Chemoecology最新文献

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.

Carotenoids play multiple roles in insects, including coloration and protection. Most insects can obtain carotenoids only from their diet. Therefore, carotenoids are proposed to reflect trophic chains and lifestyles of insects. We investigated the mini-ecosystem of a gall on a hawkweed Hieracium × robustum induced by the gall wasp Aulacidea hieracii (Hymenoptera: Cynipidae) that is attacked by parasitoid wasp Eurytoma cynipsea (Hymenoptera: Eurytomidae). The parasitoid larvae consume the gall wasp larvae that consume the gall tissues. We employed resonance Raman spectroscopy to trace the fate of carotenoids in living larvae and pupae of these insects. We showed that carotenoid composition in the parasitoid closely corresponds to that of its diet—the gall wasp. On the contrary, carotenoid composition in the gall wasp was independent of that in the gall tissues, and the carotenoid concentration increases as non-feeding larvae mature. Thus, A. hieracii is suggested as a candidate among insects to have the ability to synthesize and modify carotenoids. Our findings give rise to the question of the relevance of using carotenoids as markers of trophic flow in the gall community.

The extend of biogeochemical cycling of nickel (Ni) by tropical hyperaccumulator plants in their native habitat is largely unknown, although these unusual plants are suspected to play a major role in the recycling of this element in ultramafic ecosystems. In this study, we have assessed the biogeochemical cycling of Ni (and other elements, including mineral nutrients) by a tropical Ni hyperaccumulator plant, i.e., Phyllanthus rufuschaneyi, which is one of the most promising species for tropical Ni agromining. The study site was a young secondary forest in Sabah (Malaysia) where Phyllanthus rufuschaneyi occurs as the dominant species on an ultramafic Cambisol. For 2 years, we monitored a 100-m² plot and collected information on weather, biomass increase, soil fertility, water fluxes to the soil and litter fluxes for a wide range of elements, including Ni. The Ni cycle is mainly driven by internal fluxes, notably the degradation and recycling of Ni-rich litter. Over the period of investigation, the Ni litter flux corresponded to the total Ni stock of the litter (5.2 g m⁻² year⁻¹). The results further show that Ni turnover varies significantly with the accumulation properties of the plant cover. This points to the major influence of Ni hyperaccumulator plants in building up Ni available stocks in the topsoils, as has also been shown in temperate ultramafic systems. Litterfall and throughfall contribute substantially to the cycling of phosphorus, sulphur and potassium in this ecosystem, with throughfall contributing 2-, 220- and 20-fold higher to the respective nutrient fluxes relative to litterfall. The magnesium:calcium ratio far exceeded 1 in the soil, but was < 1 in the leaves of Phyllanthus rufuschaneyi. The insights from this study should be taken into account when designing tropical agromining operations; as Ni stocks could be more labile than initially thought. The removal of Ni- and nutrients-rich biomass will likely affect available Ni (and major nutrients) for the next cropping seasons, and requires sustainable fertilisation, to be utilized to replenish depleted major nutrients. These findings also have major ecological implications.

Species-specific pheromone communication in moths is often achieved by the precise control of the production of a multi-component sex pheromone blend in females and selective perception of pheromone compounds in males. Reproductive isolation mediated by sex pheromone can be enhanced by the sensitive detection of structurally related non-pheromone components that are not used as pheromone in the same species but used as pheromone components in similar species. Here, we identified several unsaturated aliphatic acetates inhibiting the attraction of male moths to conspecific female sex pheromone in the lightbrown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), through electroantennogram (EAG) and field trapping studies. In EAG screening with 46 pheromone and structurally related compounds, eleven compounds exhibited significant male-specific EAG responses at 1 µg dose. The EAG-active compounds were mainly mono- or di-unsaturated 14-carbon acetates. In subsequent field trapping tests to evaluate the behavioral activities of the EAG-active compounds on male attraction to the binary blend (E11-14:Ac + E9E11-14:Ac) of female sex pheromone of E. postvittana, each of nine compounds (E9-12:Ac, Z9-12:Ac, E9-14:Ac, Z9-14:Ac, Z10-14:Ac, Z11-14:Ac, Z12-14:Ac, Z9E11-14:Ac and Z9E12-14:Ac) displayed clear inhibition of male moths to the sex pheromone blend in a dose-dependent manner. Our findings provide useful information in understanding the pheromone communication system of E. postvittana and related species.