Journal of Chemical Ecology最新文献

In this study, the volatile compounds found in lemon trees infested and uninfested with Planococcus citri (Risso) (Hemiptera: Pseudococcidae) were investigated. In addition, the interest of the predator Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) and the parasitoid Leptomastix dactylopii (Hymenoptera: Encyrtidae) in lemon trees infested and uninfested with P. citri and some volatile compounds was investigated. According to the results obtained, most of the volatile compounds obtained from mealybug-infested lemon trees showed changes compared to healthy lemon trees. Since volatile compounds play an important role in attracting pests and natural enemies, linalyl acetate was selected as the compound showing the highest amount of changes, and its attractiveness to predators and parasitoids was tested first in the laboratory using a Y-olfactometer and then in a lemon orchard in combination with a yellow sticky trap. In the olfactometer tests, linalyl acetate was found to be attractive to predators and parasitoids. In field studies, the number of predators and parasitoids increased in traps containing linalyl acetate compared to traps containing only paraffin oil. Our results suggest that linalyl acetate may play a role in attracting both predators and parasitoids and can be combined with these natural enemies in biological control studies.

Hymenoscyphus fraxineus is an invasive pathogen native to East Asia, responsible for the widespread mortality of European ash (Fraxinus excelsior) throughout Europe. Asian ash species, which co-evolved with H. fraxineus, are considered more tolerant than European ash. However, within European ash populations, a small proportion of genotypes show low susceptibility to the pathogen. This study sought to characterize the underlying defence mechanisms to H. fraxineus by performing untargeted constitutive metabolomics profiling of phloem and leaf tissue of from thirteen F. excelsior genotypes (nine tolerant and four susceptible) and five genotypes representing three Asian ash species (F. mandshurica, F. platypoda, and F. chinensis). Here we report 57 and 36 compounds associated with lower or higher disease susceptibility, from phloem and leaf tissue, respectively. Flavonoids and coumarins were the main classes of detected compounds. In particular, quercitrin and fraxetin exhibited greater variation among the groups. In phloem tissue, quercitrin and fraxetin were more abundant in tolerant than in susceptible European ash and, lowest in Asian ash species. In leaves, however, quercitrin was highest in Asian ash, followed by tolerant and then susceptible European ash. Other flavonoids, coumarins, and iridoid glycosides also showed variation among groups, with stronger differences in phloem than in leaf tissue. Overall, this study advances our understanding of metabolite composition in Fraxinus species with different co-evolutionary histories and susceptibility to H. fraxineus and demonstrates the potential of untargeted metabolomics for investigating defence-related mechanisms in plant-pathogen interactions.

Male attractants are widely used to detect and control Tephritidae pest species. When naturally ingested by males, these compounds modify the sex pheromone composition, enhancing male attractiveness to females and thereby increasing individual reproductive success. The evolutionary origin of this sexual selection is uncertain, as male attractants differ across species. To investigate this, we compared the olfactory responses of males from nine Tephritidae species-Bactrocera dorsalis, Bactrocera zonata, Ceratitis capitata, Ceratitis catoirii, Ceratitis quilicii, Dacus ciliatus, Dacus demmerezi, Neoceratitis cyanescens, and Zeugodacus cucurbitae-to compounds known to attract males in at least one species within the family. Using a six-way olfactometer and a high-throughput Flywalk behavioural assay, we found species-specific attraction profiles. Species were globally separated into methyl eugenol responders, cuelure responders, and non-responders, with small variations observed within the groups. Using three-point electroantennography and electropalpography, we found most compounds elicited peripheral responses in males across all species, with weak connection to behavioural preferences. Consistently, peripheral responses did not predict behavioural groups. Notably, among the two species attracted to methyl eugenol, only B. zonata showed a stronger antennal response to this compound than other species, whereas cuelure peripheral responses were weak across all species. Our findings suggest that male attraction in Tephritidae may have evolved through pre-existing signal reinterpretation in the central nervous system, leading to novel behavioural outputs. Overall, this study provides valuable behavioural and electrophysiological data for understanding olfactory mechanisms underlying responses to semiochemicals used in pest management.

Repellent and electrophysiological activity of catnip (Nepeta cataria L.) essential oils (EOs) and the main chemical components were evaluated against nymphs and adult female Ixodes scapularis ticks. Horizontal repellency bioassays were conducted on three selected catnip essential oils, and only nepetalactone-rich catnip oil exerted the strongest repellency. Five varieties of catnip essential oils (EOs) were analyzed using gas chromatography-mass spectrometry (GC-MS) to determine their chemical compositions. Among them, nepetalactone isomers (trans-cis isomer 76.6 ± 0.3% and cis-trans isomer 16.9 ± 0.4% relative overall abundance) were detected in only one EO variety. Other major compounds detected in the other EO varieties were α-pinene and menthone. To further assess the role of nepetalactone, isomers were isolated by liquid chromatography, and the cis-trans isomer was further prepared through an epimerization reaction of the trans-cis isomer. The electrophysiological response of adult tick females to a known attractant and host volatile (i.e., butyric acid), pre- and post-exposure to catnip EO and main component nepetalactone isomers, was recorded. Exposure was assessed using a fumigation assay, which revealed that pre-exposure to catnip EO and individual nepetalactone isomers significantly reduced the tick response to butyric acid. Horizontal repellency bioassays were conducted using the two nepetalactones, and it was found that the cis-trans isomer was mainly responsible for the observed activity by repelling 84.0 ± 7.5% of ticks after 2 hours. These results highlight the importance of chemical compositions of complex mixtures (such as EO) and the presence of specific compounds and isomers in eliciting the repellent effect in ticks.

Flowering plants serve as a valuable source of nectar, which supports the survival and reproductive success of flower-associated insects, including adult parasitoids. Fermentation by nectar-inhabiting microbes can alter nectar chemistry, which in turn, could affect the performance of nectar-feeding parasitoids. Although there is growing evidence on how yeasts and bacteria influence flower-visiting insects, the potential role of other microbial taxa that can colonize nectar has been largely neglected. In this study, we tested the hypothesis that filamentous fungi isolated from the nectar of buckwheat, Fagopyrum esculentum, affect nectar chemistry with cascading effects for the longevity of insect parasitoids. As model organisms, we used Trissolcus basalis and Ooencyrtus telenomicida, two co-occurring egg parasitoids of the southern green stink bug, Nezara viridula. Laboratory bioassays showed that the longevity of T. basalis was reduced when wasps were fed on synthetic nectar fermented by Cladosporium sp. SAAF 22.2.12 and Cladosporium sp. SAAF 22.3.29, compared with wasps that fed on non-fermented synthetic nectar. On the contrary, no effects of fermentation by nectar-inhabiting fungi were reported in terms of longevity for O. telenomicida. Chemical analyses revealed that nectar fermentation by filamentous fungi substantially increased the chemical diversity of the nectar medium, with a total of 12 sugars and sugar alcohols detected in the fermented products of the different fungal strains, although in varying proportions. Altogether, these findings highlight the potential of neglected microbial taxa to affect nectar chemistry and longevity of adult parasitoids, broadening our understanding of plant-microbe-insect interactions.

While herbivore-induced plant volatiles are well-established cues that guide natural enemies to herbivores in ecosystems, microbe-induced plant volatiles have recently gained attention as promising tools for achieving similar outcomes. However, how nocturnal predators respond to volatile cues induced by herbivory and/or endophytic fungal remains poorly understood, particularly in systems where the predator and plant do not share a tightly co-evolved or highly specialized relationship. To explore this, we investigated whether Spodoptera frugiperda infestation and Metarhizium robertsii endophytic colonization in sugarcane plants could enhance the olfactory attraction of the nocturnal earwig predator Doru luteipes by modifying nocturnal volatile emissions and altering endogenous levels of jasmonic acid and salicylic acid. Unexpectedly, the changes in volatile emissions and phytohormone levels induced by herbivory and microbial colonization led to a reduced attraction of the predator compared with undamaged control plants and with the no-plant control. These findings highlight the complexity of D. luteipes' responses to induced indirect defenses in sugarcane, suggesting that such strategies may not consistently enhance the recruitment of natural enemies.

Trichoderma species are widely used as root-colonizing biocontrol agents that enhance plant resistance to biotic and abiotic stresses while promoting growth. These fungi produce diverse volatile and non-volatile metabolites that mediate interactions with plants. Trichoderma can influence both direct and indirect plant defenses, including the release of herbivore-induced plant volatiles (HIPVs) that attract natural enemies of herbivores. In this study, we examined the effects of T. virens and its vir4 gene (regulating terpenoid synthesis) knockout-mutant on maize (Zea mays), the herbivore Helicoverpa armigera, and its predator Macrolophus pygmaeus. Previous research has shown that T. virens differentially modulates maize root gene expression and specialized metabolite concentrations. Here, we found that caterpillars feeding on maize seedlings colonized by wild-type T. virens gained significantly less weight than those feeding on maize colonized by the vir4 knockout mutant or uncolonized plants, suggesting that the vir4 gene cluster contributes to herbivore resistance. Although fungal colonization led to moderate changes in HIPV composition, total volatile emissions remained unchanged. In Y-tube assays, M. pygmaeus preferred caterpillar-infested maize over healthy plants, but fungal colonization did not significantly affect predator behavior. Our findings demonstrate that T. virens enhances direct plant defense against herbivores while maintaining indirect defense through a mechanism regulated by terpenoid synthesis depending on vir4 gene. Further research is needed to elucidate the metabolic changes in maize induced by T. virens that contribute to reduced herbivore performance.

Volatile organic compounds (VOCs) emitted by flowers and aquatic microorganisms influence mosquito behavior, but the role of water- and nectar-dwelling yeasts remains underexplored. In Aedes albopictus, we characterized yeast communities from visited and non-visited flowers, and from colonized and non-colonized breeding-site waters in urban community gardens. Mint flowers were preferentially visited, and the yeasts Metschnikowia reukaufii and Aureobasidium pullulans, present at higher densities in this plant, strongly attracted adult males and females, respectively. GC-MS analysis showed that M. reukaufii emitted a greater diversity of VOCs than A. pullulans, including specific compounds (3-methylbutyl acetate, 2-methylbutyl acetate, ethyl acetate, and ethyl hexanoate) and higher concentrations of shared ones (3-methylbutan-1-ol, ethanol, 2-methylbutan-1-ol, 2-methylpropan-1-ol). For aquatic yeasts, Rhodotorula mucilaginosa and Cystobasidium slooffiae attracted gravid females, whereas Hanseniaspora uvarum, Torulaspora delbrueckii, Pichia kluyveri, and Papiliotrema laurentii repelled them, when present at higher cell densities. Repellent yeasts emitted a greater VOC diversity, including specific compounds such as ethanol, 3-methylbutyl acetate, ethyl acetate, pentyl propanoate, and ethyl propanoate, and higher concentrations of two shared compounds with attractive yeasts (3-methylbutan-1-ol, 2-methylbutan-1-ol). Further studies are needed to identify which compounds and concentrations mediate these effects and whether nectar-dwelling yeast attraction is linked to nectar feeding and mosquito fitness.

Aphis craccivora (AC) and Aphis gossypii (AG) are serious pests of Lablab purpureus subsp. bengalensis. Binodoxys indicus is a parasitoid of both aphids. Thus, it is interesting to observe the behavioral responses of both aphids and the parasitoid to volatiles of undamaged (UD), insect-damaged (ID, plants infested by each aphid for 48-120 h) and jasmonic acid (JA)-treated plants. In olfactometer bioassays, aphids preferred the volatiles from UD and ID plants, whereas the parasitoid preferred volatiles from ID plants. Aphids and the parasitoid preferred volatiles of ID 120 h plants over ID 48 h plants. Aphids and the parasitoid did not prefer the volatiles of JA-treated plants. GC-MS analysis of volatiles from UD, AC-infested, AG-infested and JA-treated plants demonstrated the presence of 23, 28, 29 and 27 compounds, respectively. To identify key volatile compounds responsible for the behavioral responses of aphids and the parasitoid, all individual synthetic compounds for each treatment were tested in olfactometer bioassays. AC and AG showed attraction to eight and seven individual compounds, respectively, resembling 120 h conspecific-damaged plants. The parasitoid, B. indicus, showed attraction to five and four individual compounds resembling 120 h AC- and AG-infested plants, respectively. The above eight and seven compound blends could be used as lures in baited traps to capture both aphids in Lablab fields, whereas the above five and four compound blends could be applied to intensify the foraging behavior of B. indicus during early infestation of these aphids in Lablab plants in integrated pest management strategies.

The tortoise beetle Stolas conspersa (Coleoptera: Chrysomelidae, Cassidinae) exhibits strong host specialization on Mikania spp. (Asteraceae), yet field and laboratory observations reveal contrasting patterns. In natural habitats, beetles predominantly aggregate on Mikania salviifolia, whereas laboratory assays indicate a clear preference for an as-yet-unidentified species, Mikania sp. To resolve this apparent paradox, we investigated this system by combining chemical analyses, behavioral bioassays, and electrophysiological recordings. Analysis of essential oil profiles revealed distinct chemical signatures: M. sp. was dominated by monoterpenes (87.9%), particularly α-phellandrene, whereas M. salviifolia produced exclusively sesquiterpenes, with β-elemene as the main component. In Y-tube assays, females exhibited strong attraction and preference to M. sp. volatiles and showed robust antennal responses to the complete oil blend, but they did not respond to the synthetic versions of the major individual volatile compounds, suggesting that recognition relies on minor components or the full volatile mixture. Males showed no responses. Field surveys revealed that both species co-occur in the same localities. However, M. sp. is subject to mechanical trimming and disturbance by human activities, whereas M. salviifolia remains largely undisturbed in its microhabitat. These conditions suggest that females balance an innate preference for monoterpene-rich blends with ecological flexibility, exploiting M. salviifolia when habitat stability ensures reliable host availability despite the lower chemical attractiveness of its sesquiterpenes. This system illustrates how insects may adjust host use in response to local habitat context. Overall, our study demonstrates that host choice in S. conspersa is shaped by the interplay between sensory specialization and environmental context, highlighting the role of disturbance in modulating insect-plant interactions.