Identification, structure elucidation, and synthesis of volatile compounds in the exhaust gas of food factories

Our investigations deal with the identification and synthesis of volatile, odoriferous compounds contained in the exhaust gas of food factories and on the biodegradation of alkylpyrazines. Collection of odour emissions samples was performed with a gas sampler equipped with filter tubes containing the styrene-polymer SuperQ. After elution with solvents of different polarity, the extracts were analysed by GC/MS and chemical microreactions. Proposed structures were verified by comparison of analytical data with those of synthetic reference samples. Major components in the exhaust gas of a fat finishing factory were found to be aliphatic aldehydes, strongly dominated by hexanal. The identification of 1,2,3,3-tetramethylcyclohexene shows that for structural proof of target compounds the use of authentic reference samples is indispensable. In the exhaust gas from a chocolate factory, several carbonyl compounds and alkylated pyrazines could be identified. Biodegradation of the latter starts with hydrogenation at the nucleus.

Vittatalactone, a beta-lactone from the striped cucumber beetle, Acalymma vittatum

A novel beta-lactone, vittatalactone (1), was isolated from collections of airborne volatile compounds from feeding male striped cucumber beetles, Acalymma vittatum. The structure of 1 was determined to be (3R,4R)-3-methyl-4-(1,3,5,7-tetramethyloctyl)oxetan-2-one by microderivatization, GC-MS, and NMR studies. The absolute configurations at C-2 and C-3 on the beta-lactone ring were assigned by use of the modified Mosher method, applied to the beta-hydroxy acid methyl ester resulting from methanolysis of 1. Biological activity of 1, possibly as an aggregation pheromone for A. vittatum, was indicated by electrophysiological studies using beetle antennae and by the production of 1 by feeding male, and not female, beetles.

Identification of the sex pheromone of the currant shoot borer Lampronia capitella

Under an artificial light:dark cycle, females of Lampronia capitella were observed calling, with extended terminal abdominal segments, during the first 2 hr of the photoperiod. Extracts of terminal abdominal segments from females elicited large electroantennographic responses from male antennae. Gas chromatography with electroantennographic detection revealed three active peaks. Based on comparison of retention times and mass spectra of synthetic standards, these compounds were identified as (Z,Z)-9,11-tetradecadienol and the corresponding acetate and aldehyde. The electroantennographic activity of the four geometric isomers of all three compounds was investigated, and the respective (Z,Z)-isomer was found to be the most active in all cases. Aldehydes generally elicited larger antennal responses than alcohols, whereas acetates were the least active compounds. A subtractive trapping assay in the field, based on a 13:26:100 micrograms mixture of (Z,Z)-9,11-tetradecadienal, (Z,Z)-9,11-tetradecadienyl acetate, and (Z,Z)-9,11-tetradecadienol confirmed that all three compounds are pheromone components. Subtraction of (Z,Z)-9,11-tetradecadienol from the blend completely eliminated its attractiveness, whereas the other two-component blends showed reduced activity. This is the first pheromone identification from the monotrysian superfamily Incurvarioidea, confirming that the common pheromones among ditrysian moths (long-chain fatty acid derivatives comprising alcohols, acetates, and aldehydes with one or more double bonds) is not an autapomorphy of Ditrysia, but a synapomorphy of the more advanced heteroneuran lineages.

Does she smell like a queen? Chemoreception of a cuticular hydrocarbon signal in the ant Pachycondyla inversa

Primitive ant societies, with their relatively simple social structure, provide an opportunity to explore the evolution of chemical communication, in particular of mechanisms underlying within-colony discrimination. In the same colony, slight differences in individual odours can be the basis for discrimination between different castes, classes of age and social status. There is some evidence from correlative studies that such inter-individual variation is associated with differences in reproductive status, but direct proof that certain chemical compounds are detected and recognized by ants is still lacking. In the ponerine ant Pachycondyla inversa, fertile queens and, in orphaned colonies, dominant egg-laying workers are characterized by the predominance of a branched hydrocarbon, 3,11-dimethylheptacosane (3,11-diMeC(27)) on the cuticle. Using electroanntennography and gas chromatography with electroantennographic detection, we show that the antennae of P. inversa workers react to this key compound. 3,11-diMeC(27) is correlated with ovarian activity and, because it is detected, is likely to assume the role of a fertility signal reflecting the quality of the sender.

Enantioselectivity of projection neurons innervating identified olfactory glomeruli

Projection neurons (PNs) with arborizations in the sexually dimorphic "lateral large female glomerulus" (latLFG) in the antennal lobe (AL) of the moth Manduca sexta previously were shown to respond preferentially to antennal stimulation with (+/-)linalool, a volatile compound commonly emitted by plants. In the present study, using intracellular recording and staining techniques, we examined the responsiveness of latLFG-PNs to the enantiomers, (+)linalool and (-)linalool and found that (1) latLFG-PNs are more responsive to antennal stimulation with (+)linalool than with (-)linalool, (2) PNs with arborizations in a glomerulus adjacent to the latLFG are preferentially responsive to (-)linalool, and (3) PNs with arborizations confined to other glomeruli near the latLFG are equally responsive to both enantiomers of linalool. Structure-activity studies showed that the hydroxyl group in this tertiary terpene alcohol is the key feature of the molecule determining the response of enantioselective PNs to linalool. In contrast, the responses of non-enantioselective PNs are less dependent on the alcoholic functionality of linalool. Our findings show that PNs innervating a uniquely identifiable glomerulus respond preferentially to a particular enantiomer of an odor substance. Moreover, PNs with arborizations in a glomerulus adjacent to the latLFG, although less sensitive than latLFG-PNs to linalool, respond preferentially to the opposite enantiomer, demonstrating that information about stimulus-absolute configuration can be encoded in different olfactory glomeruli.

A Stingless Bee (Melipona seminigra) Marks Food Sources with a Pheromone from Its Claw Retractor Tendons

By depositing scent marks on flowers, bees reduce both the search time and the time spent with the handling of nonrewarding flowers. They thereby improve the efficiency of foraging. Whereas in honey bees the source of these scent marks is unknown, it is assumed to be the tarsal glands in bumble bees. According to histological studies, however, the tarsal glands lack any openings to the outside. Foragers of the stingless bee Melipona seminigra have previously been shown to deposit an attractant pheromone at sugar solution feeders, which is secreted at the tips of their tarsi. Here we show that the claw retractor tendons have specialized glandular epithelia within the femur and tibia of all legs that produce this pheromone. The secretion accumulates within the hollow tendon, which also serves as the duct to the outside, and is released from an opening at the base of the unguitractor plate. In choice experiments, M. seminigra was attracted by feeders baited with pentane extracts of the claw retractor tendons in the same way as it was attracted by feeders previously scent marked by foragers. Our results resolve the seeming contradiction between the importance of foot print secretions and the lack of openings of the tarsal glands.

Sex pheromone of the leaf-miner Phyllonorycter platani: (Z10)-tetradecenyl acetate

A female produced sex pheromone of the leaf-miner pest Phyllonorycter platani (Staudinger) (Lepidoptera: Gracillariidae) was identified as (Z10)-tetradecenyl acetate. Field trapping trials confirmed activity of this compound. The presence of the geometrical isomer (E10)-tetradecenyl acetate, a pheromone component of other Phyllonorycter species, reduced trap efficacy.

Cuticular Hydrocarbons and Aggression in the Termite Macrotermes Subhyalinus

Cuticular hydrocarbons are among the prime candidates for nestmate recognition in social insects. We analyzed the variation of cuticular hydrocarbons in the termite species M. subhyalinus in West Africa (Comoë National Park) on a small spatial scale (< 1 km). We found considerable variation in the composition of cuticular hydrocarbons among colonies, with four distinct chemical phenotypes. Different phenotypes occurred within each of the four habitats. The difference between these phenotypes is primarily due to unsaturated compounds. A clear correlation between the difference of the hydrocarbon composition and the aggression between colonies was found. This correlation also holds in a multivariate analysis of genetic similarity (measured by AFLPs), morphometric distances (measured by Mahalanobis-distances). as well as geographic distances between colonies. In a more detailed analysis of the correlation between the composition of cuticular hydrocarbons and aggression, we found that no single compound is sufficient to explain variation in aggression between pairings of colonies. Thus, termites seem to use a bouquet of compounds. Multiple regression analysis suggested that many of these compounds are unsaturated hydrocarbons and, thus, may play a key role in colony recognition.

The chemistry of sexual deception in an orchid-wasp pollination system

The "sexually deceptive" orchid Chiloglottis trapeziformis attracts males of its pollinator species, the thynnine wasp Neozeleboria cryptoides, by emitting a unique volatile compound, 2-ethyl-5-propylcyclohexan-1,3-dione, which is also produced by female wasps as a male-attracting sex pheromone.

Do social parasitic bumblebees use chemical weapons? (Hymenoptera, Apidae)

The bumblebee Bombus (Psithyrus) norvegicus Sp.-Schn. is an obligate social parasite of B. (Pyrobombus) hypnorum L. Behavioural observations indicated that nest-invading B. norvegicus females may use allomones to defend themselves against attacking host workers. However, so far no defensive chemicals used by social parasitic bumblebee females have been identified. We analysed volatile constituents of the cuticular lipid profile of B. norvegicus females. Furthermore, we performed electrophysiological studies and behavioural experiments in order to identify possible chemical weapons. Coupled gas chromatography-electroantennography showed 15 compounds to trigger responses in antennae of the host workers. Using gas chromatography-mass spectrometry, the main compound among the cuticular volatiles of B. norvegicus females was found to be dodecyl acetate. A corresponding mixture of synthetic volatiles as well as pure dodecyl acetate showed a strong repellent effect on starved host workers. B. norvegicus females use dodecyl acetate to repel attacking B. hypnorum workers during nest usurpation and subsequently during colony development. Dodecyl acetate is the first repellent allomone identified in bumblebees.

Frontalin: De novo biosynthesis of an aggregation pheromone component by Dendroctonus spp. bark beetles (Coleoptera: Scolytidae)

The pheromone component, frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane) is thought to be formed in Dendroctonus spp. bark beetles through the cyclization of oxygenated 6-methyl-6-hepten-2-one (6-MHO). Unlike many of the isoprenoid pheromone components of bark beetles, there is no obvious immediate host conifer precursor for 6-MHO or frontalin. To elucidate the biosynthetic pathway of frontalin, juvenile hormone-treated male Dendroctonus jeffreyi were injected separately with [1-(14)C]acetate, [2-(14)C]mevalonolactone, [1-(14)C]isopentenol, [1-(14)C]:[1-(3)H]isopentenol, and [4,5-(3)H]leucine. Subsequently volatiles were collected on Porapak Q from these males and abdominal tissues were extracted. Radio-HPLC analyses of extracts from males injected with each radiolabeled substrate showed that radioactivity from the injected precursors eluted in a peak with a retention time that matches that of unlabeled frontalin. In all cases, HPLC fractions containing radiolabel that eluted at the same time as a frontalin standard were analyzed by GC-FID and GC-MS to confirm the presence of frontalin. In a separate study, male D. jeffreyi were injected with [1-(13)C]acetate and an abdominal tissue extract from these insects was analyzed by tandem gas chromatography-isotope ratio monitoring-mass spectrometry (GC-IRM-MS), which unequivocally showed incorporation of (13)C into frontalin. Because mevalonate is the key intermediate in the isoprenoid pathway, its incorporation (as mevalonolactone) into frontalin provides compelling evidence that the biosynthesis of frontalin involves that pathway in some form. In the experiment with [1-(14)C]:[1-(3)H]isopentenol, there was no significant difference in the mean percentage incorporation of either radioisotope into frontalin. This supports the role of the classical isoprenoid pathway, as tritium would be lost if only a hybrid pathway were involved. Confirming that de novo synthesis may be general to all Dendroctonus spp., (14)C-acetate was also incorporated into frontalin by females of D. rufipennis and D. simplex. A radiolabeled precursor/pathway inhibitor study showed that the fatty acid synthase inhibitor, 2-octynoic acid, increased (although not significantly) the mass of frontalin produced and significantly increased the percentage incorporation of radioactivity from [1-(14)C]acetate into frontalin. This suggests that as fatty acid biosynthesis is blocked, an increased amount of acetate is funneled into frontalin production via the isoprenoid pathway.

(R)-acetoin-female sex pheromone of the summer chafer Amphimallon solstitiale (L.)

Extracts of Amphimallon solstitiale (L.), a well known, widely distributed and rather common European scarab beetle, were analyzed by GC-MS and GC-EAD. Acetoin - (R):(S) > 9:1 - as well as 2,3-butanediol - (2R,3R): (2S,3S):meso = 1:1:9 - were present in extracts of both males and females. Although (2S,3S)-butanediol did not show any EAD activity, the other compounds elicited strong responses exclusively with male antennae. In contrast, several EAD active green leaf volatiles were detected equally well by male and female antennae. During preliminary field bioassays, (R)-acetoin was highly attractive to swarming males, whereas neither rac-acetoin nor the 2,3-butanediols showed activity. Therefore, (R)-acetoin is the female sex pheromone of A. solstitiale.

Identification of pheromones and optimization of bait composition for click beetle pests (Coleoptera: Elateridae) in Central and Western Europe

Based on analysis of pheromone gland extracts, highly attractive new baits have been developed for three click beetle pests. That for Agriotes brevis is a mixture of geranyl butanoate and (E,E)-farnesyl butanoate, and that for A rufipalpis and A sordidus contains geranyl hexanoate alone. From known data from species populating Russia, optimized bait compositions for species in Central and Western Europe were developed as follows: geranyl octanoate + geranyl butanoate for A lineatus, geranyl isovalerate for A litigiosus, geranyl hexanoate + geranyl octanoate for A obscurus, geranyl butanoate alone for A sputator and (E,E)-farnesyl acetate alone for A ustulatus. Although slight differences were found in gland contents with A litigiosus var laichartingi and fenotypus typicus, nevertheless there were no differences in response to the optimum bait. There were no differences in pheromone composition or response to the optimized bait between the two morphological forms ('black' and 'red') of A ustulatus. As a result of these studies, highly effective pheromone baits are now available for monitoring and population reduction in all important pest click beetle species in Central and Western Europe.

A novel sex-specific and inducible monoterpene synthase activity associated with a pine bark beetle, the pine engraver, Ips pini

Ecological interactions of conifers and coniferophagous bark beetles are determined in part by terpenoids (isoprenoids), which are major defense metabolites of conifer oleoresin. Curiously, similar compounds are important aggregation pheromones of conifer-attacking bark beetles. Terpene synthases are responsible for generating the enormous variety of terpenoid carbon skeletons found in nature. These catalysts convert short-chain prenyl diphosphates to a diverse assortment of hemiterpene, monoterpene, sesquiterpene, and diterpene natural products. While terpene synthases have frequently been characterized from plant and microbial sources, they have not yet been described in animals. Here we report the discovery of a monoterpene synthase activity in an insect, the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae). Cell-free assays of I. pini revealed that geranyl diphosphate (GDP) is converted to the acyclic monoterpene myrcene in whole-body extracts from males, but not females. Furthermore, the monoterpene synthase activity in males can be induced by prior treatment with juvenile hormone III (JH III) or by feeding on phloem from the host trees, Jeffrey pine (Pinus jeffreyi Grev. & Balf.) or red pine (Pinus resinosa Ait.). The sex-specificity and endocrine induction of this activity argue for its involvement in the biosynthesis of monoterpenoid pheromones mediated by enzymes from insect tissue. This discovery is the first example of a monoterpene synthase in the Metazoa and evokes exciting new questions about the origin, evolution, and occurrence of terpene synthases.

Pollinator attraction in a sexually deceptive orchid by means of unconventional chemicals

Ophrys flowers mimic virgin females of their pollinators, and thereby attract males for pollination. Stimulated by scent, the males attempt to copulate with flower labella and thereby ensure pollination. Here, we show for the first time, to our knowledge, that pollinator attraction in sexually deceptive orchids may be based on a few specific chemical compounds. Ophrys speculum flowers produce many volatiles, including trace amounts of (omega-1)-hydroxy and (omega-1)-oxo acids, especially 9-hydroxydecanoic acid. These compounds, which are novel in plants, prove to be the major components of the female sex pheromone in the scoliid wasp Campsoscolia ciliata, and stimulate male copulatory behaviour in this pollinator species. The specificity of the signal depends primarily on the structure and enantiomeric composition of the oxygenated acids, which is the same in wasps and in the orchids. The overall composition of the blend differs significantly between the orchid and its pollinator and is of secondary importance. 9-Hydroxydecanoic acid is a rarely occurring compound that until now has been identified only in honeybees. Contrary to the standard hypothesis that Ophrys flowers produce only 'second-class attractivity compounds' and are neglected once the pollinator females are present, we show that flowers are more attractive to the males than are their own females.

Characteristic odor of Osmoderma eremita identified as a male-released pheromone

Osmoderma eremita (Scopoli) is an endangered scarab beetle living in hollow trees. It has mainly been known for its characteristic odor, typically described as a fruity, peachlike or plumlike aroma. The odor emanating from a single beetle can sometimes be perceived from a distance of several meters. In this paper, we show that the characteristic odor from O. eremita is caused by the compound (R)-(+)-gamma-decalactone, released in large quantities mainly or exclusively by male beetles. Antennae from male and female beetles responded in a similar way to (R)-(+)-gamma-decalactone in electroantennographic recordings. Field trapping experiments showed that (R)-(+)-gamma-decalactone is a pheromone attracting female beetles. Lactones similar to (R)-(+)-gamma-decalactone are frequently used as female-released sex pheromones by phytophagous scarabs. This is, however, the first evidence of a lactone used as a male-produced pheromone in scarab beetles. We propose that the strong signal from males is a sexually selected trait used to compete for females and matings. The signal could work within trees but also act as a guide to tree hollows, which are an essential resource for O. eremita. Males may, thus, attract females dispersing from their natal tree by advertising a suitable habitat. This signal could also be exploited by other males searching for tree hollows or for females, which would explain the catch of several males in our traps.

(S)-(+)-linalool, a mate attractant pheromone component in the bee Colletes cunicularius

Enantiomerically pure (S)-(+)-linalool was the main constituent in the extracts of the cephalic secretions of virgin females, mated females, freshly emerged males, and patrolling males of the solitary bee Colletes cunicularius. After copulation, the content of (S)-(+)-linalool emitted by the female was strongly reduced. Electrophysiological experiments revealed that both enantiomers of linalool elicited responses from the antennae of the males. Field tests using the pure enantiomers and the racemate of linalool showed that the number of male bees attracted was highest for (S)-(+)-linalool. The search flight activity in the mating flight area increased dramatically when patrolling males were presented with (S)-(+)-linalool vs (R)-(-)-linalool. Taken together, these data indicate a mate attractant pheromone function of (S)-(+)-linalool.