Journal of Chemical Ecology最新文献

Flowering plants attract pollinators via traits such as floral scent and morphology, which are often influenced by other interactions like herbivory. However, the effects of herbivory on floral traits may not be consistent across traits, resulting in changed relationships between multimodal traits that could alter pollinator perception. We investigated how herbivory affects floral scent and morphology, and alters correlations between signaling traits. In a natural community, we simulated herbivory seven days before flowering on eight Asclepias syriaca (common milkweed) plants by removing half of their foliar tissue and applying a jasmonic acid solution; eight additional plants received a control spray with solvent only and no damage. After treatments, we collected floral volatile organic compound (VOC) emissions (i.e., scent) and measured five floral morphological traits on all plants. We found that simulated herbivory significantly altered VOC composition. Additionally, herbivory increased flower diameter and hood width while decreasing hood height, but had no effect on inflorescence size, measured as flower number or dry mass. Notably, we found that simulated herbivory led to significantly stronger correlations in floral traits, including both flower morphology-VOC correlations and VOC-VOC correlations. This study demonstrates that herbivory induces changes in floral morphological traits and VOC emissions and increases correlations between floral traits. These findings highlight how herbivory can interfere with the floral traits that plants use to signal their pollination partners.

Lycorma delicatula is a polyphagous phloem feeder, which is spreading rapidly in the U.S., and is a major threat to grapes, hops, and ornamentals. Among its hosts, L. delicatula prefers Ailanthus altissima, an invasive tree from which it sequesters toxins, including several quassinoid compounds. We tested how these defenses affected predation by birds of nymphal and adult L. delicatula. Freeze-killed nymphs of each instar were reared with or without access to A. altissima and placed into cups on top of nest boxes occupied by house wrens (Troglodytes aedon). House wrens ate or fed their chicks a greater proportion of L. delicatula nymphs that had not had access to A. altissima than the nymphs that had access to this host plant. Adult L. delicatula reared with or without access to A. altissima were ground up and incorporated into separate batches of suet that were placed into double sided feeders set up at different sites during the winter. Trail camera video was reviewed to record how many times birds pecked each suet cake. Birds pecked the suet containing L. delicatula reared without access to A. altissima significantly more frequently than the suet containing adults that had fed on A. altissima. Of the quassinoids sequestered by L. delicatula from phloem sap of A. altissima, ailanthone and four other quassinoids were identified and quantified in different tissues, with the highest concentrations in the salivary glands. Results suggest that sequestration of toxic chemicals from A. altissima provides some protection to L. delicatula from avian predators.

Wildfires are increasingly affecting boreal conifer forests, altering their chemical defences and carbohydrate reserves in ways that may affect their susceptibility to subsequent herbivore threats. We quantified monoterpenes and non-structural carbohydrates in the phloem of lodgepole pine across three treatments (unburned, burn-year, one-year post-fire) to identify fire-induced chemical changes and their temporal dynamics. Monoterpene concentrations rose sharply immediately following the fire but declined after one year. Non-structural carbohydrates showed compound-specific responses: starch and sucrose concentrations reduced post-fire, with partial recovery of sucrose, while glucose increased, and fructose exhibited a delayed response. Multivariate analysis revealed sucrose, starch, and specific monoterpenes as key compounds distinguishing the treatments. Elevated monoterpene concentrations immediately post-fire likely decreased susceptibility to insects; however, the subsequent decline in defences and accumulation of sugars suggest the emergence of a distinct post-fire window of increased vulnerability. These findings improve our understanding of fire-induced chemical shifts and can help predict forest vulnerability to interacting biotic stressors under a changing climate.

Plants and insect herbivores are in a constant co-evolutionary arms race. Plants are always under the threat of insect herbivory and need to employ defenses against insect herbivores, which in turn employ counter defense strategies. The salivary enzyme glucose oxidase (GOX), found in many caterpillar species, has been documented to attenuate defenses in plants such as Nicotiana tabacum (cultivated tobacco). However, in Solanum lycopersicum (cultivated tomato), glucose oxidase elicits defensive responses. Multiple mechanisms have been proposed for how GOX affects plant signaling, but there is still considerable disagreement about which is correct. In this review, we review existing models on the mode of GOX action and propose a new model to fill in research gaps and better explain the mechanism behind GOX action. Our model, coined the "ROS Threshold-Dependent Defense Toggle Model", proposes that whether a plant activates jasmonic acid or salicylic acid-mediated defenses depends on the amount and persistence of hydrogen peroxide whose levels are dependent upon ROS-scavenging capabilities of the plant. We also emphasize the use of cultivated tomato as a model system to test our proposed model.

The identity of trail following pheromones secreted by the ant Lasius flavus were investigated using bioassay-directed fractionation techniques. Extracts of whole bodies were fractionated by high performance liquid chromatography and fractions tested for trail following activity in circular bioassays. Active fractions were analysed by gas chromatography- mass spectrometry (GC-MS) and structures of potential pheromones were confirmed by comparison with synthetic standards. The pheromones 2,6-dimethyl-5-heptenol (DMH) and mellein were identified in active fractions from extracts of whole body and headless ants respectively. Targeted analyses revealed that DMH was detected in the heads of worker ants at a concentration (mean ± SD) of 1.12 ± 0.58 ng per head. Mellein (stereoisomer not identified) was detected at 5.56 ± 1.4 pg per hindgut which was the lowest concentration of this compound detected in an ant species. In comparative bioassays of commercially available standards, (R)-mellein resulted in trail following activity at 0.01 pg per cm which is the lowest known detectable concentration of a pheromone by an ant, whereas a stereoisomeric mixture of DMH was 100-fold less active. These pheromones were tested for alarm activity by measurement of the mandible opening response in L. flavus worker ants. Standard DMH was found to cause a heightened level of aggression in at concentrations of ≥ 1 pg/l, indicating a likely function of an alarm pheromone. The response to (R)-mellein at the same concentrations was always lower, in keeping with its primary function of a trail following pheromone. This work reveals that bioassay directed fractionation can be a useful approach to identify the different behavioural pheromones in a social insect.

endo-Brevicomin, a pheromone component for tree-killing bark beetle Dendroctonus frontalis Zimmermann, the southern pine beetle, has a "peaked," biphasic dose-response, being synergistic with attractants (pheromone component frontalin and host odors) at low release rates and attraction-reducing at high rates. Displacing an endo-brevicomin release device up to tens of meters from an attractant-releasing trap can increase synergistic effects. We investigated the interaction of endo-brevicomin device release rate and displacement. When one of a pair of 6 m distant, attractant-baited traps received an endo-brevicomin device varying in release rate across four orders of magnitude, catches in the endo-brevicomin amended and unamended traps peaked at the same, intermediate release of endo-brevicomin. However, catches were higher in the trap lacking endo-brevicomin at all but the lowest release rates, at which catches did not differ. When endo-brevicomin releasers were placed varying distances from an attractant-baited trap, tested release rates (0.45, 3.4, and 24 mg/d) enhanced catches at 4, 8, or 16 m distance, but, at 0 m, catch enhancement occurred only at the lowest rate and the highest rate produced catch reduction or no change. Our results indicate that endo-brevicomin releasers simultaneously produce long-range attraction-enhancing and short-range attraction-reducing effects for D. frontalis. These effects may promote switching of attack focus to adjacent hosts and propel growth of infestations. Our findings also indicate that maximum augmentation of trap catches should occur with the endo-brevicomin device displaced. Displacement short distances may preserve endo-brevicomin's long-range attractive effects while lessening short-range inhibitory effects.

The whitefly, Bemisia tabaci, is a significant pest in tomato production, causing extensive damage and economic losses. In pursuing sustainable pest management strategies, this study investigates the deterrent effects of Tagetes species (T. erecta, T. patula, and T. minuta) and Crotalaria juncea on B. tabaci settlement and oviposition on tomato plants. Two free dual-choice experimental setups were conducted in a climate-controlled chamber. The study confirmed the efficacy of the experimental setup, with similar B. tabaci dispersion and oviposition on the sides with tomato plants alone. When Tagetes or C. juncea was introduced, a significant reduction in B. tabaci settlement and oviposition was observed compared to the tomato control side. To identify the modes of action of the companion plants on B. tabaci, a follow-up experiment, modifying the spatial arrangement of the plants, was set up to discriminate between physical barrier and chemical repellent effects. The findings suggest a potential crossing between repellence and barrier effects for Tagetes species when C. juncea acted as a sinkhole, trapping the whiteflies. A DHS-ATD-GC-MS analysis revealed that the repellent effect seems more associated with the composition than the intensity of the blend. Some already known repellent volatile compounds of Tagetes, such as limonene, were identified, but the major ketone compounds must also be tested. This study demonstrates the effectiveness of Tagetes and Crotalaria species as biocontrol plants in pest management for tomato production. These plants reduce pest pressure and support sustainable agriculture, offering an alternative to chemical pesticides. Further research should investigate mechanisms, field applications, and broader agroecological benefits.

Billions of specimens are housed in museum collections, but only a fraction are used in research after accession. The chemical composition of museum specimens, such as the presence of plant secondary metabolites (PSMs), is a useful component of the extended museum specimen concept. However, most of the work investigating chemistry of museum specimens has focused on herbarium specimens and not insects, of which some species may sequester and retain plant secondary metabolites. Also, the preparation techniques involved in entomological collections vary substantially and may influence the ability to detect sequestered compounds. The present work uses two Euphydryas butterfly species, E. phaeton and E. anicia (Nymphalidae), that sequester one group of plant secondary metabolites, iridoid glycosides, to ask two questions about the detection of sequestered compounds in museum specimens: (1) Can sequestered iridoid glycosides be detected in insect museum specimens and if so, how far back in time can we detect them? and (2) Do the preparation techniques used on insect specimens impact sequestered iridoid glycoside content? We detected sequestered compounds in insect museum specimens dating back to 1933. We also found that freshly collected specimens had significantly higher amounts of stored defenses compared to all other treatments. This work highlights the potential for use of museum specimens in chemical ecology and informs collections interested in adding chemical content to their extended museum specimen data.

Odorant-binding proteins (OBPs) and odorant receptors (ORs) are regarded as key proteins in the moth olfactory system. Sensory neuron membrane proteins (SNMPs) are also thought to play important roles, although the underlying mechanism remains elusive. Three SNMP genes, two candidate PBP genes, and three candidate PR genes were identified from Clostera restitura. Phylogenetic analysis showed that CresSNMP1 × 1 and CresSNMP1 × 2 were paralogs belonging to the lepidopteran SNMP1 subfamily, whereas SNMP2 consistently clustered within the SNMP2 clade. Only CresSNMP1 × 1 exhibited male-biased expression in adults, whereas SNMP2 presented an extremely high expression level in adult antennae and a stable expression profile from 1st to 5th instar larvae. These findings align with the well-established role of SNMP1 in pheromone detection, whereas SNMP2 may have both olfactory and nonolfactory functions. Multi-protein docking and split-ubiquitin yeast two-hybrid assays indicated that CresSNMPs, especially SNMP1, interact with both OBPs and candidate ORs, suggesting that SNMPs may function as molecular bridges between OBPs and ORs, facilitating the transfer of odorant molecules from OBPs to a specific OR subunits within the heterotetrameric complex.

Microbial volatile organic compounds (VOCs) are key modulators of insect behavior. These low molecular weight compounds influence ecological interactions and hold potential as sustainable agents in pest control. Sitophilus zeamais, a major pest of stored maize worldwide, causes significant post-harvest losses. While fungal VOCs have been studied in grain storage systems, bacterial-insect interactions remain poorly understood. This study evaluated the effects of VOCs emitted by four Enterococcus strains isolated from maize grains on the behavior and mortality of S. zeamais. Maize grains were inoculated with bacterial cultures, and VOCs were identified using gas chromatography-mass spectrometry. Behavioral responses were assessed in a two-choice olfactometer using both bacterial blends and individual pure compounds at varying concentrations. Additional assays included fumigation tests for toxicity and evaluation of oviposition behavior through egg staining in treated grains. Results showed that bacterial VOCs significantly affected the behavior and survival of S. zeamais, supporting their bioactive potential and involvement in interspecific interactions. Acetoin, acetic acid, and diacetyl were identified as the predominant volatiles. Among them, acetic acid acted as a repellent while also stimulating oviposition, acetoin functioned as an attractant, and diacetyl stood out for its toxicity, with effects observed even at low concentrations. These findings highlight the ecological relevance of bacterial volatiles in modulating insect behavior in stored grain systems and contribute to a broader understanding of the chemically mediated interactions between microorganisms and insects in confined environments.