Journal of Chemical Ecology最新文献

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.

Pharmacophagy is a fascinating phenomenon, where animals take up specialized plant metabolites unrelated to nutrition, but with benefits for, for example, defense and mating. Adults of the turnip sawfly Athalia rosae engage in pharmacophagy of neo-clerodane diterpenoids (clerodanoids) from the bugleweed Ajuga reptans, but can also take up metabolites sequestered from the plant and modified from conspecifics. Here, we investigated the perception of odors associated with pharmacophagy from long and close distances in bioassays, using leaves and washes of surface compounds, mainly cuticular hydrocarbons, from female and male adults of different pharmacophagy treatments. Extracts were analyzed by GC-MS to test whether the treatment affected the cuticular surface composition. We hypothesized that sawflies perceive compounds related to pharmacophagy at close distances, that sexes differ in surface compound profiles, and that contact with A. reptans leaves or previously A. reptans-exposed conspecifics alters the cuticular hydrocarbon composition. Our results demonstrate that sawflies indeed perceive both plant leaves and surface washes from previously A. reptans-exposed conspecifics at close distance. We characterized the major cuticular hydrocarbons of A. rosae and uncovered sexual dimorphism in surface compound abundance, but found no pharmacophagy-induced changes in the surface compound composition. We discuss that other compounds than cuticular hydrocarbons are likely involved in the observed effects. Our research provides insights into how specialized plant metabolites may drive the evolution of the insect sensory behavior and into the complexity of insect chemical communication.

Plant volatile organic compounds (VOCs) constitute part of the signal transmitted between plants, serving as defence molecules that repel plant pests or attract their natural enemies. Insect-associated bacteria are important factors influencing many aspects of plant-insect interactions. In this study, we have undertaken to evaluate the impact of the insect-associated bacteria on the abundance and the content of VOCs emitted from wheat plants damaged by important cereal pest - cereal leaf beetle (CLB, Oulema melanopus), in both larval and adult stages. We assumed that CLB-associated bacteria, as an additional factor, may cause different and higher VOC emissions from plants attacked by insects. VOCs were collected by solid-phase microextraction and analyzed with comprehensive two-dimensional gas chromatography-mass spectrometry. We revealed that CLB-associated bacteria contribute to both the increased number and total peak area of VOCs emitted by plants exposed to CLB, particularly those classified as hydrocarbons, benzenoids, esters, and lactones. This effect is especially pronounced in plants damaged by larvae. Our findings demonstrate that physical damage alone may be sufficient to trigger the release of certain volatiles from plant tissues, but CLB feeding in the presence of its associated bacteria leads to a higher quantity and greater diversity of VOCs emissions.

Herbivory by mites often activates both jasmonate and salicylate signaling pathways in plants. While the role of jasmonic acid (JA) pathway in inducing plant defenses against mites is well established, the contribution of salicylic acid (SA) remains under debate. In previous studies, we found that herbivory by the mite Oligonychus ilicis (McGregor) (Acari: Tetranychidae) triggered the accumulation of both SA and JA, but increased plants susceptibility to subsequent herbivores. Here, we investigated the relative importance of SA and JA signaling pathways in coffee resistance to O. ilicis by applying methyl jasmonate (MeJA) and methyl salicylate (MeSA) as elicitors. To address this question, we combined behavioral assays (host selection and performance) with chemical analyses to attempt to identify and quantify secondary metabolites in plants treated with two concentrations of the elicitors (1.5 mM and 3.0 mM). Treatment with MeSA at 3.0 mM increased mite attraction but did not affect their performance. In contrast, treatment with MeJA at 3.0 mM reduced mite performance without altering mite preference, confirming the defensive role of the JA pathway. Levels of total phenolic compounds were not affected, but target analyses revealed that some phenolics were up-regulated by the elicitor treatments, such as syringic acid and coumaric acids in MeSA-treated plants and o-coumaric acid in MeJA-treated plants. By demonstrating the contrasting effects of MeJA and MeSA on the responses of coffee plants, our study extends the understanding of phytohormone-mediated defenses, providing guidance for sustainable pest management and deepening our comprehension of arthropod-plant interactions.

Beetles belonging to the Montella genus play a crucial role as pollinators for orchids. However, in Bahia state, Brazil, Montella sp. has been reported as a pest affecting Vanilla planifolia plantations, a highly economically valuable crop due to its status as the primary natural source of vanillin. Given the need for sustainable pest management strategies, this study aimed to identify the species' aggregation pheromone as a potential tool for monitoring and control. Through chromatographic analysis of volatiles released by males and females, two male-specific compounds were identified believed to be the species' aggregation pheromone based on behavioral experiments. The combination of analytical data and synthesis of standards allowed the identification of the main male-released semiochemical as the (10E,12Z)-hexadeca-10,12-dien-1-yl acetate (bombykyl acetate). Additionally, the minor compound (10E, 12Z)-hexadeca-10,12-dien-1-ol (bombykol), was also identified. Strikingly, these compounds are well-known lepidopteran pheromones, revealing a surprising trans-taxonomic convergence in chemical communication. To confirm the behavioral activity of these compounds in a weevil, Y-tube olfactometer assays were performed. Synthetic bombykyl acetate demonstrated strong attractivity for both sexes, confirming its role as the major aggregation-sex pheromone. This finding not only provides a foundation for the direct implementation of pheromone-based control methods but also challenges phylogenetic assumptions in chemical ecology.

By releasing volatile organic compounds (VOCs), French marigold and basil have been shown in the laboratory to disrupt the fecundity of the green peach aphid, Myzus persicae. Thus, they can be potential companion plants (CP) for target crops. To determine whether, fluctuating environment may impair their efficacy, three runs were carried out successively from March to June, during which we monitored the VOC emissions and the aphid population dynamics on pepper plants interplanted in different tunnels with basil, French marigold or pepper plants only. The presence of basil significantly decreased the daily fecundity and the intrinsic rate of natural increase of the M. persicae population, increasing the doubling time of the population, French marigold was less efficient. When expressed per degree days, basil and to a lesser extend French marigold significantly reduced aphid fecundity whatever the run, despite the fact that their VOCs blend emission differed. The volume of VOCs emission from CPs changed between runs, during the run, and at a daily scale. Most VOC emissions were significantly correlated with temperature over a 24 h VOC sampling period. These data support the hypothesis that the effectiveness of the olfactory message delivered by CPs can accommodate a variable production volume or composition. The involvement of a particular VOC or mixture of VOCs is difficult to establish, although the presence of (E)-β-farnesene (which could have a direct repellent effect on aphid) or eugenol (which could mediate plant-plant interaction and reduce pepper plant suitability) may be highlighted. This study confirms the efficacy of interplanting basil with pepper in tunnels to reduce M. persicae fecundity despite fluctuating temperatures that modify basil volatile blend.