The plant sesquiterpene germacrene D specifically activates a major type of antennal receptor neuron of the tobacco budworm moth Heliothis virescens

Plants release hundreds of volatiles that are important in interactions with insects or other organisms. However, knowledge is scarce as to which of the compounds are detected by the organism's olfactory receptor neurons. In the present study, single receptor neurons on the antennae of the tobacco budworm moth, Heliothis virescens, were screened for their sensitivities to naturally produced plant volatiles by the use of gas chromatography linked to electrophysiological recordings from single cells (GC-SCR). Plant volatiles, collected by aeration of host and non-host plants, were tested on each receptor neuron via parallel GC-columns. Thus, simultaneous recordings of the gas chromatogram and the neuron responses to each component were obtained. One type of receptor neuron, appearing in 80% of all experiments, responded with high sensitivity and selectivity to one particular component, present in host as well as non-host mixtures. The component, identified as a sesquiterpene hydrocarbon by linked gas chromatography-mass spectrometry, was isolated from a sesquiterpene fraction of cubebe oil and identified by NMR as germacrene D. The purified compound was then re-tested via gas chromatography on the same receptor neuron type, verifying the identification. A weaker response to another sesquiterpene hydrocarbon was also recorded.     

Comparison of headspace techniques for sampling volatile natural products in a dynamic system

Commonly used dynamic sorption techniques for collecting biologically active volatile compounds have been compared. Solid phase microextraction (SPME) using two types of fibers (polydimethylsiloxane, PDMS, 100 microm, and carbowax/divinylbenzene, CW/DVB, 65 microm) was compared to purge and trap methods (Porapak Q, Tenax TA and charcoal) and a technique based on absorption in methanol in a cooling bath. Sampling was done in a stream of purified air (20 ml/min) in a closed and temperature-regulated (27 degrees C) glass tube, passing over a capillary tube containing a hexane solution of tridecane, heptadecane, 1-octen-3-ol, 1-hexadecanol, ethyl tetradecanoate, alpha-pinene, linalool, terpinen-4-ol, cis-verbenol, verbenone, beta-caryophyllene, E,E-farnesol, and geranylgeraniol. With all of the methods, the sampling was performed for a period of 30 min before extraction and analysis was done on a GC-FID system. In general, SPME gave a higher response for all compounds except for alpha-pinene, which was only extracted by the CW/DVB fiber. Purge and trap methods and methanol absorption gave the same response for all substances extracted. None of the methods extracted hexadecanol and geranylgeraniol under the conditions used. However, the SPME equipped with the PDMS coating extracted heptadecane, E,E-farnesol and ethyl tetradecanoate. Our results show that SPME, when selecting the fibers to fit the polarity and volatility of the compounds, is an outstanding extraction method compared to purge and trap and methanol absorption, especially for a qualitative analysis. The best conditions for storing fibers exposed to compounds of high volatility were at low temperatures (6 degrees C) in sealed vials, while the worst way was to leave the exposed fiber unprotected at room temperature (22 degrees C). The dynamic sampling system was effectively tested on a fruiting body of a polypore fungus (Ganoderma applanatum) emitting 1-octen-3-ol, and again SPME showed to be the most sensitive technique.     

Evaluation of extracts and oils of tick-repellent plants from Sweden

Abstract. Leaves of Myrica gale Linnaeus (Myricaceae), Rhododendron tomentosum (Stokes) H. Harmaja (formerly Ledum palustre Linnaeus: Ericaceae) and Artemisia absinthium Linnaeus (Asteraceae) were extracted with organic solvents of different polarities and the essential oils of leaves were obtained by steam distillation. The extracts or oils were tested in the laboratory for repellency against host-seeking nymphs of Ixodes ricinus Linnaeus (Acari: Ixodidae). Rhododendron tomentosum oil, 10%, diluted in acetone, exhibited 95% repellency; R. tomentosum and A. absinthium extracts in ethyl acetate, > 70% repellency; A. absinthium extract in hexane, approximately 62% repellency; and M. gale oil, 10%, approximately 50% repellency on I. ricinus nymphs. Compounds in the leaf extracts or in the oils were collected by solid phase microextraction (SPME) and identified by gas chromatography-mass spectrometry (GC-MS) and/or MS. Characteristic volatiles detected from oil or extract of M. gale were the monoterpenes 1,8-cineole, alpha-terpineol, 4-terpineol and thujenol; and of R. tomentosum myrcene and palustrol. Characteristic volatiles from leaf extracts of A. absinthium were sabinene, oxygenated monoterpenes, e.g. thujenol and linalool, and geranyl acetate. Each plant species synthesized numerous volatiles known to exhibit acaricidal, insecticidal, 'pesticidal' and/or arthropod repellent properties. These plants may be useful sources of chemicals for the control of arthropods of medical, veterinary or agricultural importance.     

Olfactory receptor neurons in two Heliothine moth species responding selectively to aliphatic green leaf volatiles, aromatic compounds, monoterpenes and sesquiterpenes of plant origin

Moths of the subfamily Heliothinae are suitable models for comparative studies of plant odour information encoded by the olfactory system. Here we identify and functionally classify types of olfactory receptor neurons by means of electrophysiological recordings from single receptor neurons linked to gas chromatography and to mass spectrometry. The molecular receptive ranges of 14 types in the two polyphagous species Heliothis virescens and Helicoverpa armigera are presented. The receptor neurons are characterized by a narrow tuning, showing the best response to one primary odorant and weak responses to a few chemically related compounds. The most frequently occurring of the 14 types constituted the receptor neurons tuned to (+)-linalool, the enantioselectivity of which was shown by testing two samples with opposite enantiomeric ratios. These neurons, also responding to dihydrolinalool, were found to be functionally similar in the two related species. The primary odorants for 10 other receptor neuron types were identified as (3Z)-hexenyl acetate, (+)-3-carene, trans-pinocarveol, trans-verbenol, vinylbenzaldehyde, 2-phenylethanol, methyl benzoate, alpha-caryophyllene and caryophyllene oxide, respectively. Most odorants were present in several host and non-host plant species, often in trace amounts. The specificity as well as the co-localization of particular neuron types so far recorded in both species showed similarities of the olfactory systems receiving plant odour information in these two species of heliothine moths.     

Repellency of methyl jasmonate to <Emphasis Type="Italic">Ixodes ricinus</Emphasis> nymphs (Acari: Ixodidae)

In our search for tick repellents of plant origin, to be used as alternatives to commercial arthropod repellents, we investigated the effect of the well known plant signaling compound methyl jasmonate (MJ) using nymphs of the tick Ixodes ricinus. In laboratory tests, pieces of cloth with MJ at 0.075, 0.15, 0.30 and 0.75 mg/cm² yielded increasing repellencies against the nymphs: 57%, 71%, 92% and 99%, respectively, of the nymphs did not cling to the cloth. Repellency of MJ was also investigated in a tick-infested woodland area in central Sweden. Cotton flannel cloths sprayed with 0.05, 0.1 or 0.2 mg/cm² MJ dissolved in acetone were dragged over the ground vegetation. The numbers of nymphs on the treated cloths were significantly lower than those on the untreated cloth. Thus, MJ has, at the concentrations tested, significant repellent activity against I. ricinus nymphs.     

Analysis of copia sequence variation within and between Drosophila species

The sequences of the 5' long-terminal repeat (LTR) and adjacent leader regions of 27 full-length copia elements isolated from natural populations of Drosophila melanogaster, D. simulans, and D. mauritiana are presented. Phylogenetic analyses indicate that although D. melanogaster copia elements are distinct from those of D. simulans and D. mauritiana, the elements of these latter two species are not distinguishable from one another. LTRs and adjacent 5' leader regions of elements isolated from D. simulans and D. mauritiana are structurally similar to one another and carry substantial deletional variation mapping to regions previously identified as being of potential importance for copia expression.      

Aerobic degradation of a hydrocarbon mixture in natural uncontaminated potting soil by indigenous microorganisms at 20 °C and 6 °C

A hydrocarbon mixture containing p-xylene, naphthalene, Br-naphthalene and straight aliphatic hydrocarbons (C₁₄ to C₁₇) was aerobically degraded without lag phase by a natural uncontaminated potting soil at 20 °C and 6 °C. Starting concentrations were approximately 46 ppm for the aromatic and 13 ppm for the aliphatic compounds. All aliphatic hydrocarbons were degraded within 5 days at 20 °C, to levels below detection (ppb levels) but only down to 10% of initial concentration at 6 °C. Naphthalene was degraded within 12 days at 20 °C and unaffected at 6 °C. At 20 °C p-xylene was degraded within 20 days, but no degradation occurred at 6 °C. Br-naphthalene was only removed down to 30% of initial concentration at 20 °C, with no significant effect at 6 °C. The biodegradation was monitored with head space solid-phase microextraction and gas chromatography–mass spectrometry. Received: 5 October 1998 / Received revision: 4 December 1998 / Accepted: 5 December 1998     

Expression of Lex antigen in Schistosoma japonicum and S.haematobium and immune responses to Lex in infected animals: lack of Lex expression in other trematodes and nematodes

Adults of the human parasitic trematode Schistosoma mansoni, which causes hepatosplenic/intestinal complications in humans, synthesize glycoconjugates containing the Lewis x (Lex) Galbeta1-->4(Fucalpha1-- >3)GlcNAcbeta1-->R, but not sialyl Lewis x (sLex), antigen. We now report on our analyses of Lexand sLexexpression in S.haematobium and S.japonicum, which are two other major species of human schistosomes that cause disease, and the possible autoimmunity to these antigens in infected individuals. Antigen expression was evaluated by both ELISA and Western blot analyses of detergent extracts of parasites using monoclonal antibodies. Several high molecular weight glycoproteins in both S. haematobium and S. japonicum contain the Lexantigen, but no sialyl Lexantigen was detected. In addition, sera from humans and rodents infected with S.haematobium and S.japonicum contain antibodies reactive with Lex. These results led us to investigate whether Lexantigens are expressed in other helminths, including the parasitic trematode Fasciola hepatica , the parasitic nematode Dirofilaria immitis (dog heartworm), the ruminant nematode Haemonchus contortus , and the free-living nematode Caenorhabditis elegans . Neither Lexnor sialyl-Lexis detectable in these other helminths. Furthermore, none of the helminths, including schistosomes, express Lea, Leb, Ley, or the H- type 1 antigen. However, several glycoproteins from all helminths analyzed are bound by Lotus tetragonolobus agglutinin , which binds Fucalpha1-->3GlcNAc, and Wisteria floribunda agglutinin, which binds GalNAcbeta1-->4GlcNAc (lacdiNAc or LDN). Thus, schistosomes may be unique among helminths in expressing the Lexantigen, whereas many different helminths may express alpha1,3-fucosylated glycans and the LDN motif.