed significantly among some treatments (Figure 1). Mixture 20 elicited the strongest response (3.076 ± 0.251 mV), followed by mixtures 23 (2.764 ± 0.188 mV) and 12 (2.534 ± 0.369 mV). Eight mixtures (1, 4, 12, 20, 22, 23, 25, and 26) elicited responses greater than 1.905 mV and were therefore selected as candidate attractants for subsequent behavioral assays (Figure 1).
Similarly, males showed the highest response to mixture 26 (2.861 ± 0.449 mV), followed by mixtures 19 (2.843 ± 0.233 mV) and 4 (2.652 ± 0.175 mV). Eight mixtures (4, 8, 19, 20, 22, 23, 24, and 26) elicited responses greater than 1.874 mV, and were chosen as candidate attractants for behavioral evaluation. Notably, mixtures 4, 20, 22, 23, and 26 elicited consistently strong responses in both sexes and were, therefore, considered key candidates for further analysis (Figure 2).
Both male and female antennae responded to all tested mixtures, with varying response amplitudes. There were no significant differences in the EAG responses between males and females for most mixtures (p > 0.05), except for mixtures 1 (F = 2.547, df = 10, p = 0.014), 2 (F = 2.477, df = 10, p = 0.019), 3 (F = 0.017, df = 10, p = 0.021), 5 (F = 5.711, df = 10, p = 0.023), 8 (F = 3.346, df = 10, p = 0.012), 10 (F = 0.162, df = 10, p = 0.003), 11 (F = 0.208, df = 10, p = 0.015), 14 (F = 0.130, df = 10, p = 0.029), 15 (F = 1.193, df = 10, p = 0.035), 19 (F = 0.001, df = 10, p = 0.003), 23 (F = 0.081, df = 10, p = 0.006), and 25 (F = 0.595, df = 10, p = 0.090), which showed significant sex-based differences (Figure 1 and Figure 2).

3.2. Behavioral Responses of M. signata to Mixtures of Plant Volatiles

Eight plant-derived attractants screened using EAG were further evaluated in olfactory behavioral assays with M. signata. In females, formulations 1 (χ2 = 3.981, p = 0.046), 20 (χ2 = 5.055, p = 0.025), 23 (χ2 = 5.726, p = 0.016), and 26 (χ2 = 6.248, p = 0.012) elicited significant attraction (p < 0.05), with response rates of 65.79%, 67.50%, 68.83%, and 69.86%, respectively. Although formulation 1 did not remain significant after Bonferroni correction (adjusted p = 0.067), it still exhibited a consistent trend of attraction (Table 3). Among all formulations, formulation 26 showed the strongest response. In contrast, formulations 4 (χ2 = 0.908, p = 0.341), 12 (χ2 = 1.333, p = 0.248), 22 (χ2 = 1.171, p = 0.279), and 25 (χ2 = 1.126, p = 0.298) did not produce significant effects (p > 0.05) (Figure 3).
In males, significant attraction was observed for formulations 19 (χ2 = 4.244, p = 0.039), 22 (χ2 = 6.061, p = 0.014), and 23 (χ2 = 4.144, p = 0.042), with response rates of 66.23%, 69.23%, and 66.22%, respectively; formulation 22 showed the highest response. Although formulations 19 and 23 did not remain significant after Bonferroni correction (adjusted p = 0.058 and 0.061), they still exhibited a consistent trend of attraction (Table 3). No significant effects were detected for formulations 4 (χ2 = 1.126, p = 0.289), 8 (χ2 = 0.253, p = 0.615), 20 (χ2 = 0.805, p = 0.370), 24 (χ2 = 0.187, p = 0.666), and 26 (χ2 = 2.522, p = 0.112) (p > 0.05) (Table 3, Figure 4).

3.3. Evaluation of the Field Level Trapping

The trapping efficacy of the six plant-derived attractants against M. signata adults showed an initial increase followed by a decline. Mixtures 1, 19, 22, 23, and 26 peaked on 16 July, whereas formulation 20 peaked on 18 July. Mixtures 22 and 23 captured significantly more adults than the control on 16 July, while mixtures 20 and 26 captured more adults on 18 July (p < 0.05). Notably, only mixture 23 maintained significant attractiveness on 24 July (Table 4).
Field trials demonstrated that mixtures 22, 23, and 26 captured significantly more M. signata adults than the control (p < 0.05), with mixture 23 showing the highest capture (17.7 ± 4.1 adults per lure), followed by mixtures 26 (14.0 ± 2.1) and 22 (13.7 ± 2.2). In contrast, mixtures 1, 19, and 20 did not differ significantly from the control (p > 0.05; Figure 5).
Both female and male M. signata adults were captured by all the mixtures, however females were trapped in significantly higher numbers than males (Figure S2). Mixture 23 had the highest female catch and overall attractiveness, followed by mixtures 1 and 26. Mixture 1 attracted significantly more females than males (p < 0.05), whereas no significant sex-related differences were observed with the other five volatile plant mixtures.

4. Discussion

In this study, we identified specific plant-derived volatile mixtures that elicit strong antenna and behavioral responses in M. signata, and demonstrated that several of these blends, particularly ternary formulations, also exhibit practical attractiveness under field conditions. These findings indicate that M. signata may rely on complex host–plant volatile combinations rather than simple two-component combinations, underscoring the ecological importance of blend synergy in host–location behavior. Most insects detect complex volatile blends emitted by host plants via their antennae, and M. signata similarly possesses abundant olfactory receptors and antennal sensilla that enable the detection of such cues [21,22,38]. Although our use of six antennae per treatment follows common practice in EAG studies [37], future work could benefit from increased replication and from testing multiple concentrations of each volatile mixture to better assess dose-dependent effects. In behavioral assays, the mixture 26 (trans-2-hexen-1-al + 1-heptene + trans-2-hexen-1-ol) was most attractive to females, followed by mixture of 23 (α-phellandrene + trans-2-hexen-1-ol + 1-heptene), mixture of 20 (leaf alcohol + trans-2-hexen-1-ol + 1-heptene), and mixture of 1 (β-pinene + leaf alcohol). For males, the most attractive was mixture 22 (β-pinene + trans-2-hexen-1-al + leaf alcohol), followed by mixture 19 (β-pinene + α-phellandrene + trans-2-hexen-1-al), and mixture 23 (α-phellandrene + trans-2-hexen-1-ol + 1-heptene). These results indicate that specific mixtures can elicit sex-specific behavioral responses, highlighting the potential to optimize attractant formulations for targeted monitoring or management of M. signata in the field. Previously reported single-compound attractants such as geraniol achieved an attraction rate of 64 ± 8.94% at concentrations of 10−1 mol·L−1 [31], which is lower than the attraction rates obtained for the mixtures formulated in this study (mixtures 1, 19, 20, 22, 23, and 26). This difference may be related to the concentrations and release dynamics of the volatiles used [33]. Overall, ternary mixtures consistently outperformed binary combinations, supporting previous findings that multicomponent blends are more effective at attracting insects than single or dual compounds [34,35,36]. This may be because insects rely on the antennal detection of complex volatile profiles as environmental cues that guide their host-seeking behavior [28,37].
This study also revealed sex-specific differences in both the EAG and behavioral responses of M. signata adults to the same volatile mixtures. In the field trials, females were captured in higher numbers than males for all mixtures, except mixtures 19 and 22. Although the same volatiles were tested, males and females often exhibited different EAG responses [39], as reported for Brontispa longissima [40] and Monochamus alternatus [41]. A similar pattern was observed in M. signata, where sex-specific responses to identical volatile mixtures likely reflect divergent reproductive strategies and dietary requirements, particularly in host location and oviposition [42]. These findings further indicate that insect olfactory systems are sufficiently sophisticated to detect subtle variations in plant volatile profiles under natural conditions [38]. In addition, the behavioral responses of male and female M. signata suggested that modifying a single component within a volatile blend may influence its attractiveness, a phenomenon also noted in previous studies [43,44,45]. In our assays, trans-2-hexen-1-ol and 1-heptene appeared to be the key compounds driving female attraction, with leaf alcohol, α-phellandrene, trans-2-hexen-1-al, and β-pinene serving as secondary enhancers. In contrast, β-pinene and trans-2-hexen-1-al likely played primary roles in male attraction, while α-phellandrene and leaf alcohol may act as supporting contributors. Such primary compounds are often indispensable for insect attraction because their replacement typically abolishes the response, whereas altering the secondary components tends to diminish it, which is consistent with the observations of Thöming and Knudsen [46]. These findings highlight the importance of disentangling the roles of individual and combined volatiles, which is essential for identifying key attractants and developing environmentally friendly tools for pest monitoring and control [47]. However, as field-collected adults of unknown age and mating status were used in this study, these factors may have contributed to individual variations in antennal or behavioral responses [48]. Future studies using laboratory-reared insects under standardized physiological conditions will improve the comparability and reproducibility of the results.
In the field-trapping experiment, the attractiveness of all six mixtures declined over time, which is consistent with the typical release pattern of field attractants [30,49,50]. Among them, the mixture 23 (α-phellandrene + trans-2-hexen-1-ol + 1-heptene) tended to attract more insects on average. During the penultimate field survey, only mixture 23 showed a significantly higher trap catch than the control, suggesting that it may have maintained attractiveness longer than the other mixtures under the tested conditions. The release rates of the mixtures were not measured directly, which limited the precise interpretation of their relative effectiveness. Future work will aim to quantify the release profiles of each formulation to improve field evaluation accuracy. Our results showed that although some mixtures, such as mixture 20, elicited strong electroantennographic and behavioral responses in the laboratory, their field attractiveness was much weaker. This discrepancy suggests that EAG and behavioral responses alone may not fully reflect host selection behaviors under natural conditions [51,52]. The discrepancies observed between the laboratory and field results may have occurred due to differences in environmental and ecological conditions. In laboratory olfactometers, insects are exposed to pure, high-concentration odor streams without competing stimuli, whereas in the field, the presence of abundant background volatiles from natural hosts, fluctuating wind direction, temperature, and humidity can dilute or mask synthetic odors [9]. Moreover, odor release dynamics and blend ratios may differ between laboratory dispensers and field traps, leading to altered perceptions or behavioral responses [10]. Similar inconsistencies between laboratory and field performance have been widely reported in chemical ecology studies [48,53].
Environmental variables such as blend concentration, background odors, temperature, humidity, and surrounding vegetation further influence the attractiveness of volatiles in the field [53,54]. In the present field trials, these parameters remained relatively stable (26–32 °C, 50–70% RH, <1.5 m/s wind), yet even small fluctuations could affect volatile release rates and insect activity [50]. Therefore, although our results reflect typical summer conditions in the cotton fields, they should be interpreted with caution. The nine volatiles used in this study were originally identified in both cotton and corn leaves. However, since field validation was performed only in cotton, additional experiments in corn fields are needed to confirm whether the observed behavioral patterns are consistent across different host habitats. Future studies should focus on optimizing lure release rates, trap design, and placement, as well as refining release devices and formulations to maintain stable volatile emissions under field conditions [10,20]. To the best of our knowledge, no commercial attractants have been developed for M. signata, highlighting the practical potential of the plant volatile mixtures identified in this study. In addition, replicated field experiments across different climatic regions are essential to validate the consistency and applicability of attractant formulations in diverse environmental settings. Despite these challenges, plant-derived synthetic attractants remain promising tools for monitoring and managing leaf beetle populations as they can attract both sexes and contribute to integrated pest management programs [20].
Three types of attractant formulations were selected in this study based on the volatile compounds emitted from cotton and corn leaves. These compounds, including leaf alcohol, β-pinene, trans-2-hexen-1-al, α-phellandrene, trans-2-hexen-1-ol, and 1-heptene are common green leaf volatiles widely found in plants and play important roles in mediating interactions between host plants and phytophagous insects [55]. Leaf alcohol has been reported to enhance courtship behavior in certain Lepidoptera and Coleoptera species [56,57,58], and also shows moderate attractiveness to Anoplophora glabripennis [59]. β-pinene, as the main component in attractants, significantly attracts Monochamus alternatus [60]. Attractants containing trans-2-hexen-1-al strongly attract Asias halodendri [61,62], while α-phellandrene-based attractants are effective against Ips pini in the field [63]. Trans-2-hexen-1-ol attracts Chlorophorus diadema and Curculio chinensis [64,65], and 1-heptene elicits strong EAG responses in A. glabripennis [66]. The volatile components identified in this study are consistent with those reported previously and likely represent the key constituents responsible for attracting M. signata.
Although this study identified several plant-derived volatile mixtures with strong laboratory and field attractiveness (mixtures 22, 23, and 26), we acknowledge several limitations that should be addressed in future research. First, the actual release dynamics of volatile blends from polyethylene slow-release dispensers were not quantitatively monitored. Techniques such as dynamic headspace sampling and GC–MS analysis would allow characterization of the types, ratios, and release rates of volatiles under both laboratory and field conditions, helping verify whether the “odor profile” tested in the laboratory corresponds to that emitted in the field. Second, environmental factors such as crop growth stage, surrounding vegetation, and background odors may influence lure performance and partially explain the discrepancies between laboratory and field results. Incorporating these factors in future field trials will help improve the robustness and practical reliability of these attractant formulations. Overall, our findings provide a basis for the development and application of plant-based attractants for M. signata and may contribute to environmentally friendly pest management strategies, including biological control.

5. Conclusions

In this study, we identified and evaluated plant-derived volatile mixtures that elicited strong electrophysiological and behavioral responses in Monolepta signata. Among them, the mixture 23 (α-phellandrene + trans-2-hexen-1-ol + 1-heptene) was consistently attractive to M. signata and showed superior field trapping performance. Based on these findings, mixture 23 was granted a Chinese invention patent for its use as an attractant formulation for M. signata (Patent No. ZL202110177367.0). This formulation can be integrated into slow-release polyethylene lures and used in field-monitoring traps to facilitate the early detection and control of M. signata infestations. Future research should optimize dispenser design, assess long-term stability, and evaluate its compatibility with integrated pest management (IPM) strategies in different cropping systems.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/insects16121233/s1.

Author Contributions

Conceptualization: L.L. and J.C. (Jing Chen) designed the research framework and formulated the experimental plan; investigation and data curation: L.L., Z.C. and J.C. (Jiyu Cao) carried out the experiments, collected data, and curated the datasets to ensure data integrity and accuracy; writing—original draft: L.L. and J.C. (Jiyu Cao) drafted the initial manuscript; funding acquisition: J.C. (Jing Chen) jointly secured the research funding; supervision—review and editing: both Z.C. and J.C. (Jing Chen) reviewed, revised, and finalized the manuscript, and also supervised the overall research progress while ensuring the accuracy of the experimental results. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Xinjiang Production and Construction Corps Guiding Science and Technology Plan Project (2022ZD010), the National Natural Science Funds of China (No. 31960541 and NO. 31460473), Xinjiang Uygur Autonomous Region Key Science and Technology Task Special (2023A02009), Project of Fund for Stable Support to Agricultural Sci-Tech Renovation (xjnkywdzc-2025002-13), and These funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding authors.

Acknowledgments

Thank you to Jianping Zhang and Jie Su for their guidance in experimental design and methods. Thank you to Chen Yang and Dandan Guo from Shihezi University for their help in the experiment. We are grateful to the reviewer and the editor for comments and suggestions.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
EAGElectroantennogram
SE Standard error

References

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Insects 16 01233 g001
Figure 1. Electroantennogram (EAG) response of female M. signata to 26 mixtures of plant volatiles. These data represent the mean ± SE, while the by letters indicate the results of mixed volatiles on the different types by Duncan’s multiple range test. * indicates a significant difference (p < 0.05, independent-samples t-test) between female and male antennae in response to the same volatile compound.
Figure 1. Electroantennogram (EAG) response of female M. signata to 26 mixtures of plant volatiles. These data represent the mean ± SE, while the by letters indicate the results of mixed volatiles on the different types by Duncan’s multiple range test. * indicates a significant difference (p < 0.05, independent-samples t-test) between female and male antennae in response to the same volatile compound.
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Insects 16 01233 g002
Figure 2. Electroantennogram (EAG) response of male M. signata to 26 plant volatile mixtures. These data represent the mean ± SE, while the letters indicate the results of mixed volatile on the different types by Duncan’s multiple range test. * indicates a significant difference (p < 0.05, independent-samples t-test) between female and male antennae in response to the same volatile compound.
Figure 2. Electroantennogram (EAG) response of male M. signata to 26 plant volatile mixtures. These data represent the mean ± SE, while the letters indicate the results of mixed volatile on the different types by Duncan’s multiple range test. * indicates a significant difference (p < 0.05, independent-samples t-test) between female and male antennae in response to the same volatile compound.
Insects 16 01233 g002
Insects 16 01233 g003
Figure 3. Behavior response of M. signata of female adults to eight plant volatile mixtures. The data obtained were all tested by χ2, * indicates significant difference (p < 0.05), and ns indicates no choice.
Figure 3. Behavior response of M. signata of female adults to eight plant volatile mixtures. The data obtained were all tested by χ2, * indicates significant difference (p < 0.05), and ns indicates no choice.
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Insects 16 01233 g004
Figure 4. Behavior response of M. signata of male adults to eight mixtures of plant volatiles. The data obtained were all tested by χ2, * indicates significant difference (p < 0.05), and ns indicates no choice.
Figure 4. Behavior response of M. signata of male adults to eight mixtures of plant volatiles. The data obtained were all tested by χ2, * indicates significant difference (p < 0.05), and ns indicates no choice.
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Insects 16 01233 g005
Figure 5. Field trapping effect of six different mixtures of plant volatiles on the M. signata adults. Data are presented as the means ± SEMs. Different lowercase indicates significant difference at the p < 0.05 level.
Figure 5. Field trapping effect of six different mixtures of plant volatiles on the M. signata adults. Data are presented as the means ± SEMs. Different lowercase indicates significant difference at the p < 0.05 level.
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Table 1. The standard chemical samples in the experiment.
Table 1. The standard chemical samples in the experiment.
CompoundsCAS NumberPurity (%)Producer
β-ocimene3779-61-198Toronto Research Chemicals
(Vaughan, ON, Canada)
1-heptene592-76-798Bejing Ouhe Technology Co., Ltd.
(Beijing, China)
aromadendrene489-39-497Sigma-Aldrich
(St. Louis, MO, USA)
trans-2-hexen-1-al6728-26-398Bejing Ouhe Technology Co., Ltd.
α-farnesene502-61-498Toronto Research Chemicals
heptadecane629-78-798Bejing Ouhe Technology Co., Ltd.
trans-2-hexen-1-ol928-95-098Bejing Ouhe Technology Co., Ltd.
(Z)-3-hexen-1-ol (Leaf alcohol)928-96-198Bejing Ouhe Technology Co., Ltd.
α-phellandrene99-83-298Bejing Ouhe Technology Co., Ltd.
β-pinene127-91-398Bejing Ouhe Technology Co., Ltd.
α-caryophyllene6753-98-698Bejing Ouhe Technology Co., Ltd.
hexadecene629-73-298Bejing Ouhe Technology Co., Ltd.
nerolidol7212-44-498Bejing Ouhe Technology Co., Ltd.
3-methylpentanal15877-57-398Toronto Research Chemicals
n-hexane110-54-397Tianjin Fuyu Fine Chemical Co., Ltd.
(Tianjin, China)
paraffin liquid8042-47-599Tianjin Yongcheng Fine Chemical Co., Ltd.
(Tianjin, China)
Note: The compounds 1-heptene, aromadendrene, trans-2-hexen-1-ol, α-phellandrene, α-caryophyllene, and hexadecene in the table are from cotton leaves; the compounds α-farnesene and heptadecane are from corn leaves; and the compounds β-ocimene, trans-2-hexenal-1-al, leaf alcohol, β-pinene, nerolidol, and 3-methylpentanal are from both cotton leaves and corn leaves.
Table 2. Compositions and contents of twenty-six mixtures of plant volatiles.
Table 2. Compositions and contents of twenty-six mixtures of plant volatiles.
MixtureCompositionConcentration (μL/mL)
1β-pinene + leaf alcohol10 + 10
2β-pinene + trans-2-hexen-1-al10 + 10
3β-pinene + aromadendrene10 + 10
4α-phellandrene + trans-2-hexen-1-ol10 + 10
5α-phellandrene + trans-2-hexen-1-al10 + 10
6α-phellandrene + leaf alcohol10 + 10
7α-phellandrene + α-farnesene10 + 1
8trans-2-hexen-1-al + leaf alcohol10 + 10
9trans-2-hexen-1-al + trans-2-hexen-1-ol10 + 10
10trans-2-hexen-1-al + aromadendrene10 + 10
11leaf alcohol + 1-heptene10 + 10
12leaf alcohol + α-farnesene10 + 1
13trans-2-hexen-1-ol + 1-heptene10 + 10
14trans-2-hexen-1-ol + nerolidol10 + 10
151-heptene + nerolidol10 + 10
161-heptene + α-farnesene10 + 1
17nerolidol + aromadendrene10 + 10
18aromadendrene + α-farnesene10 + 1
19β-pinene + α-phellandrene + trans-2-hexen-1-al10 + 10 + 10
20leaf alcohol + trans-2-hexen-1-ol +1-heptene10 + 10 + 10
21nerolidol + aromadendrene + α-farnesene10 + 10 + 1
22β-pinene + trans-2-hexen-1-al +leaf alcohol10 + 10 + 10
23α-phellandrene + trans-2-hexen-1-ol + 1-heptene10 + 10 + 10
24leaf alcohol + nerolidol + aromadendrene10 + 10 + 10
25trans-2-hexen-1-ol + nerolidol + aromadendrene10 + 10 + 10
26trans-2-hexen-1-al + 1-heptene + trans-2-hexen-1-ol10 + 10 + 10
Table 3. Results for the chi-square tests regarding the effects of female and male of the M. signata adults to different combinations in the Y-tube olfactometer assays.
Table 3. Results for the chi-square tests regarding the effects of female and male of the M. signata adults to different combinations in the Y-tube olfactometer assays.
CombinationsGenderχ2dfpp (Bonferroni Corrected)
Mixture 1 vs. CKFemale3.98110.0460.067
Mixture 4 vs. CKFemale0.90810.3410.430
Mixture 12 vs. CKFemale1.33310.2480.320
Mixture 20 vs. CKFemale5.05510.0250.037
Mixture 22 vs. CKFemale1.17110.2790.357
Mixture 23 vs. CKFemale5.76210.0160.025
Mixture 25 vs. CKFemale1.12610.2890.368
Mixture 26 vs. CKFemale6.24810.0120.020
Mixture 4 vs. CKMale1.12610.2890.368
Mixture 8 vs. CKMale0.25310.6150.733
Mixture 19 vs. CKMale4.24410.0390.058
Mixture 20 vs. CKMale0.80510.3700.461
Mixture 22 vs. CKMale6.06110.0140.021
Mixture 23 vs. CKMale4.14410.0420.061
Mixture 24 vs. CKMale0.18710.6660.857
Mixture 26 vs. CKMale2.52210.1120.154
Table 4. The average number of M. signata adults every two days.
Table 4. The average number of M. signata adults every two days.
TreatmentDate
14 July16 July18 July20 July22 July24 July26 July
Mixture 11.7 ± 1.2 a2.7 ± 0.3 ab1.0 ±1.0 ab2.3 ± 0.3 a0.7 ± 0.7 a1.3 ± 0.9 ab1.0 ± 0.6 a
Mixture 192.0 ± 1.5 a3.7 ± 1.3 ab1.0 ± 0.0 ab3.3 ± 2.3 a0.7 ± 0.3 a0.7 ± 0.7 b0.3 ± 0.3 a
Mixture 201.7 ± 1.2 a2.7 ± 0.9 ab3.3 ± 1.7 a1.3 ± 0.3 a0.3 ± 0.3 a2.0 ± 0.6 ab1.3 ± 0.9 a
Mixture 221.7 ± 0.3 a5.0 ± 1.2 a1.3 ± 0.3 ab2.0 ± 0.6 a1.0 ± 0.6 a1.7 ± 0.7 ab1.0 ± 0.6 a
Mixture 234.0 ± 1.5 a4.3 ± 1.2 a2.3 ± 0.9 ab2.3 ± 0.7 a1.0 ± 0.6 a3.3 ± 0.9 a0.3 ± 0.3 a
Mixture 262.7 ± 0.7 a3.3 ± 0.7 ab3.0 ± 0.6 a2.0 ± 1.5 a1.3 ± 0.3 a1.0 ± 1.0 ab0.7 ± 0.7 a
CK0.7 ± 0.3 a1.0 ± 0.0 b0.0 ± 0.0 b0.7 ± 0.3 a0.3 ± 0.3 a0.7 ± 0.3 b0.3 ± 0.3 a
Note: Data are presented as the mean ± SE. Different lowercase indicates a signifcant difference at the p < 0.05 level.
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Li, L.; Cao, J.; Cai, Z.; Chen, J. Plant Volatile Organic Compounds Attractive to Monolepta signata (Olivier). Insects 2025, 16, 1233. https://doi.org/10.3390/insects16121233

AMA Style

Li L, Cao J, Cai Z, Chen J. Plant Volatile Organic Compounds Attractive to Monolepta signata (Olivier). Insects. 2025; 16(12):1233. https://doi.org/10.3390/insects16121233

Chicago/Turabian Style

Li, Lun, Jiyu Cao, Zhiping Cai, and Jing Chen. 2025. "Plant Volatile Organic Compounds Attractive to Monolepta signata (Olivier)" Insects 16, no. 12: 1233. https://doi.org/10.3390/insects16121233

APA Style

Li, L., Cao, J., Cai, Z., & Chen, J. (2025). Plant Volatile Organic Compounds Attractive to Monolepta signata (Olivier). Insects, 16(12), 1233. https://doi.org/10.3390/insects16121233

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