Identification and evaluation of cruciferous plant volatiles attractive to Plutella xylostella L. (Lepidoptera: Plutellidae).

BACKGROUND: The diamondback moth, Plutella xylostella, has developed resistance to almost all insecticides used for its control. The 'push-pull' method has been shown as an effective control strategy to address this resistance challenge of P. xylostella. The key focus of the strategy is the identification of attractive or repellent volatile components. The aim of this study was to identify attractive volatile compounds released from host plants. Identified compounds were applied in the biological control of this pest. RESULTS: Nine active compounds released into the headspace of seven cruciferous plant species were identified using gas chromatography-electroantennographic detection and gas chromatography-mass spectrometry. Electroantennographic detection-active compounds included five green leaf volatiles (hexanal, trans-2-hexen-1-ol, cis-3-hexen-1-ol, cis-3-hexenyl acetate, and 1-penten-3-ol), three isothiocyanates (isopropyl isothiocyanate, allyl isothiocyanate, and butyl isothiocyanate), and nonanal. Except for nonanal, all the identified green leaf volatiles and isothiocyanates elicited strong electrophysiological and behavioral responses in P. xylostella. The strongest attractive compounds, trans-2-hexen-1-ol and isopropyl isothiocyanate, were further evaluated in oviposition and field-trapping assays. Results showed that they both lured female moths to lay eggs, and were highly attractive to P. xylostella adults in field, especially when used in combination with yellow and green sticky boards. However, a blend of the two compounds showed no synergistic effect, but rather an antagonistic effect. CONCLUSIONS: Green leaf volatiles and isothiocyanates were identified as key olfactory cues for host selection of P. xylostella. Trans-2- hexen-1-ol and isopropyl isothiocyanate were identified as candidate attractive compounds to serve in a 'push-pull' strategy for P. xylostella control. © 2023 Society of Chemical Industry.

Aphid-repellent, ladybug-attraction activities, and binding mechanism of methyl salicylate derivatives containing geraniol moiety.

BACKGROUND: Aphids have been mainly controlled by traditional chemical insecticides, resulting in unamiable risk to the environment over the last decades. Push-pull strategy is regarded as a promising eco-friendly approach for aphid management through repelling aphid away and attracting their natural enemy. Methyl salicylate (MeSA), one of typical HIPVs (herbivore-induced plant volatiles), can repel aphids and attract ladybugs. Our previous studies discovered a new lead compound 3e, a salicylate-substituted carboxyl (E)-ß-farnesene derivative that had effective aphid-repellent activity. However, whether 3e has attractive activity to ladybug like MeSA is unknown. Meanwhile, to discover a new derivative for both deterring aphid and recruiting ladybug is meaningful for green control of aphids. RESULTS: Through the structural optimization of 3e, 14 new derivatives were designed and synthesized. Among them, compounds 4e and 4i had good aphid (Acyrthosiphon pisum) repellent activity, and compounds 3e, 4e and 4i had significant ladybug (Harmonia axyridis) attractive activity to males. Particularly, 4i exhibited manifest attractive effect on the females as well. Binding mechanism showed that 4i not only bound effectively with the aphid (Acyrthosiphon pisum) target ApisOBP9 thanks to its multiple hydrophobic interactions and hydrogen-bond, but also had strong binding affinity with ladybug target HaxyOBP15 due to the suitable steric space. Additionally, 4i displayed low toxicity to bee Apis mellifera. CONCLUSION: Compound 3e does exhibit attractive activity to male ladybug as MeSA. However, the new derivative 4i, with both pleasant aphid-repellent and ladybug-attraction activities, can be considered as a novel potential push-pull candidate for aphid control in sustainable agriculture. © 2022 Society of Chemical Industry.

Behavioral Responses of Bemisia tabaci Mediterranean Cryptic Species to Three Host Plants and Their Volatiles.

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a worldwide pest that damages over 900 host plant species. The volatile organic compounds (volatiles) of contrasting plants, as well as their growth stage, influence this pest's infestation behavior. The chemical contents of volatiles isolated from three plants (Gossypium hirsutum, Abutilon theophrasti, and Ricinus communis) during various growth phases (pre-flowering, fluorescence, and fruiting) were examined, as well as their influence on the behavior of adult B. tabaci. The olfactometer studies demonstrated that growth periods of the three plants affected the preference of B. tabaci. Volatiles of piemarker and cotton plants had dissimilar levels of attraction to adults during all stages. Volatile substances released by the castor at the stage of flowering had repellent effect on B. tabaci. In the plant versus plant combination, piemarker volatiles before and during anthesis were most preferred by adults, followed by cotton and then castor. A total of 24, 24, and 20 compounds were detected from volatiles of piemarker, cotton, and castor, respectively, and proportions among the compounds changed during different stages of plant development. The olfactory responses of B. tabaci to volatile compounds presented that linalool and high concentration of (Z)-3-hexenyl acetate had a strong trapping effect on this pest, while nonanal had a significant repellent effect at high concentration. This study indicates that distinct plants and their growth stage affect their attractiveness or repellency to B.tabaci adults, which are mediated by changing plant volatiles. These compounds obtained by analysis screening can be adopted as potential attractants or repellents to control Mediterranean (MED) B. tabaci.

Association between olfactory sensitivity and behavioral responses of Drosophila suzukii to naturally occurring volatile compounds.

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive, destructive crop pest that originated in South East Asia. D. suzukii recently invaded Western countries and is threatening both European and American fruit industries. It is extremely attracted to otherwise undamaged, ripening fruits, unlike most other Drosophila species that attack only decaying or rotten fruits. Recent studies on different insect species showed that several naturally occurring compounds of easy market availability showing deterrent action may be used to supplement mass catches with food traps. Based on these considerations, the aim of the present work was to test the effects of some natural compounds (alone or in the mixture) on the olfactory system of the D. suzukii and the behavioral responses evoked. We measured by electroantennogram (EAG) recordings, the olfactory sensitivity of antennae to increasing concentrations of eugenol, vanillin, menthol, cis-jasmone; eugenol + vanillin, +menthol, +cis-jasmone; vanillin + menthol, +cis-jasmone. In addition, the behavioral responses to the same compounds and mixtures were evaluated. Our electrophysiological results show a dose-response relationship between the EAG amplitudes and the increasing concentrations of the olfactory compound. The behavioral results show that the number of laid eggs is significantly different between the standard diet and the standard diet + natural compound. These results underline a specificity in the olfactory sensitivity and in the ovipositing behavior of D. suzukii females; also, they could be valuable for the identification of key chemicals aimed at the future development of strategies in the management and control of this harmful insect for crops.

Behavioral and Electrophysiological Effects of Ajowan (Trachyspermum ammi Sprague) (Apiales: Apiaceae) Essential Oil and Its Constituents on Nymphal and Adult Bean Bugs, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae).

We investigated the repellent effect of 12 Apiaceae plant essential oils on nymphal and adult (male and female) forms of the bean bug, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae), using a four-arm olfactometer. Among the essential oils tested, ajowan (Trachyspermum ammi Sprague) essential oil showed the strongest repellent activity against the nymphal and adult bean bugs. For female adults, the repellent activity was significantly different between an ajowan oil-treated chamber and an untreated chamber down to a concentration of 14.15 µg/cm2. We also investigated the repellent activity of individual ajowan essential oil constituents. Of the compounds examined, carvacrol and thymol showed the most potent repellent activity against the nymphal and adult bean bugs. Carvacrol and thymol exhibited 73.08% and 70.0% repellent activity for the bean bug nymph at 0.71 and 2.83 µg/cm2, respectively, and 82.6% and 80.7% at 5.66 and 11.32 µg/cm2, respectively, for male adults. Carvacrol and thymol exhibited strong repellent activity against female adult bean bugs down to a concentration of 2.83 µg/cm2. Ajowan essential oil, thymol and carvacrol elicited a negative electroantennogram (EAG) response from adult bean bugs. This could explain the repellent activity of ajowan essential oil and its constituents. Our results indicate that ajowan essential oil and its constituents carvacrol and thymol can be potential candidates as the 'push' component in a 'push-pull' strategy for bean bug control.

Characterizing potential repelling volatiles for "push-pull" strategy against stem borer: a case study in Chilo auricilius.

BACKGROUND: Massive techniques have been evaluated for developing different pest control methods to minimize fertilizer and pesticide inputs. As "push-pull" strategy utilizes generally non-toxic chemicals to manipulate behaviors of insects, such strategy is considered to be environmentally friendly. "Push-pull" strategy has been extraordinarily effective in controlling stem borers, and the identification of new "pushing" or "pull" components against stem borers could be significantly helpful. RESULTS: In this study, the results of field trapping assay and behavioral assay showed the larvae of C.auricilius, one kind of stem borers, could be deterred by rice plant under tilling stage, its main host crop. The profiles of volatiles were compared between rice plants under two different developmental stages, and α-pinene was identified as a key differential component. The repelling activity of α-pinene against C.auricilius was confirmed by Y-tube olfactometer. For illuminating the olfactory recognition mechanism, transcriptome analysis was carried out, and 13 chemosensory proteins (CSPs) were identified in larvae and 19 CSPs were identified in adult of C.auriciliu, which was reported for the first time in this insect. Among these identified CSPs, 4 CSPs were significantly regulated by α-pinene treatment, and CSP8 showed good binding affinity with α-pinene in vitro. CONCLUSIONS: Overall, C.auricilius could be repelled by rice plant at tilling stage, and our results highlighted α-pinene as a key component in inducing repelling activity at this specific stage and confirmed the roles of some candidate chemosensory elements in this chemo-sensing process. The results in this study could provide valuable information for chemosensory mechanism of C.auricilius and for identification of "push" agent against rice stem borers.

Influence of Location and Distance of Biogents Sentinel™ Traps From Human-Occupied Experimental Huts On Aedes aegypti Recapture and Entry Into Huts.

A mark-release-recapture study was conducted to refine the "push-pull" strategy for controlling the dengue, chikungunya, and Zika virus vector Aedes aegypti in a peridomestic environment by determining optimal locations and distances from human-occupied experimental huts for placement of the "pull" component (Biogents Sentinel™ [BGS] traps) to maximize the capture of mosquitoes. The BGS traps were placed at portals of entry (windows or doors) or corners of the experimental huts and at varying distances from the huts (0, 3, and 10 m). The location optimization trials revealed higher trap capture rates and reduction in entry of mosquitoes when the BGS traps were positioned nearer the experimental hut portals of entry than those placed in the corner of the huts. The trap capture rate at huts' portals of entry was 38.7% (116/300), while the corners recorded 23.7% (71/300). The percentage reduction in entry of mosquitoes into the huts was 69% and 31% at portals of entry and corners or vertices, respectively. In the distance optimization trials, the highest captures were recorded at 0 m (18.5%; 111/600) and 10 m (14.2%; 128/900) distances from the hut. Moreover, the highest percentage reduction in entry of mosquitoes into the huts occurred for traps set at 0 m (65.6%) compared with 3 m (17.2%) or 10 m (14.6%) distances from the huts.

BG-Sentinel™ Trap Efficacy As A Component of Proof-Of-Concept For Push-Pull Control Strategy For Dengue Vector Mosquitoes.

The efficacy of the BG-Sentinel™ (BGS) trap as a "pull" component of a "push-pull" system (PPS) for management of the dengue vector, Aedes aegypti, was evaluated using local households in Pu Tuey, Kanchanaburi, Thailand. The pull component was the concluding phase of a 3-part investigation using a PPS combination spatial repellent (SR) and BGS trap to capture adult vector mosquitoes. Two sentinel households were selected for evaluation of BGS trap efficacy based on the highest pretrial indoor resting densities of Ae. aegypti using Centers for Disease Control and Prevention (CDC) mechanical backpack collections. Potential Ae. aegypti resting sites around the selected houses were identified as possible competing sites that might influence the BGS trap capture efficiency. Results showed that BGS traps were productive in capturing Ae. aegypti females (93.4% of all Aedes collected) in the presence of competing man-made, artificial resting sites. The CDC backpack aspirator collections provided an indirect measure of local Aedes population, although technically not comparable for supporting productivity of BGS traps due to different collection days and households sampled. The predominant competing resting sites were water containers found within 3 m around the outside of sentinel households. The most productive BGS collections between houses differed by location. The most productive period of operation for Ae. aegypti BGS trapping was between 1330 and 1730 h. The BGS trap appears an effective "pull" device in the PPS strategy in natural settings.

The push-pull strategy for citrus psyllid control.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the only natural vector of Candidatus Liberibacter asiaticus that causes citrus huanglongbing (HLB), a most destructive disease of citrus. Currently, no remedial therapy exists for the disease, and so effective control of ACP is very important in curbing the transmission of the disease. The push-pull strategy should be thoroughly explored as an approach to ACP management. This mini-review summarises the current progress towards more effective repellent and attractant chemicals through investigating known repellent and attractive plants. Interactions between ACP and its host plants are also addressed, with emphasis on the possible involvement of the host biochemicals in attracting the insect. Potential ways to increase the effectiveness of the pull-push strategy are briefly discussed. It is expected that the pull-push strategy will be gradually developed following more extensive research.

Electrophysiological and behavioural responses of the tea geometrid Ectropis obliqua (Lepidoptera: Geometridae) to volatiles from a non-host plant, rosemary, Rosmarinus officinalis (Lamiaceae).

BACKGROUND: A plant-based 'push-pull' strategy for Ectropis obliqua (Prout) (Lepidoptera: Geometridae) is being developed using semiochemicals in the volatiles of Rosmarinus officinalis (Lamiaceae). The aim of this study was to identify and quantify the bioactive components within R. officinalis by gas chromatography-electroantennographic detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS), and to test the antennal and behavioural responses of E. obliqua to these chemicals. The emission dynamics of bioactive chemicals was also monitored. RESULTS: GC-EAD experiments indicated that E. obliqua antennae responded to the following volatile compounds from R. officinalis: myrcene, α-terpinene, γ-terpinene, linalool, cis-verbenol, camphor, α-terpineol and verbenone, which were the minor constituents. Based on the dose-dependent antennal and behavioural responses of E. obliqua to these bioactive compounds, myrcene, γ-terpinene, linalool, cis-verbenol, camphor and verbenone were found to play a key role in repelling the moths, and the mixture that included all eight compounds was significantly more effective. The maximum emissions of these semiochemicals occurred at nightfall. CONCLUSIONS: The specifically bioactive compounds in R. officinalis volatiles are responsible for repelling E. obliqua adults. Results indicate that R. officinalis should be considered as a potential behaviour-modifying stimulus for 'push' components when developing 'push-pull' strategies for control of E. obliqua using semiochemicals.

A comparison of two commercial mosquito traps for the capture of malaria vectors in northern belize, central america.

To achieve maximum success from any vector control intervention, it is critical to identify the most efficacious tools available. The principal aim of this study was to evaluate the efficacy of 2 commercially available adult mosquito traps for capturing Anopheles albimanus and An. vestitipennis, 2 important malaria vectors in northern Belize, Central America. Additionally, the impact of outdoor baited traps on mosquito entry into experimental huts was assessed. When operated outside of human-occupied experimental huts, the Centers for Disease Control and Prevention (CDC) miniature light trap, baited with human foot odors, captured significantly greater numbers of female An. albimanus per night (5.1 ± 1.9) than the Biogents Sentinel™ trap baited with BG-Lure™ (1.0 ± 0.2). The 2 trap types captured equivalent numbers of female An. vestitipennis per night, 134.3 ± 45.6 in the CDC trap and 129.6 ± 25.4 in the Sentinel trap. When compared to a matched control hut using no intervention, the use of baited CDC light traps outside an experimental hut did not impact the entry of An. vestitipennis into window interception traps, 17.1 ± 1.3 females per hour in experimental huts vs. 17.2 ± 1.4 females per hour in control huts. However, the use of outdoor baited CDC traps did significantly decrease the entry of An. albimanus into window interception traps from 3.5 ± 0.5 females per hour to 1.9 ± 0.2 females per hour. These results support existing knowledge that the underlying ecological and behavioral tendencies of different Anopheles species can influence trap efficacy. Furthermore, these findings will be used to guide trap selection for future push-pull experiments to be conducted at the study site.

A comparison of two commercial mosquito traps for the capture of Malaria vectors in northern Belize, Central America

To achieve maximum success from any vector control intervention, it is critical to identify the most efficacious tools available. The principal aim of this study was to evaluate the efficacy of 2 commercially available adult mosquito traps for capturing Anopheles albimanus and An. vestitipennis, 2 important malaria vectors in northern Belize, Central America. Additionally, the impact of outdoor baited traps on mosquito entry into experimental huts was assessed. When operated outside of human-occupied experimental huts, the Centers for Disease Control and Prevention (CDC) miniature light trap, baited with human foot odors, captured significantly greater numbers of female An. albimanus per night (5.1 6 1.9) than the Biogents SentinelTM trap baited with BG-LureTM (1.0 6 0.2). The 2 trap types captured equivalent numbers of female An. vestitipennis per night, 134.3 6 45.6 in the CDC trap and 129.6 6 25.4 in the Sentinel trap. When compared to a matched control hut using no intervention, the use of baited CDC light traps outside an experimental hut did not impact the entry of An. vestitipennis into window interception traps, 17.1 6 1.3 females per hour in experimental huts vs. 17.2 6 1.4 females per hour in control huts. However, the use of outdoor baited CDC traps did significantly decrease the entry of An. albimanus into window interception traps from 3.5 6 0.5 females per hour to 1.9 6 0.2 females per hour. These results support existing knowledge that the underlying ecological and behavioral tendencies of different Anopheles species can influence trap efficacy. Furthermore, these findings will be used to guide trap selection for future push­ pull experiments to be conducted at the study site...(AU)