Journal of Chemical Ecology最新文献

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.

Olfactory imprinting is evident when animals respond differently to olfactory cues later in life as a result of experiencing those cues during a sensitive window that occurs early in development. The cues can consist of single chemicals or complex mixtures. Responses to mixtures are complicated, as mixtures can contain odorants that evoke dissimilar responses in unimprinted adults. For example, salmon appear to imprint to amino acid mixtures, yet individual amino acids can evoke attraction, avoidance, or indifference. We aimed to dissect how odorants that evoke dissimilar behavioral responses contribute to mixture imprinting. For this, zebrafish were developmentally exposed to L-leucine, L-lysine and L-valine, or β-phenylethyl alcohol (control), grown to adulthood, and then their preference responses to the same chemicals were measured. Imprinting was apparent to β-phenylethyl alcohol, L-leucine, and L-lysine, but not to L-valine. The responses to L-leucine, and L-lysine were opposing as they evoked attraction and avoidance, respectively. As adults, fish imprinted to a mixture of L-leucine, and L-lysine only responded to the same mixture, not its constituents. This supports the contention that an imprinting cue behaves as a unique object, regardless of its complexity. However, the imprinting response to the mixture was biased by the aversive amino acid, which indicates the imprintable constituents can have different weights. For species that use amino acid profiles to guide their migration, it appears the contributions that any given amino acid makes to the mixture may be quite important.

While intraspecific trait variation can regulate ecosystem functions, there is limited understanding of whether this variation caused by inducible phenotypic shifts, as opposed to genetic hardwiring, can have such effects. Leveraging the complex inducible defense systems of plants, we found that treating young Alnus rubra trees with the plant hormones methyl jasmonate and salicylic acid, which are involved in plant defensive responses to herbivory and/or pathogen stress, triggered shifts in the composition of leaf secondary metabolites and nutrient reallocation among plant tissues. Induction of the jasmonic acid pathway triggered substantial changes among the dosage-dependent ellagitannins and a decline in leaf nitrogen, while induction of the salicylic acid pathway triggered greater restructuring among the cytotoxic diarylheptanoids. Concurrent induction of both pathways caused distinct changes in leaf composition compared to either pathway alone. We also found opposing seasonal trends of these two major classes of secondary metabolites with seasonal declines among diarylheptanoids and increases among ellagitannins. Further, these plant hormone-induced compositional changes in leaves had cascading effects on ecosystems, with litter mass loss rates in both aquatic and terrestrial ecosystems inhibited most by induction of the jasmonic acid pathway, least by induction of the salicylic acid pathway, and effected at intermediate levels by the combined induction of both pathways. These results demonstrate that inducible plant defenses that are mounted against terrestrial stressors can alter rates of litter mass loss in aquatic and terrestrial ecosystems.

Groundnut plants subjected to root herbivory by Odontotermes obesus exhibited significant changes in the behavioural responses of Spodoptera litura, characterized by reduced oviposition rates and modified feeding preferences compared to healthy plants. Our findings provide strong evidence that groundnut plants under termite attack mobilized both metabolic and volatile defenses to mitigate further herbivory, supporting the defense induction hypothesis. The elevated levels of phenols, sugar alcohols (D-Pinitol, D-Allose, D-(+)-Xylose), and insecticidal fatty acids (9-Octadecenoic acid, 10-Undecenoic acid) demonstrate a coordinated shift in primary metabolism aimed at reducing herbivore performance. Simultaneously, the altered volatile organic compound emissions (alkanes, alkenes, tetradecane) suggest an indirect defensive strategy, potentially recruiting natural enemies or disrupting host-finding cues of S. litura. These findings demonstrate that below-ground termite herbivory induces significant metabolic shifts in plants, which in turn modulate S. litura oviposition behaviour and larval feeding preferences, highlighting a complex cross-trophic interaction between root and shoot herbivores.