Chemoecology最新文献

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.

Social wasps build their nests using plant material and can thereby occupy different types of habitats. The organization of their colonies is generally based on complex communication systems that include chemical compounds of the cuticle that are shared with the material of their nests thus contributing to the specific chemical signature of their colony. These compounds can vary by environmental factors, in this case the nesting substrate may interfere with this composition. However, no study to date has investigated whether there is any relationship between the chemical signature of the colony and the nesting substrate of their nests. Therefore, in this study we investigated the relationship between the colonial chemical signature and the plant in which the colonies were nesting. Colonies of three species of social wasps and samples of plants where they nested were collected, then extractions of the chemical composition of adult wasps, nest material and plants were performed. The results show that the colonies of social wasps investigated here share their chemical composition with the plants where their nests were built. Our results suggest that the plant can provide the colony with more than just a place with ideal physical conditions and safety, but also compounds that compose the colonial chemical signature.

Numerous species of herbivorous insects are associated with soybeans, including the specialist velvetbean caterpillar (VBC), Anticarsia gemmatalis, and the generalist fall armyworm (FAW), Spodoptera frugiperda. Expression of plant resistance is influenced by factors intrinsic to host plants, such as leaf age and plant stage, which can differentially affect specialist and generalist insects due to varying levels of plant defense and corresponding insect adaptation. In this study, four experiments were carried out to test the hypotheses that levels of antibiosis-resistance to VBC and FAW in the resistant genotype PI 227,687 and susceptible genotype IGRA RA 626 RR are related to leaf age and plant stage of soybean. Furthermore, the concentrations of nutrients and selected flavonoids were quantified to give insights into possible chemical mechanisms underlying the resistance. As results, development of VBC and FAW were negatively affected when larvae fed leaves of the resistant genotype, older leaves from the lower part of plants, or leaves from reproductive-stage soybeans. The effects were partly different for each insect species, and the generalist FAW was more affected by higher resistance levels in the older leaves of soybean than the specialist VBC. Distribution and concentrations of nutrients and flavonoids in soybean in function of leaf age and plant stage may explain the varying levels of antibiosis-resistance to VBC and FAW. These results can benefit developments of specific protocols for screening resistant soybean genotypes and pest management strategies focused in plant parts and growth stages that insect-resistance levels are lowest.

The behavioral responses of two bed bug species, Cimex lectularius L. and C. hemipterus (F.), to conspecific or heterospecific nymphal aldehyde blends were examined using a two-choice olfactometer. Volatile cues from exuviae or a synthetic blend containing (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and 4-oxo-(E)-2-octenal were tested. In both species, the adults settled preferentially on the olfactometer treatment side when conspecific volatile aldehyde cues were provided. When tested with heterospecific volatile aldehyde cues, only adult C. lectularius preferentially responded to C. hemipterus volatile cues. Adult C. hemipterus was indifferent to the aldehyde blend of C. lectularius. Potential implications of the finding on bed bug biology and practical pest management are discussed.

Bark beetles of the genus Polygraphus have recently been involved in large bark beetle outbreaks in central Sweden, together with the European spruce bark beetle Ips typographus. Three species of Polygraphus can be found in this region; Polygraphus poligraphus, Polygraphus punctifrons and Polygraphus subopacus. Efficient pheromone traps would facilitate further investigations of these species and their role in bark beetle outbreaks. Pheromone compounds have previously been identified in P. poligraphus and P. punctifrons, but not in P. subopacus. Thus, we allowed males and females of P. subopacus to bore in the bark of stem sections of Norway spruce (Picea abies) in the laboratory. Volatile organic compounds from boring insects were sampled with SPME and analysed with GC–MS and several male-specific compounds were observed. The male specific compounds were 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, 3-methyl-2-butenal, grandisol, fragranol, (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol, (E)-2-(3,3-dimethylcyclohexylidene)-ethanol, (Z)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, (E)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, geranial and γ-isogeraniol. (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol, [(Z)-DMCHE], was identified from GC–MS analysis to be the major male-specific compound while the (E)-isomer, [(E)-DMCHE], was found as a minor compound. These two compounds gave positive responses in EAG analyses with antennae from males and females of P. subopacus. Thus, (Z)- and (E)-DMCHE were used in a field experiment in central Sweden but only (Z)-DMCHE was found to be attractive to males and females of P. subopacus. Consequently, (Z)-DMCHE was established to be a component of P. subopacus aggregation pheromone.

Neotropical poison frogs possess alkaloid-based antipredator defenses which they sequester from a diet of arthropods such as oribatid mites and myrmicine ants. Alkaloid sequestration is still poorly understood and although several studies have examined its uptake, most experiments directly feed alkaloids to the frogs. Here, we examined the alkaloid uptake system in the poison frog species Dendrobates auratus by feeding it an alkaloid-containing prey item, the red imported fire ant Solenopsis invicta (Formicidae, Myrmicinae). Captive bred frogs were either fed live ants or fruit flies dusted with powdered ants for 4 months. Using GC–MS, we confirm that S. invicta contain previously described piperidine alkaloids known as solenopsins; however, none of these piperidine alkaloids was detected in the skin of D. auratus, suggesting the frogs are incapable of sequestering solenopsins from S. invicta. It is possible that D. auratus are unable to sequester fire ant piperidines due to their long hydrocarbon side chains, a feature that makes them structurally different than most known alkaloids in poison frogs.

Volatilization, one of the most important mechanisms of the allelopathic effects of an exotic noxious weed Mikania micrantha, has not been adequately investigated to date. In this study, laboratory bioassays showed that the effects of volatiles from the leaves and flowers of M. micrantha on seed germination and seedling growth were negative for all four tested plants (Lactuca sativa, Chrysanthemum coronarium, Bidens pilosa, Abutilon theophrasti). Moreover, the inhibitory effect of the leaf volatiles was generally greater than that of the flower volatiles. To assess the reason for the above differences and further explore which compounds played the most crucial roles, the volatiles from the two tissues were absorbed by solid phase microextraction (SPME) and identified by gas chromatography and mass spectrometry (GC–MS). Then, 19 and 10 terpenes were determined respectively. α-Terpineol, β-ocimene, β-myrcene, α-pinene and caryophyllene had the maximum differences in content and concentration, which were selected for further bioassays with B. pilosa. The results indicated that morphological indices and SOD activity decreased with increasing concentrations of chemicals, whereas the contents of chlorophyll, soluble protein and MDA represented adverse changes. In addition, significant responses were observed in the treatments with α-terpineol at 1.0 μL·L⁻¹ and lower concentrations, while similar trends were observed in the treatments with β-ocimene, β-myrcene, α-pinene and caryophyllene at 10 μL·L⁻¹ and higher concentrations. It was concluded that terpenoids released through volatilization have an important role in the allelopathic effect of M. micrantha, and the oxygenated monoterpene α-terpineol played a crucial role in these effects.

Chemical communication is fundamental to maintain cohesion in social insect colonies, and in this communication process, cuticular hydrocarbons act as cues exchanged during interactions between nestmates. However, few studies have investigated intraspecific variation of these compounds in Neotropical swarm-founding wasps. We undertook the present investigation by performing two assessments. First, we assessed whether the cuticular chemical composition of females in Polybia sericea varies according to the degree ovarian development, relative age and different body parts. Second, we assessed whether the cuticular chemical profile of colony members and compounds found in nest materials could be used as complementary tools to assess population differences. To make these determinations, samples were collected from three different populations, and the compounds were analyzed by gas chromatography coupled with mass spectrometry. Linear alkanes were found to be the most abundant compounds in the cuticle of females and nest material. Considering the cuticular composition, it was possible to distinguish the females according to degree of ovarian development, relative age and different body parts. In addition, cuticular compounds and nest material were different in the three analyzed populations; therefore, both the cuticular chemical profile of colony members and the chemical profile of nest material can be used as complementary tools to assess population differences.