Journal of Chemical Ecology最新文献

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.

Jasmonic acid (JA) is a key regulator of plant development and plant defence. Seed priming with JA and methyl jasmonate (MeJA) has been proposed as an ecologically-sound and cost-effective method to improve crop protection. While several studies have shown their efficacy in boosting production of non-volatile defensive compounds, the effects of seed treatments on volatile organic compounds (VOCs) are largely unknown. Using broccoli and Plutella xylostella as a model system, we tested how two pre-sowing MeJA treatments (0.1 and 0.01 mM MeJA) impact constitutive and herbivore-induced VOC emissions, net photosynthesis (A) and stomatal conductance (Gs). The results showed that at 0.1 mM MeJA, the treatment significantly increased the emissions of (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate. In contrast, the emission of (E, E)-α-farnesene was significantly reduced in MeJA-seed treated plants, compared to untreated plants. At 0.01 mM MeJA, no effect of the MeJA treatment on the whole blend was observed, although there was an effect of MeJA on (E, E)-α-farnesene, which decreased. However, at this concentration plants were primed for a greater VOC response upon herbivore damage. Although A and Gs tended to increase in plants grown from seeds treated with 0.1 mM MeJA, no significant changes were observed for either of the concentrations. The treatment did not significantly affect leaf consumption or oviposition, even though more eggs were laid on the MeJA treated plants compared to the control, at the concentration of 0.1 mM MeJA. Together, the results showed that MeJA can alter the VOC emissions, and suggest that, 0.01 mM MeJA can prime herbivore-induced VOCs, without promoting oviposition of the pest.

The domestication of crops leads to profound changes on plant phenotypes, yet its effects on floral traits mediating plant-pollinator interactions remain poorly understood. Floral volatile organic compounds (VOCs) play a crucial role in pollinator attraction by signaling the presence and quality of available floral resources. Here, we characterize VOC composition in Cucurbita, a genus containing multiple wild and domesticated species, to investigate how domestication affects floral volatiles. Then, we combined electrophysiology, blue vane trap field assays and pollinator visitation experiments to assess how the squash specialist pollinator, Xenoglossa pruinosa, responded to existing VOCs across different wild and domesticated plant species. Our results reveal significant compound losses within domesticated species blends. Combined gas chromatography-electroantennography (GC-EAG) identified ten electrophysiologically active compounds across wild and domesticated squash VOCs. Field assays assessing bee attraction to individual antennally active compounds using modified blue vane traps with compound lures identified 1,4-dimethoxybenzene (a dominant volatile in domesticated squash blends) as an attractant for bees in isolation. We also found significant associations between bee visitation (assessed as floral approaches and nectaring behaviors) and increased emissions of 1,4-dimethoxybenzene, dihydro-β-ionone, and (E)-nerolidol as well as reduced emissions of linalool and methyl salicylate. Our findings provide novel insights into the chemical ecology of crop-pollinator interactions, demonstrating that domestication can reshape plant-pollinator communication mechanisms.

The larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), is a major invasive pest of stored grains with the potential to expand its range across North America. While primarily associated with stored grains, this species could exploit non-grain hosts that facilitate survival and dispersal across broader geographic ranges. Previous research has shown that acorns can be a suitable food for a related stored product bostrichid. Here, we assessed the odor preference of P. truncatus for acorns from black oak (Quercus velutina), red oak (Quercus rubra), and bur oak (Quercus macrocarpa) compared to maize and wheat, and analyzed their volatile organic compound (VOC) profiles. Further, we measured P. truncatus feeding and reproduction on these acorns. Results demonstrated that P. truncatus responded to volatiles of each acorn species but responded most positively to bur oak acorns. Interestingly, bur oak acorns were also more attractive than maize, its main host grain. VOC profiles showed that 3-hepten-2-one and 2-(5-methyl-furan-2-yl)-propionaldehyde were detected only in bur oak acorns, which may contribute to odor preference. Prostephanus truncatus also preferred to feed on bur oak acorns over other oak species. Among the oak species tested, F₁ progeny were detected only in bur oak acorns. These results suggest that P. truncatus exhibits host-use flexibility that enables it to utilize acorns in the absence of grains, highlighting the potential risk of landscape-level invasion by this pest in North America.

The release of volatile organic compounds (VOCs) plays a crucial role in plant-to-plant and plant-to-arthropod communication. Each blend of VOCs released carries a specific meaning for the receiving party and the stimulus that triggers a response. One such stimulus, vibrations from insect feeding, has been shown to elicit chemical defense responses in rosettes of Arabidopsis thaliana. In this study, we measured herbivore-induced plant volatiles (HIPVs) in response to 4 h of insect feeding vibrations using solid-phase microextraction (SPME) fibers in small collection chambers and a miniature Gas Chromatography-Flame Ionization Detection (GC-FID) system. The concentrations of Eugenol, β-caryophyllene, β-ionone, and MeSA increased within 4 h in response to insect feeding vibrations, indicating that these HIPVs are a sensitive response to this initial signal of herbivore attack.

Many herbivorous species are considered specialists that feed not only on specific plant taxa, but also on certain organs. Numerous species feed on leaves (folivory), while supplementary feeding on flowers (florivory) or switching in diets is less commonly considered. We used the mustard leaf beetle, Phaedon cochleariae, known to feed on leaves of Brassicaceae, such as Nasturtium officinale, to test whether it also accepts flowers, whether different stages show different preferences for certain plant organs, how the glucosinolate contents of the plant parts differ and how individuals develop on either single or mixed diet. In preference tests, larvae and adult males did not differentiate between young and old leaves or leaves versus flowers, but rarely accepted fruits. Adult females preferred young over old leaves and leaves over flowers, while they did also accept fruits. Total glucosinolate concentrations were higher in young leaves and flowers than in old leaves and fruits. In development assays with four different groups of diets, larvae that were exclusively fed on leaves or switched to flowers over the larval development developed faster than those only fed on flowers. However, exclusive feeding on leaves led overall to the highest fertility, while individuals fed exclusively on flowers showed by trend the lowest survival. Since P. cochleariae can apparently also feed and develop on flowers, a switch to this organ may be beneficial if leaves turn senescent or to exploit a competition- or enemy-free niche. Partial florivory amongst species considered to be folivores may be more widespread than assumed.

The effects of exogenous application of methyl jasmonate (MeJa), a ubiquitous hormonal elicitor of plant defense, was tested for the ability to upregulate monoterpenes and induce production of traumatic resin ducts in Engelmann spruce (Picea engelmannii). MeJa treatments were applied a single time at one of three concentrations (1-, 10-, and 100-mM) and phloem monoterpene responses were evaluated during the same growing season and one year post-treatment. MeJa application affected monoterpene profiles in a time-specific manner. Total monoterpene concentrations were unaffected by MeJa in the year of application (P = 0.692) but concentrations of several monoterpenes including γ-terpinene, terpinolene, linalool were elevated for trees receiving the 100 mM application, indicating treatment affected monoterpene compositions. Both γ-terpinene (P = 0.008) and terpinolene (P < 0.001) were elevated within one week of application but later declined to control levels, whereas linalool was elevated two weeks after application and remained higher than control for the remainder of the growing season (P < 0.001). Evaluation of traumatic resin duct formation the following year revealed higher frequencies of traumatic resin ducts in growth increments for trees receiving 10- and 100-mM treatments. Occurrence of traumatic resin ducts moderately predicted variation in total monoterpene concentration the year following treatment (P = 0.069). Trees forming resin ducts bisecting between 20 and 90% of the previous year's growth increment had ~ 39% higher mean phloem monoterpene concentrations than trees with fewer ducts or those that were completely occluded by ducts. These results indicate that exogenous MeJa application alters monoterpene profiles shortly following application and may have latent, resin duct-mediated effects on total monoterpene concentrations. Potential ecological impacts are discussed.

The role of microbial communities in aphid honeydew in shaping multitrophic interactions remains uncertain, while bacterial diversity and its variation among aphid species and ageing are still underexplored. This study investigated variations in bacterial community structure and VOC profiles of honeydew between two aphid species (Aphis fabae, Acyrthosiphon pisum), across time from fresh to 72-hour aged. We also assessed the behavioral responses of a natural enemy of aphids, the hoverfly Episyrphus balteatus, to different honeydew combinations. Aphis fabae honeydew harbored a more diverse bacterial taxonomic richness than A. pisum, including a significant shift in bacterial community composition over time that also extended to the semiochemical profiles. Further, 24-hour-aged honeydew from A. fabae emitted a higher concentration of volatile compounds than A. pisum. We assessed E. balteatus preferences for aged honeydew from both aphid species using wind tunnel assays, revealing a strong attraction to 48-hour-old A. pisum honeydew resulting in higher egg-laying activity. These findings underscore the role of microbial succession in aphid honeydew in shaping multitrophic interactions, suggesting potential biocontrol strategies by modulating microbial influences on aphidophagous beneficial behavior.