Herbivore-induced plant volatiles emitted by citrus in response to spider mite infestation can attract predatory mites

Understanding the nutritional interplay among plants, pests, and natural enemies is essential for sustainable pest management. Enhancing the efficiency of natural enemies, such as Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is critical, and exploiting herbivore-induced plant volatiles (HIPVs) offers a promising approach. However, N. californicus has rarely been reported to utilize HIPVs to improve their biological control capabilities. Our research revealed a significant difference in the diversity of volatile compounds detected in clean Citrus reticulata Blanco leaves compared to those in C. reticulata leaves infested with Panonychus citri (McGregor) (Acari: Tetranychidae), regardless of mite presence. This suggests that P. citri infestation induces a wide array of HIPVs in C. reticulata leaves. We conducted olfactory behavioral assays to evaluate the response of N. californicus to synthetic HIPVs. Results revealed that linalool (1.00 mg/mL), 2,2,4-trimethylpentane (10.0 mg/mL), undecylcyclohexane (1.00 mg/mL), and (+)-dibenzoyl-L-tartaric anhydride (10.0 mg/mL) significantly attracted N. californicus while pentadecanal (1.00 mg/mL) significantly deterred it. A 3-component blend of linalool, undecylcyclohexane, and (+)-dibenzoyl-L-tartaric anhydride was better than other combinations in attracting N. californicus. This combination provided the basis for developing an attractant for N. californicus, facilitating the rate of its dispersal to enhance its biological control of pests. Consequently, this research offers vital insights into improving the sustainable pest control potential of predatory mites.

Assessment of Attractant Combinations for the Management of Red Palm Weevils (Rhynchophorus ferrugineus) in the United Arab Emirates

This study examined red palm weevil ecology in the United Arab Emirates to develop effective food baits, pheromone, and eco-friendly trapping methods. Three phases of investigation were conducted (from June to December 2023) on date palm farms in Ras Al Khaimah and Abu Dhabi. The first two phases, each 15 days long, were conducted in Ras Al Khaimah, whereas the third phase, 18 days long, was conducted in Abu Dhabi. Chemical attractants, such as existing pheromones and ethyl acetate, a newly synthesized ferruginol pheromone, and food baits, such as original dates, date paste, coconut water, and date palm syrup, were used to attract the weevils. Multi-funnel traps containing various attractant mixes were tested. The main activity of the red palm weevils was observed from 3:00 to 6:00 a.m., with 85.72 ± 3.39% being captured during this period, coinciding with cooler temperatures. When pheromones were added to the food bait, the capture rate increased by 6.95 ± 1.81 times. Combining food bait, ethyl acetate, and pheromones improved the capture rates by 3.14 ± 0.69 times compared to pheromones alone. The newly synthesized pheromone achieved capture rates 2.69 ± 0.07 times higher than those of the commercially available pheromone, confirming its suitability as a red palm weevil attractant.

Grass Infusions in Autocidal Gravid Ovitraps to Lure Aedes Albopictus

Aedes albopictus is a vector of several pathogens of significant public health concern. In this situation, gravid traps have become a common surveillance tool for Aedes spp., which commonly use hay infusions as an attractant. Diverse grass infusions have been assessed to enhance the attraction to this vector mosquito. However, these studies have focused on the oviposition effect, and the attraction potential to gravid Ae. albopictus females has not been evaluated yet. Here we report the attractiveness of infusions of 4 different botanical species (Cenchrus purpureus, Cyanodon dactylon, Megathyrus maximus, Pennisetum ciliare) as baits in sticky ovitraps and autocidal gravid ovitraps (AGOs) under laboratory, semifield, and field conditions. In the laboratory, Cynodon dactylon showed attractiveness, whereas in semifield conditions, both C. dactylon and Megathyrsus maximus were similarly attractive for gravid Ae. albopictus. None of the infusions conducted with AGOs were able to lure Ae. albopictus and other species of mosquitoes in a 14-wk field experiment. Our results demonstrate the feasibility of finding more attractive infusions for Ae. albopictus females to improve the efficacy of AGO traps, but further testing of infusions in AGOs in field settings is needed.

Dancing in the purple rain: color affinity and oviposition choices in Aedes sierrensis (Diptera: Culicidae)

The western tree hole mosquito, Aedes sierrensis (Ludlow) (Diptera: Clucidae), is a pestiferous mosquito with a range extending over the entire pacific seaboard and into portions of the intermountain west. As a peridomestic heartworm vector, it demands at least some level of surveillance to understand its abundance. However, the species is refractory to a majority of conventional vector surveillance approaches for tracking mosquitoes. To find more options for Aedes sierrensis surveillance, a variety of oviposition attractants were evaluated in arena-style choice assays using colony reared adults. A range of infusion treatments (e.g., alfalfa, oak, and beetroot) were examined and then combined with investigations of liquid color as well as ovicup color and entryway position. These studies revealed that Ae. sierrensis have an affinity for purple coloration, plain water, and larger entryway sizes for oviposition cups. A prototype ovicup was 3D-printed using purple filament and multiple types of entryways, and used to re-test infusion waters. No particular attraction differences were detected after normalizing for purple color. Comparisons to black 3D-printed cups yielded surprising observations that male mosquitoes also aggregated on purple cups while females sheltered, but not necessarily oviposited, in black cups. Although this was only a laboratory-based assessment, these studies provide useful information for future field trials of potential oviposition traps for surveillance of Ae. sierrensis.

Identification of floral volatiles from Fagopyrum esculentum that attract Cotesia vestalis with potentially better biocontrol efficacy against Plutella xylostella

BACKGROUND

Nectar plants provide extra nourishment for parasitoids, which can utilize floral volatiles to locate nectar-rich flowers. A promising strategy is to screen potential floral species based on the wasps' olfactory preferences for nectar sources, and to ensure their suitability for both natural enemies and targeted pests. Cotesia vestalis (Haliday) is a dominant parasitoid of the oligophagous pest Plutella xylostella, which poses a significant threat to cruciferous vegetables globally. However, the chemical cues in plant-parasitoid complexes mediating Cotesia vestalis to locate nectar food resources and the positive effect of nectar plants on the Cotesia vestalis population are poorly understood.

RESULTS

The results showed that Fagopyrum esculentum was the most attractive plant that attracted Cotesia vestalis, not Plutella xylostella in 44 flowering plants from 19 families. 1,2-Diethyl benzene and 1,4-diethyl benzene, identified from the floral volatiles from F. esculentum in full bloom, were found to elicit dose-dependent electrophysiological responses and attract Cotesia vestalis adults, demonstrating their potential as semiochemicals. Moreover, the age-stage, two-sex life table revealed that feeding on nectar food increased the efficacy of Cotesia vestalis adults against Plutella xylostella.

CONCLUSION

In summary, the findings provide insights into the chemical ecology of plant-parasitoid complexes and support the potential use of F. esculentum as insectary plants in habitat manipulation against Plutella xylostella by supplying natural nectar food for the Cotesia vestalis population. Our results suggest an attract and reward strategy based on an attractant for Cotesia vestalis to control Plutella xylostella, or the development of volatile-based artificial food for Cotesia vestalis. © 2023 Society of Chemical Industry.

Booklice Liposcelis bostrychophila are efficiently attracted by the combination of 2,3,5,6-tetramethylpyrazine and ultraviolet light

BACKGROUND

Booklice Liposcelis bostrychophila are frequently found almost everywhere, including private houses and cleanrooms of factories and institutes. They often cause serious hygienic as well as agricultural problems, but a useful trap has not been developed so far. Therefore, an effective way to monitor and capture booklice is required.

RESULTS

We here identified a new attractant, 2,3,5,6-tetramethylpyrazine (TMP), which efficiently captured booklice in combination with UV light. When booklice placed at both right and left edges of an assay tray were exposed to light stimulus from the center, test insects gathered at the center. The attraction was stronger with shorter wavelengths than longer ones: 365-nm ultraviolet (UV) light showed the strongest attraction of four tested light wavelengths. We found that cocoa powder attracted booklice weakly but significantly under total darkness. Furthermore, the cocoa smell was confirmed to enhance the attraction to light at all tested wavelengths irrespective of the difference between two brands of cocoa powders. Gas chromatography-mass spectrometry indicated that both cocoa products contain TMP as a major odor compound. Exposure of booklice to TMP significantly enhanced the attraction to UV light: the combined use with TMP almost doubled the attraction compared to the light only. By contrast, TMP homologs, pyrazine and dimethylpyrazines, showed strong repellent activities under UV light exposure.

CONCLUSION

TMP enhanced the UV light attraction for booklice while pyrazine and dimethylpyrazines diminished it. Use of these attractant and repellent pyrazine derivatives together with UV light would enable us to develop a practical new way to monitor and capture booklice. © 2023 Society of Chemical Industry.

Plant volatiles mediated the orientation preference of slugs to different plant species

BACKGROUND

Slugs mechanically damage plant leaves, resulting in significant economic losses. However, there are limited cost-efficient strategies available in slug management. By studying how slugs utilize plant volatiles to locate host plants, we can gain insights into the design of attractants and repellents.

RESULTS

Bioassay results suggest slugs (Agriolimax agrestis) prefer to orientate to lettuce (Lactuca sativa), cabbage (Brassica oleracea L.), and young tobacco seedlings, compared with old tobacco seedlings. We analyzed the volatomics of lettuce, cabbage, young and old tobacco seedlings. 2-(2-butoxyethoxy)-ethanol acetate (2EA) had high abundance while nonanal, decanal, and β-cylocitral had relatively low content in volatiles. Old tobacco seedlings released significantly more hexanal but fewer 1,4-dihydro-4-oxopyridazine (DO). In olfactory tests, hexanal, nonanal, decanal, and β-cylocitral showed strong repellency to slugs, while DO at a dose of 500 ng/μL and 2EA at a dose of 1% were attractive to slugs. The two alkanes, hexadecane and heptadecane, had no effect on slug orientating to host plants. DO and 2EA can thus alleviate the repellency of hexanal, nonanal, decanal and β-cylocitral.

CONCLUSION

The high emission of hexanal in old tobacco seedlings helps repel slugs, while 2EA and DO attract slugs to lettuce and cabbage. These findings suggest that these chemicals can be utilized in the design of repellents and attractants, and contribute to constructing a push-pull system for slug control. © 2023 Society of Chemical Industry.

The Plant Volatile-Sensing Mechanism of Insects and Its Utilization

Plants and insects are engaged in a tight relationship, with phytophagous insects often utilizing volatile organic substances released by host plants to find food and egg-laying sites. Using plant volatiles as attractants for integrated pest management is vital due to its high efficacy and low environmental toxicity. Using naturally occurring plant volatiles combined with insect olfactory mechanisms to select volatile molecules for screening has proved an effective method for developing plant volatile-based attractant technologies. However, the widespread adoption of this technique is still limited by the lack of a complete understanding of molecular insect olfactory pathways. This paper first describes the nature of plant volatiles and the mechanisms of plant volatile perception by insects. Then, the attraction mechanism of plant volatiles to insects is introduced with the example of Cnaphalocrocis medinalis. Next, the progress of the development and utilization of plant volatiles to manage pests is presented. Finally, the functions played by the olfactory system of insects in recognizing plant volatiles and the application prospects of utilizing volatiles for green pest control are discussed. Understanding the sensing mechanism of insects to plant volatiles and its utilization will be critical for pest management in agriculture.

How Effective Are Push-Pull Semiochemicals as Deterrents for Bark Beetles? A Global Meta-Analysis of Thirty Years of Research

Bark beetles (Coleoptera: Curculionidae: Scolytinae) are among the most damaging tree pests globally. Rising temperatures, drought, fire, storms, cyclones, and poor forest management cause stress and loss of vigour in trees, and these conditions favour bark beetle outbreaks. While research has been conducted on push-pull strategies to deter bark beetles, using attractive and deterrent semiochemicals, the potential of this strategy to reduce bark beetle populations, particularly in the genera Dendroctonus and Ips, remains uncertain. Here, we conducted a global meta-analysis of 52 research articles to quantify the effects of semiochemical treatments on managing different species of Dendroctonus and Ips for forest protection. Based on this analysis, we found that push-pull semiochemicals can significantly reduce Dendroctonus and Ips populations measured by a reduction in the attraction to lure/trap catches, tree mortality, and attacks on trees. The overall efficacy of the push-pull semiochemical treatment shows a 66% reduction for Ips compared to control and a 54% reduction compared to control for Dendroctonus, while, at the species level, there was a 69% reduction for Dendroctonus ponderosae (Hopkins) and a 94% reduction in Ips perturbatus (Eichhoff), and a 93% reduction in Ips latidens (LeConte). Interestingly, among different treatment sources, the efficacy of conspecific semiochemicals in combination with heterospecific semiochemicals and non-host volatiles showed a 92% reduction in Dendroctonus spp., and conspecific semiochemicals in combination with non-host volatiles showed a 77% significant reduction in Ips spp., while the efficacy of heterospecific semiochemicals in reducing Ips population was about 69%, and 20% in Dendroctonus. Among different ecological regions, the use of a push-pull strategy showed a 70% reduction in Dendroctonus in central-west North America, and Ips showed a 75% reduction in southwest North America. Our results demonstrate that semiochemical-based push-pull techniques have the potential to reduce Dendroctonus and Ips bark beetle populations. Furthermore, based on our analysis, the efficacy of such eco-friendly interventions could be further improved and provide a good tool for forest managers to control these pests, at least under some circumstances.

Peer review of the pesticide risk assessment of the active substance urea

The conclusions of the European Food Safety Authority (EFSA) following the peer review of the initial risk assessments carried out by the competent authorities of the rapporteur Member State Greece and co-rapporteur Member State Finland for the pesticide active substance urea and the considerations as regards the inclusion of the substance in Annex IV of Regulation (EC) No 396/2005 are reported. The context of the peer review was that required by Commission Implementing Regulation (EU) No 844/2012, as amended by Commission Implementing Regulation (EU) No 2018/1659. The conclusions were reached on the basis of the evaluation of the representative uses of urea as an attractant of fruit fly Bactrocera oleae on olive crops. The reliable end points, appropriate for use in regulatory risk assessment are presented. Missing information identified as being required by the regulatory framework is listed. Concerns are reported where identified.

Characterisation of Antennal Sensilla and Electroantennography Responses of the Dung Beetles Bubas bison, Onitis aygulus and Geotrupes spiniger (Coleoptera: Scarabaeoidea) to Dung Volatile Organic Compounds

Locating sporadically distributed food resources and mate finding are strongly aided by volatile cues for most insects, including dung beetles. However, there is limited information on the olfactory ecology of dung beetles. We conducted a scanning electron microscopy study on the morphology and distribution of the antennal sensilla of three introduced dung beetle species in Australia: Geotrupes spiniger (Coleoptera: Geotrupidae), Bubas bison and Onitis aygulus (Coleoptera: Scarabaeidae). Three main morphological types of antennal sensilla were identified: sensilla trichodea (ST), sensilla basiconica (SB) and sensilla chaetica (SCh). Distinct variations of SB distribution were observed in B. bison and G. spiniger and on different lamellar surfaces in both sexes of all three species. Sexual dimorphism in antennal sensilla distribution or their abundance was not evident. To complement the morphological characterisation of sensilla, electroantennography (EAG) was carried out to construct EAG response profiles of the three species to selected dung volatiles. An initial study revealed that antennae of all species were sensitive to a mix of phenol, skatole, indole, p-cresol, butanone and butyric acid, common components of livestock dung headspace. In addition to these six compounds, dimethyl sulfide, dimethyl disulfide, eucalyptol and toluene were tested for antennal activity. All compounds evoked measurable EAG responses, confirming antennal sensitivity. Geotrupes spiniger exhibited significant responses to all the compounds compared to the control, whereas B. bison and O. aygulus only responded to a subset of compounds. A comparison of relative EAG amplitudes revealed highly significant responses to p-cresol in G. spiniger and to skatole in B. bison. Geotrupes spiniger displayed differential responses to all the compounds. Pooled EAG data suggest highly significant differences in responses among the three species and among compounds. Our findings suggest that a blend of volatiles may offer potential for the trapping of dung beetles, thereby avoiding the use of dung baits that are inconvenient, inconsistent and may pose a threat to farm biosecurity.

Estragole, a potential attractant of the winged melon aphid Aphis gossypii

BACKGROUND

Aphids are sap-sucking insect pests of economic importance. They exhibit polyphenism, producing two kinds of morphotypes; winged (alate) and wingless (aptera) morphs. While wingless morphs can be controlled by insecticides, winged morphs are a challenge for targeted control measures as they can fly. Although colored sticky traps are used to control and monitor winged aphids, only a small population is trapped, making sticky traps less effective in controlling aphids. Studies have shown that fragrant oils applied to sticky traps increased attraction of sap-sucking insects like whiteflies and thrips. Here, we tested selected essential oils for their attractiveness to winged Aphis gossypii in potato fields.

RESULTS

In field assays, selected essential oils with yellow or colorless sticky traps attracted more winged A. gossypii than controls. The combination of yellow traps baited with essential oils attracted ~2-3-fold more winged A. gossypii than did colorless traps baited with essential oils. In a multi-cycle 2 year study, yellow sticky traps baited with basil oil consistently attracted more winged A. gossypii than yellow sticky traps baited with lavender, geranium or tea tree oils. In electrophysiological studies, winged A. gossypii's antennae responded consistently to estragole in basil oil. In olfactometer assays with estragole, winged A. gossypii spent significantly more time in the treatment arm of the olfactometer than in the control arm, validating estragole's attractiveness. Furthermore, yellow sticky traps baited with pure estragole, in potato fields, attracted similar number of winged A. gossypii as yellow sticky traps baited with basil oil.

CONCLUSION

Our findings demonstrate the potential of using basil oil as a potential attractant to improve the efficacy of sticky traps in the monitoring and control of winged aphids. © 2023 Society of Chemical Industry.

Electrophysiological and Behavioral Responses of Virgin Female Bactrocera tryoni to Microbial Volatiles from Enterobacteriaceae

The Queensland fruit fly (Bactrocera tryoni) is a major polyphagous pest widespread in Australia and several Pacific Islands. Bacteria present on the host plant phyllosphere supply proteins, essential for egg development and female sexual maturity. We investigated the role of microbial volatile organic compounds (MVOCs) emitted by Enterobacteriaceae commonly found on the host plant and in the fly gut in attracting virgin females. Bacteria were cultured on artificial media and natural fruits, at various pH, and MVOCs were collected using different headspace volatile absorbent materials. The olfactory responses of virgin females to bacterial MVOCs were assessed via electrophysiology and behavioral assays. The production of MVOCs was strongly influenced qualitatively by the bacterial strain and the type of media, and it semi-quantitatively varied with pH and time. MVOCs emitted by Klebsiella oxytoca invoked the strongest antennal response and were the most attractive. Among the identified compounds triggering an olfactory response, D-limonene and 2-nonanone were both significantly behaviorally attractive, whereas phenol, nonanal, isoamyl alcohol, and some pyrazines appeared to be repulsive. This study deepens our understanding of the chemical ecology between fruit flies and their bacterial symbionts and paves the way for novel synthetic lures based on specifically MVOCs targeting virgin females.

Peer review of the pesticide risk assessment of the active substance hydrolysed proteins

The conclusions of EFSA following the peer review of the initial risk assessments carried out by the competent authorities of the rapporteur Member State Spain and co-rapporteur Member State Greece for the pesticide active substance hydrolysed proteins and the considerations as regards the inclusion of the substance in Annex IV of Regulation (EC) No 396/2005 are reported. The context of the peer review was that required by Commission Implementing Regulation (EU) No 844/2012, as amended by Commission Implementing Regulation (EU) No 2018/1659. The conclusions were reached on the basis of the evaluation of the representative uses of hydrolysed proteins as an insect attractant on olive tree, deciduous fruit tree, stone fruit tree, pome fruit tree, walnut tree, citrus tree, fig tree, persimmon tree, kiwi and blueberry crops. The reliable end points, appropriate for use in regulatory risk assessment, are presented. Missing information identified as being required by the regulatory framework is listed. Concerns are reported where identified.

Function of environment-derived male perfumes in orchid bees

Perfume making in male orchid bees is a unique behavior that has given rise to an entire pollination syndrome in the neotropics.^1,2 Male orchid bees concoct and store species-specific perfume mixtures in specialized hind-leg pockets³ using volatiles acquired from multiple environmental sources, including orchid flowers.^4,5 However, the function and the ultimate causes of this behavior have remained elusive.^2,6 Although previous observations suggested that male perfumes serve as chemical signals, the attractiveness for females has not be shown.^7,8 Here, we demonstrate that the possession of perfume increases male mating success and paternity in Euglossa dilemma, a species of orchid bees recently naturalized in Florida. We supplemented males reared from trap-nests with perfume loads harvested from wild conspecifics. In dual-choice experiments, males supplemented with perfumes mated with more females, and sired more offspring, than untreated, equal-aged, control males. Although perfume supplementation had little effect on the intensity of male courtship display, it changed the dynamics of male-male interactions. Our results demonstrate that male-acquired perfumes are sexual signals that stimulate females for mating and suggest that sexual selection is key in shaping the evolution of perfume communication in orchid bees.

Potential of 3-octanone as a lure and kill agent for control of the Brown Garden Snail

The brown garden snail (Cornu aspersum) is a major agricultural pest, causing damage to a wide range of economically important crops. Withdrawal or restricted use of pollutant molluscicides like metaldehyde has prompted a search for more benign control products. This study investigated the response of snails to 3-octanone; a volatile organic compound (VOCs) produced by the insect pathogenic fungus Metarhizium brunneum. Concentrations of 1 - 1000 ppm of 3-octanone were first assessed in laboratory choice assays to determine behavioural response. Repellent activity was found at 1000 ppm whereas attractance was found for the lower concentrations of 1, 10 and 100 ppm. These three concentrations 3-octanone were carried forward in field evaluations to assess potential for use in "lure and kill" strategies. The highest concentration (100 ppm) was the most attractive to the snails but also the most lethal. Even at the lowest concentration this compound proved toxic making 3-octanone an excellent candidate for the development as a snail attractant and molluscicide.

Non-host plant odors influence the tritrophic interaction between tomato, its foliar herbivore Tuta absoluta and mirid predator Nesidiocoris tenuis

The tomato leafminer, Tuta absoluta is a destructive invasive pest of cultivated tomato and other Solanaceae plants, with yield losses of 80-100%. Mirid predators are key natural enemies of T. absoluta, but they also feed on host plants in the absence of their prey. Management of T. absoluta is a challenge due to its high biotic potential, resistance to many insecticides and the absence of sufficiently adapted auxiliary fauna in its new dispersion zones. Olfaction plays an important role in the tritrophic interaction between tomato, its herbivore pest T. absoluta and its mirid predators, which can be influenced by non-host plant odors. However, how non-host odours shape this interaction is poorly understood. Previously, we had demonstrated belowground crop protection properties of certain Asteraceae plants against the root-knot nematode Meloidogyne incognita, pest of tomato and other Solanaceae plants. Additionally, Asteraceae plants impact negatively on feeding behavior of above-ground pests of Solanaceae plants, including the greenhouse whitefly (Trialeurodes vaporariorum) and green peach aphid (Myzus persicae). Here, we tested the hypothesis that foliar volatiles from some of these non-host Asteraceae plants can influence the tomato-T. absoluta-mirid predator tritrophic interaction. In olfactometer assays, T. absoluta females were attracted to volatiles of the Solanaceae host plants tomato and giant nightshade but avoided volatiles of the Asteraceae plants, blackjack and marigold, and the positive control, wild tomato, when tested alone or in combination with the host plants. Coupled gas chromatography-mass spectrometry analysis showed that host and non-host plants varied in their emission of volatiles, mainly monoterpenes and sesquiterpenes. Random forest analysis combined with behavioral assays identified monoterpenes as the host plant attractive blend to T. absoluta and its mirid predator, with sesquiterpenes identified as the non-host plant repellent blend against T. absoluta. Contrastingly, the mirid predator was indifferent to the non-host plant repellent sesquiterpenes. Our findings indicate that terpenes influence the tomato-T. absoluta-mirid predator tritrophic interaction. Further, our results emphasize the importance of studying crop protection from a holistic approach to identify companion crops that serve multi-functional roles.

Preparation and evaluation of attractive microspheres for control of Agrilus planipennis fairmaire

Agrilus planipennis Fairmaire is an important wood boring pest of Fraxinus species in the family Oleaceae. Oxacyclotridecan-2-one is an attractant of A. planipennis. Traps with attractive lures can be used in mass trapping of insect pests, but the traps are a bit expensive and they must be set up and dismantled in the field. To develop an attract and kill method for A. planipennis, we enveloped oxacyclotridecan-2-one into sustained-released microspheres. The attractant microspheres were prepared using the solvent evaporation method. An orthogonal test L₁₆(4⁵) was used to optimize the five preparation factors: the quantities of polylactic acid (PLA), gelatin, Polyvinyl alcohol (PVA), attractant, and the rotational speed. The results showed that optimal conditions for preparation of microspheres were 2.5 g PLA, 0.5 g gelatin, 1.25 g PVA, 2 mL attractant and 600 r min^-1 rotational speed. The encapsulation efficiency of the prepared microspheres was 95.22%, and the attractant loading rate was 15.61%. The release rate of attractant from prepared microspheres was about 26.74% on the first day, and then gradually entered a sustained-release stage for about 10 days that lasted for 17 days. Preliminary field control experiments showed that the prepared microspheres could attract and kill A. planipennis adults when sprayed together with insecticide.

Feeding Preferences and Responses of Monochamus saltuarius to Volatile Components of Host Pine Trees

Monochamus saltuarius is a vector of Bursaphelenchus xylophilus and has caused massive mortality in pine trees in Japan, South Korea, and the middle temperate zone of China. In this study, the feeding preferences of M. saltuarius to four common host pine species in the middle temperate zone of China were investigated in a laboratory. The volatiles of the four host pine species were sampled and analyzed by gas chromatography and mass spectrometry. The responses of M. saltuarius to host pine tree volatiles were measured using a four-arm olfactometer. The results showed that: (1) the preference of M. saltuarius for Pine tabulaeformis was significantly higher than the other ones. (2) The composition and content of the volatiles of the four tested host pine twigs were different, and the relative content of α-pinene was the highest. (3) M. saltuarius was highly sensitive to α-pinene, β-pinene, limonene, and 3-carene, and the attracting effect was enhanced by the mixture of volatile components. This study provides a reference for the development and application of attractants for M. saltuarius. Our results would be helpful in controlling M. saltuarius and pine wilt disease.

Discovery of a New Chemoeffector for Escherichia coli Chemoreceptor Tsr and Identification of a Molecular Mechanism of Repellent Sensing

Motile bacteria use chemotaxis to search for nutrients and escape from harmful chemicals. While the sensing mechanisms for chemical attractants are well established, the molecular details of chemorepellent detection are poorly understood. Here, by using combined computational and experimental approaches to screen potential chemoeffectors for the Escherichia coli chemoreceptor Tsr, we identified a specific chemorepellent, 1-aminocyclohexanecarboxylic acid (ACHC). Our study strongly suggests that ACHC directly binds to the periplasmic sensory domain of Tsr and competes with l-serine, the amino acid attractant of Tsr. We further characterized the binding features of l-serine, ACHC, and l-leucine (a natural repellent that binds Tsr) and found that Asn68 plays a key role in mediating chemotactic response. Mutating Asn68 to Ala inverted the response to l-leucine from a repellent to an attractant. Our study provides important insights into the molecular mechanisms of ligand sensing via bacterial chemoreceptors.

Toward Chemical Ecology of Plant-Parasitic Nematodes: Kairomones, Pheromones, and Other Behaviorally Active Chemical Compounds

An overview of natural chemical compounds involved in plant-parasitic nematode (PPN) behavior is presented and classified following a system accepted by chemoecologists. Kairomonal and other egg-hatching stimulants, as well as attractants for juveniles, are presented. Sex, aggregation, egg-hatching, and putative diapause PPN pheromones are analyzed and grouped into clusters of primers and releasers. The role of over 500 chemical compounds, both organic and inorganic, involved in PPN behavior is reviewed, with the most widely analyzed and least studied fields of PPN chemical ecology indicated. Knowledge on PPN chemical ecology facilitates environmentally friendly integrated pest management. This could be achieved by disrupting biointeractions between nematodes and their host plants and/or between nematodes. Data on biologically active chemicals reveals targets for resistant plant selection, including through application of gene silencing techniques.

Effects of diluted Concord grape juice laced with sodium chloride and selected boron-containing compounds on attraction, consumption, crop muscle contractions, and mortality of adult Drosophila suzukii Matsumura (Diptera: Drosophilidae)

BACKGROUND

In recent years, there has been interest in low-cost, reduced-risk materials that could be used for attract-and-kill of the invasive pest, spotted-wing Drosophila, Drosophila suzukii. This pest causes heavy economic damage to soft-skinned fruits in many countries. In this study, we evaluated physiological and behavioral effects of adding either borax, boric acid, or sodium chloride to diluted Concord grape juice (DGJ), a material that is attractive to adult D. suzukii.

RESULTS

Results showed that the addition of borax, sodium chloride and boric acid did not significantly affect the response of adult D. suzukii, relative to DGJ alone. Increases in concentrations (to 5% and 10%) of borax, sodium chloride and boric acid were correlated with decreased ingestion of materials. Mortality of males and females was almost 100% with lower concentrations (1% and 5%) of borax and boric acid within 72 h. The higher concentrations of sodium chloride (5% and 10%) resulted in 100% mortality of both sexes within 72 h. There was no significant effect of chemicals on the number of crop contractions of flies when fed for 4 h.

CONCLUSIONS

This study suggests that some substances such as boric acid and borax may act as toxicants without influencing the behavioral response of D. suzukii. © 2021 Society of Chemical Industry.

Development of Sustainable Chemistry in Madagascar: Example of the Valuation of CNSL and the Use of Chromones as an Attractant for Mosquitoes

This article describes a part of the results obtained from the cooperation between the University of Lyon1 (France) and the University of Antananarivo (Madagascar). It shows (among others) that useful research can be carried out in developing countries of the tropics if their social, technical, and economic conditions are taken into account. The concepts and methods associated with so-called “green chemistry” are particularly appropriated for this purpose. To illustrate this approach, two examples are shown. The first deals with industrial ecology and concerns waste transformation from the production of cashew nut into an amphiphilic product, oxyacetic derivatives. This product was obtained with a high yield and in a single step reaction. It exhibited an important surfactant property similar to those of the main fossil-based ones but with a much lower ecological impact. The second talks about chemical ecology as an alternative to insecticides and used to control dangerous mosquito populations. New substituted chromones were synthesized and showed biological activities toward Aedes albopictus mosquito species. Strong repellent properties were recorded for some alkoxylated products if others had a significant attractant effect (Kairomone) depending on their stereochemistry and the length of the alkyl chain.

Addition of Ammonium Acetate to Protein-Borax Baited Traps Does Not Improve Attraction of Anastrepha obliqua or Anastrepha serpentina (Diptera: Tephritidae)

Ammonia is considered a key component in the attraction of tephritid flies to protein-based lures. The addition of ammonium acetate to improve hydrolyzed protein-borax mixtures used to monitor tephritids has not been evaluated, although it has improved attraction to toxic baits. The presence of ammonium acetate crystals in a ventilated tube inside a trap containing hydrolyzed protein + borax, did not improve the capture of Anastrepha obliqua or Anastrepha serpentina flies in field experiments when compared with hydrolyzed protein + borax alone. In contrast, the addition of 1% ammonium acetate into the drowning solution of a hydrolyzed protein + borax mixture resulted in significantly reduced captures of both pests. Laboratory tests indicated that the emission of ammonia gas was increased 1.6-4.5-fold from traps that included ammonium acetate. These results confirm the hypothesis that a higher release of ammonia does not improve the attraction of tephritids when protein-derived odors are also present.

Synthesis and activity of 3-oxo-α-ionone analogs as male attractants for the solanaceous fruit fly, Bactrocera latifrons (Diptera: Tephritidae)

A series of 3-oxygenated α-ionone analogs have been developed as highly specific male lures for the solanaceous fruit fly Bactrocera latifrons, a pest of solanaceous fruits. We compared the attractant and phagostimulant activities of analogs with or without (i) unsaturations at the 4,5- and/or 7,8-positions and (ii) oxygen moieties at the 3- and/or 9-positions of the ionone molecule. Since naturally occurring vomifoliol (V2) was found to induce a highly potent phagostimulant activity in B. latifrons males, related analogs including, dehydrovomifoliol (V1), 6-hydroxy-α-ionone (U1) and 6-hydroxy-α-ionol (U2) were synthesized to evaluate their attractant and phagostimulant activities. Synthetic V1, V2, U1 and U2 exhibited low attractant activity, but their phagostimulant activity was relatively high. Optical isomers of 3-oxo-7,8-dihydro-α-ionone (P3) and V1 were prepared to examine the stereochemical specificity of attractants. (+)-(6R)-P3 and (+)-(6S)-V1 exhibited the corresponding activities, while their respective antipodal enantiomers were found entirely inactive.

Sex Pheromone of the Introduced Pine Sawfly, Diprion similis, Revisited to Define a Useful Monitoring Lure: Deviating Chiral Composition and Behavioural Responses Compared to Earlier Reports

Extracts of Diprion similis females contained about 15 ng of the sex pheromone precursor 3,7-dimethylpentadecan-2-ol per female. After derivatisation with (S)-2-acetoxypropanoyl chloride, we found that the major stereoisomer in the extract was (2S,3R,7R)-3,7-dimethylpentadecan-2-ol. Small amounts of other stereoisomers of 3,7-dimethylpentadecan-2-ol were also identified in the extract, namely 1% of (2R,3S,7S), 0.3% (2R,3R,7R) and 0.4% of (2R,3R,7S). An unknown fifth substance showed a very similar spectrum to 3,7-dimethylpentadecan-2-ol, both in SIM and full scan mode. None of the earlier suggested behavioural synergistic isomers ((2S,3S,7S), (2S,3S,7R) and (2S,3R,7S)) were detected in the extracts. In field tests in Ontario, Canada, the earlier identified main pheromone component, viz. the propanoate of (2S,3R,7R)-3,7-dimethylpentadecan-2-ol, was tested alone and in combination with other stereoisomers, earlier reported to be synergistic. No synergistic effects were detected and the threo four-isomer blend was as attractive as the pure main compound. Thus, one of the few examples of a diprionid sawfly using more than one substance in its sex pheromone could not be confirmed. The results also suggest that monitoring programs can use the more easily synthesized threo-blend without losing efficiency. Furthermore, the study suggests that other diprionid pheromones may benefit from a reinvestigation, to clarify possible synergistic effects of stereoisomers.

Laboratory and Field Evaluations of Food-Based Attractants for Monitoring German Cockroaches

Sticky traps are standard tools for monitoring German cockroaches (Blattella germanica L.); however, because they lack an attractant, their ability to catch cockroaches is by chance and largely dependent upon the location of placement and length of time they are left in place. Currently, highly effective and economical cockroach attractants are not available. Food-based attractants have the potential to be employed in sticky traps and enhance their effectiveness on trapping German cockroaches. We conducted laboratory and field experiments to evaluate the effectiveness of novel food-based attractants. Laboratory results showed that sticky traps containing the following attractants: apple oil, blueberry oil, orange oil, or their combination, fish oil, peanut butter, Roach lure tablet, and bacon extract had significantly higher trap catch compared to those traps that do not contain an attractant. Apple plus blueberry oil mixture and Roach lure tablet enhanced the trap catch by ≥ 103%, and bacon extract enhanced the trap catch by 92% in the field assays. Apple plus blueberry oil mixture and Roach lure tablet were the most promising attractants based on laboratory and field experiments. Apple plus blueberry oil mixture aged for 2 wk was as attractive to German cockroaches as fresh mixture.

and Anopheles minimus Theobald (Diptera: Culicidae)

Several types of olfactometers have been used to evaluate mosquito responses to agents that mimic natural volatiles that repel or attract. The Y-tube olfactometer has been widely used to study repellents and attractants, while the high-throughput screening system assay has only been used to study repellents. Whether the high-throughput screening system assay is suitable for evaluating attractants is unknown. We evaluated the responses to four lactic-acid-based mixtures and two non-lactic-acid-based chemical lure candidates using the high-throughput screening system (HITSS) for three mosquito species (laboratory strains and field populations of both Aedes aegypti (L.) and Culex quinquefasciatus Say.; laboratory strain of Anopheles minimus Theobald) under laboratory-controlled conditions. HITSS assay results showed that KU-lure #1 elicited the greatest percent attraction for pyrethroid-resistant and -susceptible Ae. aegypti. KU-lure #6 elicited the strongest attractive response for pyrethroid-susceptible and -resistant Cx. quinquefasciatus and pyrethroid-susceptible An. minimus. The response to the lures from each species was independent of the pyrethroid susceptibility status (Ae. aegypti, p = 0.825; Cx. quinquefasciatus, p = 0.056). However, a significant difference in attraction to KU-lure #6 was observed between diurnal and nocturnal mosquitoes (Cx. quinquefasciatus vs. Ae. aegypti, p = 0.014; An. minimus vs. Ae. aegypti, p = 0.001). The laboratory-level HITSS assay effectively selects potential lure candidates. Because the host-seeking behavior differs between mosquito species, further studies are needed to develop species-specific attractants. Additional studies in semi-field screen houses using commercial traps are necessary to evaluate the accuracy of these laboratory assay results.

Diel Rhythmicity of Field Responses to Synthetic Pheromone Lures in the Pine Sawyer Monochamus saltuarius

Simple Summary

Monochamus saltuarius is a vector of pine wood nematode (PWN) in Korea and eastern China. The diel rhythmicity of M. saltuarius in response to an aggregation pheromone and attractants (PA) was studied with the aid of a spray device controlled with an electronic timer. Our study revealed that the flight activity of M. saltuarius in response to PA was diurnal. The results improve the understanding of the behavioral biology of M. saltuarius, allowing the development of pest management strategies to prevent the spread of PWN and control its vector.

Abstract

The pine wood nematode (PWN), Bursaphelenchus xylophilus, causes lethal pine wilt disease (PWD) in Asia and Europe and has become a serious threat to global pine forest ecosystems. In Korea, Monochamus saltuarius transmits PWN not only to Pinus densiflora, but also to Pinus koraiensis, which is widely distributed across eastern Asia. The diel rhythmicity of M. saltuarius in response to its aggregation pheromone was studied with the aim of providing reliable data for the prevention of PWD and control of Monochamus spp. Using a spray dispenser controlled with an electronic timer, M. saltuarius pheromone and attractants (PA) were sprayed to determine the diel rhythm of the response to PA. The spraying period was divided into four time periods: 05:00–11:00 (time period A), 11:00–17:00 (time period B), 17:00–23:00 (time period C), and 23:00–05:00 (time period D). The largest number of M. saltuarius was caught in time period B, followed by A, C, and D. It could be concluded that the flight activity of M. saltuarius in response to PA was diurnal. The results of this study improve the understanding of the behavioral biology of M. saltuarius, allowing for the development of pest management strategies to prevent the spread of PWN and control its vector.

Dose-Response Assay for Synthetic Mosquito (Diptera: Culicidae) Attractant Using a High-Throughput Screening System

Simple Summary

Entomological surveillance is important to evaluate vector management interventions. However, collecting adult mosquitoes using direct human bait is controversial and often discouraged because of potential infection risk. Alternatively, active and passive trapping methods are available. Female mosquitoes detect human host cues such as body heat, carbon dioxide, and other volatile body emanations using olfactory sensilla to direct movement to a host. Attractive chemical lures have been identified and evaluated using a variety of olfactometric methods to increase trap production and efficiency. In this study, we evaluated a simple olfactometer without need of airflow. To ‘optimize’ a commercial mosquito attractant, 10 different doses of product, the Biogents-lure (BG-lure^TM), were compared. Results showed dose-dependent responses with 0.005 g with the highest attraction for Aedes aegypti, while doses of 0.2 g and above produced a repellent response. There was no significantly different response behavior between permethrin-susceptible and -resistant Ae. aegypti. Culex quinquefasciatus showed significantly different responses compared to Ae. aegypti by producing attraction over four times a wider range of amounts. These results demonstrate a simple olfactometer device to screen potential chemical attractants without use of an air-plume, thus expanding testing capabilities beyond more sophisticated laboratory settings.

Abstract

Natural volatile host cues play a critical role for mosquito orientation and locating a blood source for egg production. Similar olfactory activation responses have allowed the use and development of artificial chemical attractants to lure mosquitoes to trapping devices. Using a pre-formulated commercial product mixture of different attractant chemicals, a high-throughput screening system (HITSS) is used to screen varying doses of chemical required to activate behavioral responses. Two strains of Aedes aegypti (L.): permethrin-susceptible (USDA) and -resistant (Pu Teuy) phenotypes and one Culex quinquefasciatus Say. (NIH) laboratory strain were tested. Overall, mosquitoes showed repellency between 1.0 g and to 10.0 g dose of each compound. However, by progressively reducing the dose, Cx. quinquefasciatus showed a greater positive percent attraction (88.9%) at 0.025 g, whereas the USDA and Pu Teuy Ae. aegypti produced optimum attractant activation at 0.005 g (72.6% and 58.9%, respectively) without significant difference within species (p > 0.05). In parallel control assays, Cx. quinquefasciatus was significantly attracted to 1 g of dry ice (carbon dioxide) (76%) more than Ae. aegypti (USDA) (12.2%). The HITSS was originally designed to measure three chemical actions to sublethal concentrations of chemicals by mosquitoes: toxicity and the two primary behavior avoidance responses (contact excitation and spatial repellency). These findings demonstrate that the HITSS assay, with only minor modifications, allows comparison screening of candidate compounds as potential attractants for anemotactic responses under laboratory-controlled conditions. Further investigations will be required to equate measurements obtained from controlled laboratory assays to more varied field conditions for attracting natural mosquito populations.

Are Yeast Autolysate Attractants for Ceratitis Species (Diptera: Tephritidae) in South Africa More Attractive and Palatable Than a Currently Used Protein Attractant?

Due to increasing usage of copper fungicides in citrus orchards shortly before the application of protein baits for fruit fly control and the risk of this combination causing fruit phytotoxicity, an investigation of attractants containing higher amounts of yeast autolysate rather than protein hydrolysate was conducted. A commercial yeast autolysate from Australia was less attractive than a South African product HymLure (with a mixture of autolysate and hydrolysate) to three Ceratitis species: Ceratitis capitata (Wiedemann), Ceratitis rosa s.s. Karsch, and Ceratitis cosyra (Walker). Other custom-formulated autolysates were also inferior to HymLure for these species. Consumption of autolysates during the first hour of feeding was similar to that of HymLure. The inferior attraction of these three species of fruit flies to autolysates, relative to one containing hydrolysate, did not warrant further investigation of autolysates for use in baits to control these quarantine pests.

Analyses of structural dynamics revealed flexible binding mechanism for the Agrilus mali odorant binding protein 8 towards plant volatiles

BACKGROUND

Volatiles from host plants are an important source of insect pest attractants and repellents. Insect odorant binding proteins (OBPs) have been widely characterized, but the molecular binding dynamics and underlying mechanisms are still not well understood. Thus, we characterized binding characteristics of AmalOBP8 from the apple buprestid beetle (Agrilus mali Matsumura), an unprecedented serious threat to rare apple germplasm resources and local ecosystems.

RESULTS

Fluorescence studies demonstrated that the quenching mechanism was clearly static. AmalOBP8 was found to bind with both volatiles at single independent sites. Negative thermodynamic parameters suggested that binding interactions between AmalOBP8 and both volatiles could occur spontaneously. Hydrogen bonding was the key force in AmalOBP8's binding to geranyl formate, for which the amino acid residue Trp106 played a critical role in the binding pocket. Multiple Leu residues in AmalOBP8 created a strong hydrophobic environment, and formed the binding pocket for (Z)-3-hexenyl hexanoate. Compared to classic OBPs, in addition to lack of one disulfide bridge, AmalOBP8 had a small α-helix (α7) at the C-terminus, resulting in greater flexibility and adaptability for this protein to bind with different compound molecules.

CONCLUSION

Key residues of AmalOBP8 in binding interactions with plant volatiles were clarified. AmalOPB8 had a large ligand binding spectrum and great flexibility in binding with plant volatiles, providing good molecular targets for screening insect attractants and repellents. Our results can promote understanding of insects' perception of various odorants, and establish a foundation for discovery of new pest control agents. © 2020 Society of Chemical Industry.

Calcium sulfate and calcium carbonate as root-knot-nematode attractants and possible trap materials to protect crop plants

Root-knot nematodes (RKNs, genus Meloidogyne) are a class of plant parasites that seek out and infect the roots of many plant species. The identification of RKN attractants can be used in agriculture in conjunction with nematode-trapping technology to redirect RKN movements and eventually reduce their prevalence in the field. Here, we discovered that some commercial silica gels can attract nematodes. Silica gels that attract nematodes contain calcium sulfate. Calcium sulfate and calcium carbonate showed strong nematode attraction properties. When plant seeds were surrounded by calcium sulfate or calcium carbonate, nematodes were not attracted to the plant seeds. We propose that calcium sulfate and calcium carbonate can be used in agriculture as a novel material to trap RKN.

Mosquito Attractants

Vector control and personal protection against anthropophilic mosquitoes mainly rely on the use of insecticides and repellents. The search for mosquito-attractive semiochemicals has been the subject of intense studies for decades, and new compounds or odor blends are regularly proposed as lures for odor-baited traps. We present a comprehensive and up-to-date review of all the studies that have evaluated the attractiveness of volatiles to mosquitoes, including individual chemical compounds, synthetic blends of compounds, or natural host or plant odors. A total of 388 studies were analysed, and our survey highlights the existence of 105 attractants (77 volatile compounds, 17 organism odors, and 11 synthetic blends) that have been proved effective in attracting one or several mosquito species. The exhaustive list of these attractants is presented in various tables, while the most common mosquito attractants - for which effective attractiveness has been demonstrated in numerous studies - are discussed throughout the text. The increasing knowledge on compounds attractive to mosquitoes may now serve as the basis for complementary vector control strategies, such as those involving lure-and-kill traps, or the development of mass trapping. This review also points out the necessity of further improving the search for new volatile attractants, such as new compound blends in specific ratios, considering that mosquito attraction to odors may vary over the life of the mosquito or among species. Finally, the use of mosquito attractants will undoubtedly have an increasingly important role to play in future integrated vector management programs.

Olfactory and behavioral responses to acetate esters in red imported fire ant, Solenopsis invicta

BACKGROUND

The red imported fire ant, Solenopsis invicta Buren, is one of the most successful invasive ants in the world. Previous studies indicated that benzyl acetate and prenyl acetate elicited significant electroantennography (EAG) response in S. invicta and exhibited as attractants at certain concentrations. In addition, the easy commercial availability, low cost, and low mammalian toxicity make acetate esters ideal candidates to screen for potential use in S. invicta control.

RESULTS

We examined the EAG and behavioral responses to 26 acetate esters in all castes of S. invicta. Our results demonstrated a large diversity of EAG tuning and behavioral responses to acetate esters in S. invicta. For linear alkyl acetate esters, EAG response was clearly affected by the carbon chain length of the alkyl group. Linear alkyl acetates with five to seven carbon chain length of the alkyl group elicited significant EAG response in S. invicta, whereas those with shorter (C1 to C4) or longer (C8 to C12) carbon chain lengths did not. Different substitutions also exhibited large variety of EAG and behavioral responses in S. invicta.

CONCLUSION

Our works explored the olfactory and behavioral response of S. invicta to structurally different acetate esters, and identified two potential fire ant attractants, pentyl acetate and tran-2-hexenyl acetate, and two potential repellents, hexyl acetate and cis-3-hexenyl acetate. These compounds may be useful in developing new products for fire ant management. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Multiple olfactory pathways contribute to the lure process of Caenorhabditis elegans by pathogenic bacteria

Chemosensation is indispensable for the survival of Caenorhabditis elegans to discriminate food and pathogenic bacteria in their living environment. Food-like odors emitted by the pathogen Bacillus nematocida B16 for trapping its hosts and an olfactory signaling pathway responsible to sense the attractant 2-heptanone were identified in our previous study. Here, we further explore how the worms recognize the attractive molecules indole and 2-ethyl hexanol, which have different chemical properties and modest nematode-luring ability. We show that the chemotaxis toward indole and 2-ethyl hexanol requires the G protein-coupled receptors encoded by str-193 on AWC and str-7 on AWA. In a further genetic screen for downstream effectors in olfactory signaling cascades, the Gα subunit GSA-1, guanylyl cyclase ODR-1 and DAF-11 and the cGMP-gated channel TAX-2/TAX-4 were found to be necessary for indole sensation, whereas the TRPV channels OSM-9/OCR-2 and the PLC pathway activated by GPA-6 are responsible for the detection of 2-ethyl hexanol. Altogether, our current work further clarifies the distinct olfactory signaling pathways through which C. elegans senses different chemicals and is lured by B. nematocida B16, improving our comprehensive understanding of the mechanisms by which bacterial pathogens effectively infect their hosts.

Comparative Trap Catches of Male Bactrocera, Dacus, and Zeugodacus Fruit Flies (Diptera: Tephritidae) With Four Floral Phenylbutanoid Lures (Anisyl Acetone, Cue-Lure, Raspberry Ketone, and Zingerone) in Queensland, Australia

The male fruit fly attractants, cue-lure (CL) and raspberry ketone (RK), are important in pest management. These volatile phenylbutanoids occur in daciniphilous Bulbophyllum Thouar (Orchidaceae: Asparagales) orchids, along with zingerone (ZN) and anisyl acetone (AA). While these four compounds attract a similar range of species, their relative attractiveness to multiple species is unknown. We field tested these compounds in two fruit fly speciose locations in north Queensland, Australia (Lockhart and Cairns) for 8 wk. Of 16 species trapped in significant numbers, 14 were trapped with CL and RK, all in significantly greater numbers with CL traps than RK traps (at least in higher population locations). This included the pest species Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (CL catches ca. 5× > RK), Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae) and Bactrocera bryoniae (Tryon) (Diptera: Tephritidae) (CL catches ca. 3× > RK), and Bactrocera frauenfeldi (Schiner) (Diptera: Tephritidae) (in Cairns-CL catches ca. 1.6× > RK). Seven species were trapped with AA, and all were also caught in CL and RK traps in significantly greater numbers, with the exception of B. frauenfeldi. For this species, catches were not statistically different with CL, RK, and AA in Lockhart, and RK and AA in Cairns. Seven species were trapped with ZN, two at this lure only, and the remainder also with CL or RK but in significantly greater numbers. This is the first quantitative comparison of the relative attractiveness of CL, RK, AA, and ZN against multiple species, and supports the long-held but untested assumption that CL is broadly more attractive lure than RK.

Chemosensory and Behavioural Responses of Ixodes scapularis to Natural Products: Role of Chemosensory Organs in Volatile Detection

Simple Summary

Ticks are responsible of transmitting serious disease agents of importance to human and veterinary health. Despite the importance of repellents, deterrents and acaricides in tick management, little is understood about the types of chemicals recognized and the mechanism behind chemoreception. Being almost totally blind, ticks rely on chemosensation to identify and locate hosts for a successful blood meal and to detect chemical signals in the environment. We explored the neurophysiology of tick chemosensory system in the context of behaviourally-relevant volatile stimuli, including essential oil components, to evaluate how the combination of attractants and plant volatile compounds is detected and processed. The observed inhibition (or deterrent effect) in tick electrophysiological response and behavioural activity, after the tick has been exposed to a binary mixture of attractant and volatile compound, represents an important advancement in understanding how tick olfaction works and what may be the mechanism behind detecting unpleasant odor stimuli and consequently been deterred. These information will provide more insights in developing new natural product-based deterrents for self-protection.

Abstract

Blacklegged ticks, Ixodes scapularis, represent a significant public health concern due to their vectoring of tick-borne disease. Despite their medical importance, there is still limited knowledge of the chemosensory system of this species, and thus a poor understanding of host-seeking behaviour and chemical ecology. We investigated the electrophysiological sensitivity of adult female blacklegged ticks to attractants and plant-derived compounds via an electrode inserted into the scutum. The response of female ticks to binary mixtures with a constant concentration of a selected attractant (butyric acid) and increasing concentration of volatile organic compounds (VOCs) (geraniol, phenethyl alcohol, β-citronellol, and citral) was recorded. A strict relationship between increasing volatile concentration and a decreasing response was observed for each VOC. Y-tube bioassays confirmed that tick attraction towards butyric acid decreased with the presence of a VOC, which exerted a deterrent effect. To determine the specific role of sensory appendages involved in the detection of attractant chemical stimuli, we tested tick electrophysiological response after removing appendages that house chemosensory sensilla (foretarsi, pedipalps, or both). The chemosensory response was related to the molecular structure of attractant odorant, and the lack of pedipalps significantly reduced olfactory responses, suggesting they play an important role in detecting attractants. This study provides new insight into the neurophysiological mechanisms underlying tick olfaction and the potential for interactions between attractant and deterrent chemical detection.

The Venom Compound N-(3-methylbutyl)acetamide Attracts Several Polistes (Fuscopolistes) Species (Hymenoptera: Vespidae)

Polistes paper wasps in the Fuscopolistes subgenus (Hymenoptera: Vespidae) can be serious pests when they swarm at tall man-made structures. Chemical attractants may be useful to trap such paper wasps when they achieve pest status. Polistes venom has been shown to elicit a variety of behavioral responses in congeneric wasps, making it a source for potential chemical attractants. The compound N-(3-methylbutyl)acetamide is a principal volatile component in the venom of many female vespid wasps, including numerous Polistes species. We report the presence of N-(3-methylbutyl)acetamide in autumn gynes of Polistes metricus Say, Polistes bellicosus Cresson, and Polistes dorsalis (F.), as well as workers of Polistes aurifer (Saussure), P. bellicosus, P. metricus, and P. dorsalis. In field tests conducted in Florida, Georgia, South Carolina, and Washington, N-(3-methylbutyl)acetamide attracted male and female P. aurifer and P. metricus, as well as male P. dorsalis and P. bellicosus. Thus, N-(3-methylbutyl)acetamide may be a useful lure for trapping these paper wasps in pest situations.

TLC-Based Bioassay to Isolate Kairomones from Tea Tree Essential Oil That Attract Male Mediterranean Fruit Flies, Ceratitis capitata (Wiedemann)

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) poses a major threat to fruit and vegetable production in the United States and throughout the world. New attractants and detection methods could improve control strategies for this invasive pest. In this study, we developed a method that combined thin-layer chromatography (TLC) of tea tree essential oil (TTO) (Melaleuca alternifolia) with short-range bioassays to isolate attractive kairomones for male C. capitata. After development, the TLC chromatogram indicated that TTO separated into five major spots, designated as zones 1 to 5. When the TLC plate was exposed to flies, zones 1 and 3 were strongly attractive to male C. capitata. To confirm activity, the developed TLC plate was cut into five zones which were then tested in short-range bioassays. Again, flies were observed to aggregate around zones 1 and 3, which corresponded with R_f values of 0.93 and 0.59. In addition, zones 1 to 5 were separated using preparative-TLC, and olfactory responses to volatile emissions from the five fractions were quantified by electroantennography (EAG). Highest amplitude EAG responses were recorded with fractions 1 and 3, further supporting the bioactivity of these samples. In conclusion, a TLC-based bioassay system can provide an effective, rapid screening protocol for initial isolation of insect kairomones from complex mixtures such as essential oils or plant extracts. Further analysis of TTO fractions 1 and 3 is needed to identify the specific constituents attractive to male C. capitata.

A Biomimetic Nanoparticle to "Lure and Kill" Phospholipase A2

Inhibition of phospholipase A2 (PLA2) has long been considered for treating various diseases associated with an elevated PLA2 activity. However, safe and effective PLA2 inhibitors remain unavailable. Herein, we report a biomimetic nanoparticle design that enables a "lure and kill" mechanism designed for PLA2 inhibition (denoted "L&K-NP"). The L&K-NPs are made of polymeric cores wrapped with modified red blood cell membrane with two inserted key components: melittin and oleyloxyethyl phosphorylcholine (OOPC). Melittin acts as a PLA2 attractant that works together with the membrane lipids to "lure" in-coming PLA2 for attack. Meanwhile, OOPC acts as inhibitor that "kills" PLA2 upon enzymatic attack. Both compounds are integrated into the L&K-NP structure, which voids toxicity associated with free molecules. In the study, L&K-NPs effectively inhibit PLA2-induced hemolysis. In mice administered with a lethal dose of venomous PLA2, L&K-NPs also inhibit hemolysis and confer a significant survival benefit. Furthermore, L&K-NPs show no obvious toxicity in mice. and the design provides a platform technology for a safe and effective anti-PLA2 approach.

Context-Dependence and the Development of Push-Pull Approaches for Integrated Management of Drosophila suzukii

Sustainable pest control requires a systems approach, based on a thorough ecological understanding of an agro-ecosystem. Such fundamental understanding provides a basis for developing strategies to manipulate the pest’s behaviour, distribution, and population dynamics, to be employed for crop protection. This review focuses on the fundamental knowledge required for the development of an effective push-pull approach. Push-pull is a strategy to repel a pest from a crop, while attracting it toward an external location. It often relies on infochemicals (e.g., pheromones or allelochemicals) that are relevant in the ecology of the pest insect and can be exploited as lure or repellent. Importantly, responsiveness of insects to infochemicals is dependent on both the insect’s internal physiological state and external environmental conditions. This context-dependency reflects the integration of cues from different sensory modalities, the effect of mating and/or feeding status, as well as diurnal or seasonal rhythms. Furthermore, when the costs of responding to an infochemical outweigh the benefits, resistance can rapidly evolve. Here, we argue that profound knowledge on context-dependence is important for the development and implementation of push-pull approaches. We illustrate this by discussing the relevant fundamental knowledge on the invasive pest species Drosophila suzukii as an example.

Laboratory and Field Evaluation of Host-Related Foraging Odor-Cue Combinations to Attract Drosophila suzukii (Diptera: Drosophilidae)

The invasive spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major pest of soft-skinned fruits. Since its introduction into North America and Europe, significant progress has been made in understanding the volatile cues used by this fly during food, oviposition site, and mate finding. Despite this progress, commercially available lures are non-selective. Here, we tested two Hanseniaspora uvarum (Niehaus) yeast compounds (isoamyl acetate and isobutyl acetate) and a leaf compound β-cyclocitral alone and in combination with a blend of four fermentation compounds ('Fermentation lure': acetic acid, ethanol, methionol, and acetoin) to improve D. suzukii attraction and selectivity. In laboratory assays, males and females were attracted to all seven individual compounds, although in electrophysiological assays, their antennae exhibited a dose-dependent response to only four of these compounds. In two-choice cage studies, the Fermentation lure was more attractive to D. suzukii than water controls, whereas β-cyclocitral and the mixture of isoamyl acetate and isobutyl acetate were not attractive in this larger-cage study. Moreover, adding the two-component H. uvarum compound blend to the Fermentation lure reduced D. suzukii attraction to the Fermentation blend. When these experiments were repeated in blueberry, raspberry, blackberry, and cherry orchards across several states in the United States over 2 yr, similar outcomes were observed: β-cyclocitral or the mixture of the H. uvarum blend did not improve the attractiveness of the Fermentation lure or its selectivity. This study demonstrates that cues from different sources may interfere with each other and reduce D. suzukii attraction to otherwise attractive odor combinations.

Effects of Trap Color and Shape on the Capture of Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae)

Eucryptorrhynchus scrobiculatus (Coleoptera:Curculionidae) is an important pest in China that specifically damages Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae). Trembler grid lamps and food attractant traps frequently were used to monitor and control E. scrobiculatus; however, the effect of these methods is poor in actual application. The purpose of this study was to develop a new monitoring method. Traps of seven colors and two shapes were compared with respect to the attraction of E. scrobiculatus adults, and a field trapping test was performed. We found that E. scrobiculatus adults were most sensitive to red (16.11 ± 7.72) and black traps (14.44 ± 8.07) and to tall vertical black shapes in the laboratory. In the field, red (70.50 ± 5.74) and black traps (60.75 ± 8.22) were most effective at catching E. scrobiculatus, and traps with color and attractant still were more attractive to E. scrobiculatus than traps with colors only. These results provide a reference for monitoring E. scrobiculatus adults.

Effect of Vegetable Oils as Phagostimulants in Adults of Dichroplus vittigerum (Orthoptera: Acrididae)

Several species of grasshoppers are attracted to vegetable oils. These oils have kairomonal properties mainly due to the presence of linolenic and linoleic fatty acids. This study aimed to determine whether the odors of canola, flax, and olive oils are attractive to Dichroplus vittigerum (Blanchard 1851) and if they induce preference and feeding. We conducted three bioassays to determine whether oil modifies attraction and feeding behavior of this grasshopper. We first determined the attraction of the oils using a wind tunnel, secondly evaluated phagostimulation produced by the oils, and finally performed preference tests comparing consumption of Taraxacum officinale (Weber ex F.H.Wigg. 1780, Asterales: Asteraceae) leaves treated with the oils versus control leaves. Even though all of the oils induced attraction, only flax oil acted as a phagostimulant. However, the oils did not determine the preference and did not increase feeding on leaves. We hypothesize that T. officinale leaves are inherently attractive and treatment with oils did not affect feeding on them. Our results provide a starting point to develop baits that can be used to attract and control these harmful insects, presenting flax oil as a potential bait for D. vittigerum since its odor was both attractive and led to increased feeding or phagostimulation. Future studies should test the effect of the oils on other plant species or at varying doses, under field conditions.

Electrophysiological and Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) Towards the Leaf Volatile β-cyclocitral and Selected Fruit-Ripening Volatiles

The spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is attracted to numerous volatile organic compounds (VOCs) emitted from several ripening, small fruit crops. However, the strawberry leaf terpenoid, β-cyclocitral, is reportedly very attractive to D. suzukii (but not to all Drosophila spp.). This suggests that leaf and fruit VOCs may be critical sources needed to further develop a more species-specific D. suzukii monitoring lure, or semiochemically based attract-and-kill systems. This study investigated the electrophysiological responses of male and female D. suzukii towards selected host fruit-ripening VOCs and β-cyclocitral, along with behavioral responses toward combined fruit VOCs with β-cyclocitral. Electroantennogram (EAG) results revealed a positive dose-response, for both sexes, as concentrations increased for all VOCs tested. For β-cyclocitral, hexyl acetate and methyl butyrate, the mean male EAG responses were significantly greater than the female responses at lower doses. In caged behavioral bioassays, only in the β-cyclocitral treatments were the mean number of flies captured (sexes combined) significantly greater than that captured in solvent (mineral oil) controls. Our study has demonstrated that while single fruit-based VOCs alone are not enough to cause a strong behavioral attraction by both male and female D. suzukii, the addition of β-cyclocitral did produce a significant attraction response from both sexes. In both bioassays, males had higher responses to β-cyclocitral than females, which suggest a greater sensitivity to this compound. Further studies are needed to ascertain the role β-cyclocitral may play in the development of a more species-specific D. suzukii monitoring lure.

The Behavioural Effects of Innovative Litter Developed to Attract Cats

Urination and/or defecation outside a designated location has been reported as the most common behavioural reason for surrendering a cat and comprises approximately 30% of cat intakes to shelters. The objective of this study was to determine whether cats would increase in-box elimination when provided a plant-based litter product with attractant (ATTRACT) compared to the same plant-based litter product without attractant (PLANT). Sixteen cats were split into two equal cohorts based on availability from the shelter and group-housed in an enriched room with eight identical litter boxes arranged in a circular pattern equidistant from each other. Following a two-week room acclimation and transition period from clay litter to PLANT litter, boxes were designated either PLANT or ATTRACT litter, balancing for cats' prior box location preferences. For 14 days following litter allocation, cat behaviours such as sniffing, digging, covering, urinating, and defecating were video recorded for 12 h daily. The cats urinated more often in the ATTRACT litter, suggesting that they preferred the ATTRACT litter for urination more than the PLANT litter (p < 0.05). The most significant differences observed were between genders, with males spending significantly more time sniffing and performing urination behaviours (p < 0.05). These results suggest that litter with an attractant may be more effective in eliciting usage for urination, as compared to a litter without the additive.

Sex Pheromone of the Invasive Mealybug Citrus Pest, Delottococcus aberiae (Hemiptera: Pseudococcidae). A New Monoterpenoid with a Necrodane Skeleton

Native to sub-Saharan Africa, Delottococcus aberiae De Lotto (Hemiptera: Pseudoccidae) is an invasive mealybug that has been recently reported in Europe, seriously damaging citrus production in eastern Spain. In this study, we isolated and determined the structure of the sex pheromone of D. aberiae, to provide a highly specific and effective lure for detecting, monitoring, and potentially controlling this pest. The volatile profile of D. aberiae virgin and mated females was studied by aeration and collection of effluvia in Porapak-Q. The resulting extracts were analyzed by gas chromatography coupled to mass spectrometry (GC-MS), revealing a candidate compound specific of virgin females. GC-MS and nuclear magnetic resonance spectroscopy data evidenced a new compound, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate, with an unusual β-necrodol skeleton. This compound was synthesized and shown to be attractive to male D. aberiae in both laboratory and field experiments. A GC analysis using an enantioselective stationary phase and polarimetry analyses of the synthetic enantiomers showed the natural compound emitted by virgin females to be the - enantiomer.

Isoeugenol, a More Attractive Male Lure for the Cue-Lure-Responsive Pest Fruit Fly Bactrocera curvipennis (Diptera: Tephritidae: Dacinae), and New Records of Species Responding to Zingerone in New Caledonia

Bactrocera curvipennis (Froggatt) is a polyphagous pest fruit fly endemic to New Caledonia that is weakly attracted to the male lure cue-lure (CL). Effective male lures are important for the monitoring and management of numerous pest species of Dacinae fruit flies. However, if a species is weakly responsive to these lures its detection and control is difficult. Recently in Oceania and Asia, more attractive male lures (isoeugenol, methyl-isoeugenol, dihydroeugenol, and zingerone) were identified for several weakly CL- and methyl eugenol (ME)-responsive species. To determine if these lures may be more attractive to B. curvipennis, we field tested them in comparison to CL and ME in New Caledonia. Bactrocera curvipennis catch with isoeugenol-baited traps (mean 20.3 ± 3.0) was 15 times greater than with CL (1.3 ± 0.8) and catch with dihydroeugenol (5.7 ± 1.6) was four times greater than with CL. This is the first record of B. curvipennis responding to these lures. It was also the only species that responded to isoeugenol in this study. Bactrocera fulvifacies (Perkins) (Diptera: Tephritidae), a rarely encountered species 'nonresponsive' to male lures, was attracted to zingerone with its trap catch (2,574 flies) approaching that of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) at CL (2,724 flies). Another nonresponsive species, Dacus aneuvittatus (Drew) (Diptera: Tephritidae), was also trapped by zingerone-baited traps. This is the first record of these species responding to a male lure. The significantly greater response of B. curvipennis to isoeugenol would make it a considerably more effective attractant for use in surveillance and control programs.

Raspberry Ketone Trifluoroacetate Trapping of Zeugodacus cucurbitae (Diptera: Tephritidae)in Hawaii

Melon fly, Zeugodacus cucurbitae (Coquillett), is a serious pest of tropical horticulture, causing damage to cucurbits, other fruiting vegetables, and certain tree fruits. The deployment of male lures comprises an important component of several detection and control strategies for this pest, with the main male attractant currently in use being cuelure (CL). A novel fluorinated analog of CL, raspberry ketone trifluoroacetate (RKTA), has been developed for the control of Bactrocera tryoni, a related pest; here, we test this compound for attraction to Z. cucurbitae. In outdoor screen cage testing, observations showed both more flies on filter papers, and a higher percentage of flies feeding, on papers treated with RKTA than on those with CL or melolure (ML). Field trapping with both yellow sticky traps and bucket traps found that RKTA captured more flies during the first 6 h of trapping than CL, while trap captures in the subsequent 18 h did not differ between the two lures. When comparing combined 24 h trap captures, yellow sticky traps containing RKTA captured more flies than those with CL, while bucket trap captures did not vary by lure. Analysis of lures weathered on filter paper found that nearly all applied RKTA hydrolyzed to RK within 6 h. Fine-scale melon fly behaviors digitally recorded in the field showed median resting distances from the lure of responding flies were shorter for RKTA than for CL. This study demonstrates the inherent attractiveness of RKTA while also highlighting the instability of this compound due to hydrolysis.