Journal of Chemical Ecology最新文献

Glucosinolates (GS) are sulfur-containing compounds that serve as a deterrentto herbivores, though are tolerated by some specialized insects. The correlation of GS with floral traits such as colour and scent might represent a signaling of defense status, a pattern rarely recorded in natural populations. We used Raphanus raphanistrum to discover GS signaling patterns and their effects on plant fitness. We recorded fitness, floral colour, GS, and floral Volatile Organic Compounds (fVOCs) from five natural populations. We then tested correlations among traits at the species level and at the population level. Plant fitness was not correlated with any of the GS and fVOCs analysed. At the species level, flower colour was correlated with GS levels in leaves indicating that there might be visual signaling of defense status, while there was a weak correlation between minor GS and fVOCs. However, at the population level, we found multiple and discordant significant correlations, mainly negative, between GS and fVOCs. Our study indicates that signaling channels used by R. raphanistrum to advertise its chemical defense are complex and variable among populations suggesting that they can be shaped by biotic networks of pollinators and herbivores varying in space.

Corn plants are susceptible to infection by fungi such as Aspergillus flavus that have the potential to produce several types of mycotoxins, one of the most potent ones known to exist is aflatoxin. Since aflatoxin contaminated corn must be destroyed, causing annual monetary losses in billions of dollars, it would be helpful to detect the presence of aflatoxin producing fungi at pre-harvest and pre-planting stages. To this end, it may be possible to capture volatile organic compounds these fungi produce while overwintering in the soil or while infecting corn plants. In this study, we acquired A. flavus VOCs from conidia and sclerotia, while residing in the soil environment. We concluded that soilborne conidia and sclerotia have specific VOC signatures, and sclerotia tend to emit specific VOCs at greater abundance compared to soilborne conidia or fungus-free soil. These sclerotium-specific VOCs include geranyl acetone, caryophyllene compounds, and methanone. Bioassays using toxin producing and non-producing fungi showed that β-caryophyllene increased spore concentration, and both β-caryophyllene and caryophyllene oxide were able to modulate aerial hyphae, sclerotia production and decrease aflatoxin, cyclopiazonic acid and ditryptophenaline production in A. flavus strains. Our results show insights into the ecological roles that β-caryophyllene and caryophyllene oxide have over A. flavus' development and metabolism, although their effect on multitrophic interactions among corn, fungi and other potential organisms are still not fully understood. These VOCs could serve as an agricultural surveillance management system that enables early mitigation of aflatoxin producing fungi outbreaks in the field.

Saponins are structurally diverse bioactive metabolites found in more than 100 plant families and are synthesized by plants as protection against insects, fungi, and other organisms. The mode of action is related to their interference with membranes, and particularly the membrane sterols. As membrane sterol composition varies across kingdoms and species, species-specific differences in toxicity may therefore be expected. The aim of this study was to elucidate the structure-activity relationships of different saponins across four different organisms (Daphnia magna, Enchytraeus crypticus, Saccharomyces cerevisiae, Raphidocelis subcapitata) representing three eukaryotic kingdoms of life using either immobility tests or growth inhibition assays. We hypothesized that monodesmosidic saponins are more bioactive due to higher amphiphilicity/polarity and that species susceptibility depends on sterol composition, with organisms containing plant sterols being less susceptible than those with animal or fungal sterols. The hypothesis was supported for monodesmosidic saponins, as α-hederin and hederacolchiside A1 exhibited significant cytotoxicity (EC50 values ranging from 8.7 to 36.9 and 2.0- 68.9 mg/L, respectively, for the different organisms), whereas bidesmosidic saponins such as hederacoside C and ginsenoside-Ro were inactive at concentrations up to 100 mg/L. The aglycone backbone and sugar moiety composition, however, also play critical roles, with simpler, linear saccharide chains leading to increased toxicity. C-23 hydroxylation has been shown to enhance mortality against insects; however, its absence did not affect the ability of hederacolchiside A1 to exhibit toxic properties. Additionally, species-specific sensitivities varied, with the crustacean D. magna being the most sensitive species, followed by the anelid worm E. crypticus, yeast S. cerevisiae, and the least-sensitive was, as hypothesized, the algae R. subcapitata. These insights contribute to a deeper understanding of saponin structure-activity relationships and open new avenues for the targeted development of saponin-based applications in agriculture, medicine, and biotechnology.

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.