Chemoecology最新文献

A vast diversity of parasites associates with ants. Living in and around ant nests of these organisms must overcome ant colony defenses. As ant defensive behavior is mainly mediated by species-specific cuticular hydrocarbons (CHCs) or alarm pheromones, and ant-associated parasites can either crack their hosts’ chemical communication code by modifying their own CHC profiles or use pro-active strategies like chemical weaponry for distraction and repellency. While the chemical nature of ant–parasite interactions has been intensively studied for highly host-specific parasites, the chemical-deceptive strategies of the rather rare ant-resembling heteropterans are unknown. To gain insight into this system, I studied the bug Scolopostethus pacificus (Barber 1918) which can be found near the nests of the ecologically dominant and aggressive velvety tree ant (Liometopum occidentale, Emery 1895). Using behavioral, chemical, and molecular approaches, I disentangled the relationship of S. pacificus and its host ant. Chemical profiling of the bug and the ant revealed that the bug does not make use of CHC insignificance or mimicry, but instead uses a cocktail of volatile compounds released from its metathoracic glands that likely moderates encounters with its aggressive host. Feeding trials with armed and artificially disarmed bugs revealed a defensive function of the gland exudates. Targeted molecular gut barcoding showed that S. pacificus does not feed on L. occidentale. These results suggest that chemical weaponry, rather than a chemical code-cracking CHC matching or chemical insignificance, enables S. pacificus to get along with and live in close proximity to its host ant.

The scent gland secretion of an undetermined species of Prionostemma from Costa Rica was analyzed by gas chromatography–mass spectrometry and shown to consist of medium-chain carboxylic acids (mainly octanoic acid) and a ß-hydroxy-carboxylic acid, eventually identified as myrmicacin (= (R)-3-hydroxydecanoic acid). While scent gland secretions in harvestmen have traditionally been considered to be products of de novo synthesis, we here provide evidence for the unusual case of sequestration-derived scent gland constituents: at least myrmicacin appears to be sequestered from leaf-cutter ants that constitute a part of the prey of the Prionostemma-species herein investigated. This is the first report on the scent gland chemistry of the sclerosomatid subfamily Gagrellinae as well as on a possible sequestration mechanism in harvestmen.

Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a notorious pest of rice, Oryza sativa L. (Poaceae). Sex pheromones and host-plant volatiles can trap C. medinalis separately. To improve the trap efficiency of synthetic sex pheromone blend, we first tested the synergistic effect of 8 host-plant volatiles, including 2-phenylethanol, 1-hexanol, 1-heptanol, (Z)-3-hexenal, (E)-2-hexenal, octanal, valeraldehyde, and methyl salicylate, on the attraction of C. medinalis to the female-produced sex pheromones in electroantennography. The addition of (E)-2-hexenal, methyl salicylate, valeraldehyde, and (Z)-3-hexenal increased electroantennogram response of C. medinalis to sex pheromones. Further behavioral testing in wind tunnel experiments indicated that additive (E)-2-hexenal or methyl salicylate stimulated the landing behaviors of both male and female C. medinalis compared with sex pheromones alone. Field evaluations showed that mixtures of sex pheromones and (E)-2-hexenal /methyl salicylate resulted in significantly higher catches to male moths than sex pheromones alone. Using 1:1 and 1:10 combinations of the sex pheromones and (E)-2-hexenal, the attraction of C. medinalis to mixtures showed a synergistic effect of 95% and 110%, respectively. Furthermore, 1:1 and 1:10 mixtures of the sex pheromones and methyl salicylate exhibited a synergistic effect of 69% and 146%, respectively. These results may provide the basis for developing efficient pest management strategies against C. medinalis using host-plant volatiles and insect sex pheromones.

Cover crops provide many agroecosystem services, including weed suppression, which is partially exerted through release of allelopathic benzoxazinoid (BX) compounds. This research (1) characterizes changes in concentrations of BX compounds in shoots, roots, and soil at three growth stages (GS) of cereal rye (Secale cereale L.), and (2) their degradation in soil over time following termination. Concentrations of shoot dominant BX compounds, DIBOA-glc and DIBOA were lowest at GS 83 (boot). The root dominant BX compound, HMBOA-glc, concentration was least at GS 54 (elongation). Rhizosphere soil BX concentrations were 1000 times smaller than in root tissues. Dominant compounds in soil were HMBOA-glc and HMBOA. Soil BX compound concentrations were similar near root crowns and between-rows. Soil BX concentrations following cereal rye termination declined exponentially over time in three of four treatments: incorporated shoots (S) and roots (R), no-till S + R (cereal rye rolled flat), and no-till R (shoots removed); no-till S had consistently low concentrations. In treatments showing changes, soil concentrations of HMBOA-glc and HMBOA increased above initial concentrations on the day following cereal rye termination. Concentrations of these two compounds decreased more rapidly than the other compounds. Placement of shoots on the surface of an area where cereal rye had not grown (no-till S) did not increase soil concentrations of BX compounds. The short duration and complex dynamics of BX compounds in soil prior to and following termination illustrate the limited window for enhancing weed suppression directly by cereal rye allelochemicals; valuable information for programs breeding for enhanced weed suppression.

Juvenile hormone (JH) is a key insect hormone involved in the regulation of physiological, developmental and behavioural processes. In social insects, it has been shown that JH can play a key role in modulating reproductive division of labour, age-related division of labour and chemical signalling, and can display marked changes in function of the degree of sociality. Here, we checked the effects of JH on reproduction in single foundresses of two neotropical primitively eusocial wasp species, Mischocyttarus cerberus and Mischocyttarus cassununga, by examining how treatments with the JH-analogue methoprene and the anti-JH precocene affect egg-laying, ovarian activation and chemical profiles. Our hypothesis was that reproduction and the production of particular fertility-linked cuticular hydrocarbon cues might be under shared JH control already in primitively eusocial wasp species, and this could have been a key enabler to allow such cues to later evolve into full-fledged queen pheromone signals in advanced eusocial species. In line with this hypothesis, we show that our hormone treatments significantly affected both egg laying and the production of particular hydrocarbons present on the egg surface. We discuss the relevance of these findings in the context of the evolution of social insect queen pheromones in advanced eusocial species with a morphologically differentiated queen–worker caste.

Quinones are one of the major pigment groups that provide such bright colors to feather stars (Echinodermata, Crinoidea). These secondary metabolites also act as defensive molecules rendering crinoids unpalatable and repellent to other organisms. However, feather stars are usually associated with numerous symbiotic organisms, amongst which the ectocommensal snapping shrimp Synalpheus stimpsonii. We investigated the chemical stimulus allowing host selection in S. stimpsonii through the combination of behavioral tests, chemical extractions, and mass spectrometry analyses. The individuals of S. stimpsonii used in the experiments were sampled around the Great Reef of Toliara (Madagascar) where they are found in association with two crinoid species: Comanthus wahlbergii and Phanogenia distincta. The chemical attractiveness of the two crinoid hosts and a non-host species, Cenometra bella, was tested in an olfactometer. The three crinoids produced attractive kairomones allowing the snapping shrimp to recognize them. Mass spectrometry analyses on purified extracts of P. distincta revealed the presence of three different anthraquinones (rhodoptilometrin, comantherin, and a new crinoid anthraquinone). Compared to the existing literature, this anthraquinonic cocktail is specific to P. distincta. When these extracts were injected in the olfactometer, they triggered similar attracting behavior suggesting that crinoid anthraquinones are kairomones allowing host selection for S. stimpsonii. This hypothesis is also supported by the fact that shrimps were chemically attracted by pure commercial anthraquinones. In addition to their traditional defensive role (allomones), anthraquinones would, therefore, also function as kairomones, maintaining the symbiosis between S. stimpsonii and its crinoid hosts.

Luteolin 7-O-glucoside (1), 10β-acetoxy-8α-butyryloxy-11α-hydroxy-2β-((2-methylbutanoyl)oxy)-1βH,6αH,7αH,11βH-guaian-3-en-12,6-olide (2) and thapsigargin (3) herbicidal activities’ were evaluated in comparison with their binary and tertiary mixtures, against Lolium perenne. These allelochemicals were isolated from Thapsia garganica leaves methanolic extract. Experiments were carried out by irrigation and spray in pot trials. Each compound was tested at the concentration that inhibits 50% of L. perenne root growth (IC₅₀). Mixtures were prepared at the total concentration determined to inhibit 50% of weed root growth based upon the IC₅₀ value for each compound (1000 µM, 154 µM and 300 µM for 1, 2 and 3, respectively). The greatest herbicidal effect was observed in tertiary mixtures, followed by binary ones, and single compounds showed the lowest phytotoxicity. Moreover, spray treatment was more effective at inhibiting growth of L. perenne, compared with irrigation. For sprayed binary mixtures, the 2 and 3 mixture showed the best inhibitions in shoot (75.79%) and root (91.02%) growth, and fresh weight (89.28%). These values significantly improved those of the most active single compound, 1 (48.01%, 58.62% and 57.14%, respectively, following spray). On the other hand, compound 3, whose structure is related to guaianolide sesquiterpene lactones, was a common constituent of the most active mixtures, suggesting that it plays a more relevant role in the improvement of the phytotoxicity of mixtures. Results obtained for the spray treatment of the tertiary mixture of 1 (333.33 µM), 2 (51.33 µM) and 3 (100 µM) were even more prominent, since weed growth was completely inhibited. After irrigation with a tertiary mixture, the greatest inhibitions in shoot and root growth and fresh weight did not exceed 88.16%, 94% and 90.47%, respectively. The results reported highlight a synergistic behavior of the test allelochemicals which could be applied in the development of bio-herbicides.

Green leaf volatiles (GLVs) are initially formed in the form of aldehydes, and then converted to alcohol and ester forms by the enzymes from plants. However, it remains unclear whether and how plant microbes work with aldehyde GLVs, especially under stressed conditions. Here, transcriptional response of cold-pretreated Pantoea agglomerans KSC03, an endophyte from Astragalus membranaceus var. mongholicus roots to E-2-hexenal was investigated and verified by real-time PCR and GC–MS after the time length of cold pretreatment was optimized. The results revealed that a 12-h cold stress was the most effective for KSC03 to trigger positive response to E-2-hexenal as far as the cell density was concerned. Transcriptome analysis showed that differentially expressed genes induced by E-2-hexenal were enriched in the following pathways: ABC transporter, phosphotransferase system, nitrotoluene degradation, and metabolisms of hexose and butanoate. Amongst, the upregulated transcription of gene3176 and gene4782 encoding N-ethylmaleimide reductase and diacetyl reductase in E-2-hexenal treatment was confirmed by real-time PCR. So did the enhanced production of 2,3-butanediol triggered by E-2-hexenal. Additionally, the transcription of gene3176 and gene4782 and the production of 2,3-butanediol chronologically reached their peaks in the E-2-hexenal-treated cells at the stationary phase. The results also indicated that exogenous E-2-hexanal passed through the cell membrane at the lag/early logarithmic phase and could not be utilized directly. In summary, E-2-hexenal triggers the positive cell response of cold-pretreated KSC03 at the transcriptional and metabolic levels in a time-length dependent manner.

Floral displays constitute signals conveyed to potential pollinators by pigments and fragrance compounds, which are secondary metabolites biosynthesized through a limited number of major metabolic pathways. In recent years, the role of defensive secondary metabolites, targeted to tolerate/resist herbivory, pathogen-borne diseases and other kinds of stress, has become apparent in the context of floral displays. Apart from pigments and volatile compounds, these defensive compounds include alkaloids, specialized molecules such as glucosinolates (in Brassicaceae), and proanthocyanidin phenolics. All these functionally overlapping groups of metabolites vary in floral concentrations under different kinds of environmental conditions as well as due to endogenous regulatory factors, resulting in metabolic and functional synergies or trade-offs according to the physiological status of the flowers. In this review, we discuss such associations among varying secondary metabolites in flowers, and their implications in context of plant stress-response mechanisms.

Spiroacetals such as E-7-methyl-1,6-dioxaspiro[4,5]decane (trans-conophthorin; tC) and acetamides [predominantly N-(3-methylbutyl)acetamide; N3MBA], are two major groups of volatiles discovered in venoms of many Vespidae. In the course of testing the attractiveness of tC and N3MBA to Vespidae using Rescue^® Wasp TrapStiks, a significant number of female milichiids, Desmometopa nearctica Sabrosky and D. sordida (Fallén) (Diptera: Milichiidae) were trapped as well. However, the attraction of vespid wasps was not significant at the dosages tested. We found a significant synergistic effect of tC and N3MBA in attracting Desmometopa flies. Both D. nearctica and D. sordida are kleptoparasitic species; and we conclude that females of these two milichiid flies use tC and N3MBA (and likely other volatiles) released from venom glands of the social vespids (yellowjackets, paper wasps and hornets) as kairomones to locate disturbed, injured, or freshly killed insects (vespids and/or their prey) as a protein-rich food source for egg development and production.