Chemoecology最新文献

Wild bees are heavily declining worldwide except for a few species, such as Colletes hederae, which is spreading in its distribution throughout Europe. Colletes hederae mainly forages on ivy (Hedera helix) which is widespread in Europe and the plants’ availability is thought to contribute to the successful spread of C. hederae. A rapid location of the plants using visual and/or olfactory floral cues would allow the bee to efficiently forage. Beside bee visitors, the flowers attract a high variety of other insects, such as Vespula wasps that were recently investigated regarding their floral-cue preferences. The aim of this study was to investigate the communication between C. hederae and its H. helix host flowers, and to compare the results with that previously obtained with V. germanica wasps. We identified headspace compounds detectable by the bees using gas chromatography coupled to electroantennography (GC-EAD) and performed behavioral experiments to both compare the attractiveness of visual and olfactory floral cues and to determine the attractiveness of a synthetic mixture composed of physiologically active compounds. In the GC-EAD analyses, bees responded to 15 flower-specific compounds of various chemical classes, of which 4-oxoisophorone, (E)-linalool-oxide furanoid, and acetophenone were the most abundant in the floral scent. In the bioassays, visual and olfactory flower cues were equally attractive for bees, but a combination of both cues was needed to elicit not only approach responses but also landings. A synthetic mixture of the EAD-active compounds was attractive to the bees, but to a lesser extent than the natural scent of H. helix flowers. The bees’ integrations of different floral-cue modalities in its search image and its strong antennal responses elicited by various floral scent compounds make C. hederae highly effective in finding its host flowers. In comparison to V. germanica wasps, the bees relied stronger on visual cues than the wasps do, but both species showed the highest attraction when presented with a combination of the cues.

Among non-essential heavy metals, cadmium (Cd) pollution in soil continuously increasing by anthropogenic activity such as agriculture fertilizer and industrial sources worldwide and have several harmful impacts on plants and humans. Andrographis paniculata is a highly medicinal plant having diverse range of SMs like andrographolide (AG). The present study was carried out to investigate the effect of Cd on growth, activity of antioxidative enzymes and andrographolide production of A. paniculata. Cd was applied as cadmium chloride (CdCl₂) at 5, 10 and 15 μg g⁻¹ of soil. All the studied treatments of Cd were found to be toxic for A. paniculata. The root-shoot length, root-shoot fresh weight, root-shoot dry weight decreased with increasing concentrations of Cd. Total phenolics and flavonoids content significantly increased with increasing Cd concentration in soil. The activity of catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol peroxidase (GPX) and polyphenol oxidase (PPO) increased with increasing concentration of Cd compared to control plants. The maximum activity of CAT, POX, APX, GR, GPX and PPO was observed at 15 µg Cd g⁻¹. The AG content in the leaves of plants increased with Cd application. Maximum AG content was observed at 10 μg g⁻¹ applied dose of Cd. Out of the concentrations studied 5 and 10 μg g⁻¹ were moderately toxic to A. paniculata and produced maximum amount of AG.

The olive fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the major insect pest for olive production in the Mediterranean basin and worldwide. Monitoring of its populations is vital for efficient management to avoid yield losses. Olive fly adults are attracted to protein-based food lures. Various protein-based lures are used either for monitoring olive fly populations or for pest management in combination with insecticides. We used two techniques, i.e., dynamic headspace (DHS) and solid-phase microextraction, (SPME) for headspace collection of volatile organic compounds (VOCs) emitted from a commercially available protein-based food lure to identify specific VOCs that attract the olive flies. The collected VOCs were identified with GC–MS and electroantennographically tested with GC–EAD. Both sampling methods isolated a substantial number of VOCs but certain compounds were detected by only one of the two methods. In SPME, more alkyl-substituted pyrazines were detected rather than in DHS. VOCs from various chemical classes provoked electroantennographic responses. Μature mated females gave more responses compared to virgin ones. Both age groups of B. oleae female adults showed electrophysiological responses to 2,5-dimethyl-pyrazine which had lower abundance than the major compound 2,3,5-trimethyl pyrazine. Selected compounds were tested in field trials for attraction of olive fly adults. The highest number of olive fly adults was caught with sticky traps baited with the terpene nonanal. The importance of the collection method in identifying VOCs that might contribute to better monitoring and management of olive fly populations in the field is discussed.

The cypress bark beetle, Phloeosinus aubei (Coleoptera, Curculionidae, Scolytinae) prefers to build breeding galleries in decaying host trees. However, volatile cues specific to decaying or actively infested trees have not yet been reported. Any such information would be useful for the management of this invasive, wood-boring species that has become established across Europe in the temperate zone and is now a key pest of ornamental Cupressaceae in nurseries and urban landscapes. Our objective was to reveal key components in host volatiles specific to stressed trees, which could be potential signals for the pest of its suitability for colonisation. Volatile profiles of arborvitae, Thuja occidentalis ‘Smaragd’ suffering from either dehydration or fresh infestation of P. aubei was collected and compared to that samples from healthy control trees. Analyses of volatiles by gas chromatography coupled to an electroantennographic detector revealed substantial differences between healthy, dehydrated and infested trees. Structural elucidation of the major antennally active components revealed that both α-pinene and α-thujene were prevalent in the volatiles of infested trees, whilst α-thujone was the major component in volatiles of healthy trees. In volatiles collected from trunks housing fresh P. aubei female nuptial chambers, sharp increases of β-pinene, myrcene, limonene, and p-cymene were noticed, alongside trace amounts of camphene and fenchene. Volatiles collected from fresh frass showed a similar profile, but with a somewhat smaller amount of limonene. Fenchone was present in each type of volatiles, however, only in low amounts. Further studies should be directed to reveal the behavioural role of these components, which could be helpful in developing kairomone-based techniques for monitoring the flight of the pest in stands of scale-leafed trees.

Spondyliaspis cf. plicatuloides and Glycaspis brimblecombei (Hemiptera: Aphalaridae) are invasive insect pests of Eucalyptus, native to Australia. The insects feed on eucalypt sap, and both psyllid species exhibit clear preferences for different species and hybrids of Eucalyptus. The objective of this study was to identify the constitutive morphological and phytochemical characteristics underlying these host preferences. Four preferred and eight non-preferred eucalypt hosts were selected for evaluation. Thirteen leaf morphological features of the 12 eucalypts were analysed. The non-polar and polar metabolites in and on the surface of leaves of each eucalypt species were extracted, and their chemical composition was analysed using gas chromatography coupled with mass spectrometry. The leaf volatile profiles of hosts and non-hosts of S. cf. plicatuloides and G. brimblecombei did not differ sufficiently to explain the host choices of the two eucalypt psyllids. The leaf polar metabolite profiles of the susceptible hosts of the two psyllids differed significantly but did not explain the host preferences of the two psyllid species. However, preferred hosts of S. cf. plicatuloides and G. brimblecombei had some leaf morphological features and wax metabolites in common. Our results show that particular combinations of leaf morphological features and wax metabolites might influence the host choice of eucalypt-feeding lerp psyllids, but no traits explaining the differences in host-selection behaviour between S. cf. plicatuloides and G. brimblecombei were identified.

The oil gland secretion of the oribatid mite Nothrus palustris is known to show the phenomenon of juvenile–adult polymorphism, i.e., juvenile instars produce secretions predominated by geranial, whereas adults secrete dehydrocineole along with a number of chemically unidentified compounds. We here re-analyzed the secretions of adult N. palustris by GC–MS and NMR spectroscopy, eventually identifying the unknown compounds as p-menthane monoterpenoids. The major components were two isomeric 6-isopropenyl-3-methyl-cyclohex-3-en-1-yl formates (= p-1,8-menthadien-5-yl formates), which accounted for about 75% of the secretion. These were accompanied by five additional, only partly identified p-menthanes (or p-methane-derivatives), all of which represented minor or trace components. In addition, adult secretions contained two C₂₁-hydrocarbons, 1,12-heneicosadiene (major) and a heneicosatriene (minor). Menthane monoterpenoids represent a novel sub-class of terpene compounds in the oil gland secretions of Oribatida. In case of N. palustris, we assume that both geranial and p-menthane monoterpenoids arise via the mevalonate pathway which obviously shows a split at the level of geranyl pyrophosphate, leading to geranial in juveniles and to p-menthanes in adults. The significance of methane occurrence in oil glands as well as the taxonomic distribution of juvenile–adult polymorphism in oribatid oil gland secretions is discussed. The latter phenomenon—i.e., “chemo-metamorphosis” of secretions—is not known from early- and middle-derivative Oribatida nor from Astigmata, but appears to be more common in some derivative desmonomatan and brachypyline oribatid groups.

The South American locust, Schistocerca cancellata (Serville 1838), is considered to be the most serious agricultural pest in Argentina and neighboring countries. The species is famous for the strong and pleasant aromatic scent of mature males in the gregarious phase. We identified this fragrance as a mixture of two main aromatic compounds, benzyl alcohol, and 2-phenylethanol. The male-specific volatiles are emitted almost exclusively from the abdomen. The release of the male volatiles is linked to sexual maturity and is influenced by the intensity of sexual competition between males. Consequently, a function of the volatiles as a gregarious mature male-emitted pheromone in the context of reproduction is obvious. No female-specific volatiles were found. Some compounds of the semivolatile fraction of the cuticular hydrocarbon (CHC) profile were also detected in the headspace of both sexes. This fraction of the CHCs of S. cancellata consists almost entirely of unbranched C23 to C31 alkanes. The profiles vary slightly between the sexes and differ from the reference profile of the prominent and well-studied species S. gregaria. Thus, semivolatile components of the CHCs may also play an important role in the short-range mate recognition system of the species.

The importance of plant cuticular waxes in plant–herbivore interactions has become an area of increasing interest, but it has been poorly explored in chrysomelid beetles, one of the most important groups of insect pests. In this study, we investigated the effects of cuticular wax on feeding behaviors of Aulacophora femoralis (Chyrosomelidae), a pest of Cucurbitaceae crops. We analyzed chemical compositions of leaf cuticular waxes using gas chromatography–mass spectrometry. The compositions were significantly different among plant species; in particular, host (Cucumis maxima, C. pepo, C. sativus, Cucurbitaceae) and non-host (Pueraria lobata, Fabaceae) leaves had distinctive compositions of cuticular waxes. We examined if the cuticular wax induces feeding behaviors based on a bioassay using filter papers treated with cuticular wax extract from host or non-host leaves, or a synthetic mixture of straight-chain alkanes (n-alkanes), major components of the host cuticular waxes shared among different host species. We found that the beetles frequently left bite marks on the filter papers treated with n-alkanes but less frequently on those treated with cuticular wax extracts of host leaves. These results indicate that leaf cuticular wax n-alkanes stimulate feeding behavior, but are not cues for host selection.

Coniferous trees of the genus Pinus (Pinaceae) are under continuous threats by numerous herbivorous insect species and pathogens attacking nearly all parts and tissues of the plants. To defend themselves, pine trees produce large amounts of oleoresin that is accumulated in a highly developed network of specialized resin ducts, which are distributed in the wood, bark, and needles. Such defense reactions in pines can be induced by the attack of herbivores. The banded pine weevil, Pissodes castaneus (De Geer, 1775) (Coleoptera, Curculionidae), is an important pest of Pinus in Brazil, where it has been an invasive species since 2001. The female lays its eggs under the tree bark of trees and the larvae feed in the phloem of the trunk and branches, interrupting the sap circulation and eventually causing its death. In the present study, we conducted detailed GC–MS analyses of volatiles emitted by twigs of Pinus taeda L. We analyzed how the attack by P. castaneus males and females affects the volatile pattern emitted by the twigs. When comparing volatiles produced by healthy plants and by female- and male-attacked P. taeda, qualitative and quantitative differences were detected, as the decreased production of limonene, germacrene D and (E)-caryophyllene and the increase of α-pinene. Laboratory bioassays showed that plants attacked by male and female P. castaneus were more attractive to the insects. Understanding about what compounds may attract or repel the insects may help in the development of more effective traps, as well as preventing stress to avoid infestation.

Although recognition using cuticular chemistry is important for host–parasite interactions within aculeate Hymenoptera, cuticular hydrocarbon (CHC) profiles of only a few host–parasite pairs were characterized and compared. One largely neglected family in this context is the Mutillidae (velvet ants), whose species are ectoparasitoids of bees and wasps. In our study, we characterized and compared the CHC profiles of five species of Mutillidae and seven host species. The CHC profile of velvet ants differed among species and included large proportions of n-alkanes and methyl-branched alkanes. Alkenes were much less abundant in the CHC profiles of three species of velvet ants compared with their hosts, while the other two species possess a much lower abundance of methyl-branched alkanes than their hosts. Both the number of peaks and compound diversity were generally higher in velvet ants compared with their hosts. Thus, CHC profiles of parasitoids did not show signs of mimicry when compared with their hosts. In dyadic encounters between one species of velvet ant and its host bee species, the parasitoid mainly avoided interacting, while aggression by the host was rare. Our results suggest that velvet ants did not evolve chemical mimicry, perhaps in accordance with their wide host spectrum which would limit chemical specialization. However, the reduction of alkenes in social bee-attacking species and the reduction of methyl-branched alkanes in social wasp-attacking species may favour host nest invasion, since these two CHC classes are known to be important in nestmate recognition for social bees and wasps, respectively. A larger, phylogeny-corrected comparison of Mutillidae and hosts may help clarifying the evolution of the CHC profile of these parasitoids.