Semiochemicals produced by fungal bark beetle symbiont Endoconidiophora rufipennis and the discovery of an anti-attractant for Ips typographus

Bark beetles vector symbiotic fungal species into their host trees during mass attacks. The symbiotic relationship with blue stain fungi of the Ascomycetes, including genera of Endoconidiophora (syn. = Ceratocystis), promotes successful establishment whereby the microbes help to overcome the host trees' defence and degrade toxic resins. This is the first study to evaluate both the volatile emissions from an insect-associated blue stain fungus over time and the insect response in a field trapping experiment. Volatile emissions from isolates of Endoconidiophora rufipennis (ER) were collected by solid-phase microextraction (SPME) and analysed by gas chromatography-mass spectroscopy (GC-MS) over a period of 30 days. This virulent North American fungus is closely related to E. polonica, a symbiotic fungus known from Eurasian spruce bark beetle Ips typographus.Nine volatiles were emitted by ER in substantial amounts: isoamyl acetate, sulcatone, 2-phenethyl acetate, geranyl acetone, geranyl acetate, citronellyl acetate, (R)- and (S)-sulcatol, and (R)-sulcatol acetate. A late peaking compound was geranyl acetone. In the field trapping experiment, three of the fungal volatiles (geranyl acetone, 2-phenethyl acetate and sulcatone) were tested in combination with a synthetic aggregation pheromone for I. typographus. Traps with geranyl acetone attracted lower numbers of I. typographus compared to traps with 2-phenethyl acetate, sulcatone or the pheromone alone as a control. The results showed that geranyl acetone acts as an anti-attractant and may act naturally on I. typographus as a cue from an associated fungus to signal an overexploited host.

The human odorant receptor OR10A6 is tuned to the pheromone of the commensal fruit fly Drosophila melanogaster

All living things speak chemistry. The challenge is to reveal the vocabulary, the odorants that enable communication across phylogenies and to translate them to physiological, behavioral, and ecological function. Olfactory receptors (ORs) interface animals with airborne odorants. Expression in heterologous cells makes it possible to interrogate single ORs and to identify cognate ligands. The cosmopolitan, anthropophilic strain of the vinegar fly Drosophila melanogaster depends on human resources and housing for survival. Curiously, humans sense the pheromone (Z)-4-undecenal (Z4-11Al) released by single fly females. A screening of all human ORs shows that the most highly expressed OR10A6 is tuned to Z4-11Al. Females of an ancestral African fly strain release a blend of Z4-11Al and Z4-9Al that produces a different aroma, which is how we distinguish these fly strains by nose. That flies and humans sense Z4-11Al via dedicated ORs shows how convergent evolution shapes communication channels between vertebrate and invertebrate animals.

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Humans sense the sex pheromone Z411-Al released by single Drosophila melanogaster females

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The most highly expressed human olfactory receptor OR10A6 is tuned to Z411-Al

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An African fly strain emits two aldehydes, which we distinguish from Z411-Al by nose

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Convergent evolution shapes chemical communication between phylogenies

The female sex pheromone (Z)-4-undecenal mediates flight attraction and courtship in Drosophila melanogaster

Specific mate communication and recognition underlies reproduction and hence speciation. Our study provides new insights in Drosophila melanogaster premating olfactory communication. Mate communication evolves during adaptation to ecological niches and makes use of social signals and habitat cues. Female-produced, species-specific volatile pheromone (Z)-4-undecenal (Z4-11Al) and male pheromone (Z)-11-octadecenyl acetate (cVA) interact with food odour in a sex-specific manner. Furthermore, Z4-11Al, which mediates upwind flight attraction in both sexes, also elicits courtship in experienced males. Two isoforms of the olfactory receptor Or69a are co-expressed in the same olfactory sensory neurons. Z4-11Al is perceived via Or69aB, while the food odorant (R)-linalool is a main ligand for the other variant, Or69aA. However, only Z4-11Al mediates courtship in experienced males, not (R)-linalool. Behavioural discrimination is reflected by calcium imaging of the antennal lobe, showing distinct glomerular activation patterns by these two compounds. Male sex pheromone cVA is known to affect male and female courtship at close range, but does not elicit upwind flight attraction as a single compound, in contrast to Z4-11Al. A blend of the food odour vinegar and cVA attracted females, while a blend of vinegar and female pheromone Z4-11Al attracted males, instead. Sex-specific upwind flight attraction to blends of food volatiles and male and female pheromone, respectively, adds a new element to Drosophila olfactory premating communication and is an unambiguous paradigm for identifying the behaviourally active components, towards a more complete concept of food-pheromone odour objects.

Stereochemistry of two pheromonal components of the bumblebee wax moth, Aphomia sociella

The bumblebee wax moth, Aphomia sociella, is a parasite of bumblebees. In this species, males produce sexual pheromone to attract females, while females produce an aphrodisiac pheromone that initiates male courtship. Both pheromones contain 6,10,14-trimethylpentadecan-2-one (TMPD-one) and the corresponding alcohol, 6,10,14-trimethylpentadecan-2-ol (TMPD-ol) in sex specific quantities. Male sex pheromone consists of 7 components with TMPD-one as a minor one and traces of TMPD-ol. In female aphrodisiac pheromone, TMPD-ol is the major component, while TMPD-one is present in traces. Here we report on the absolute configuration of TMPD-one in male sex pheromone and TMPD-ol in female aphrodisiac pheromone of A. sociella. The configuration was determined from GC/MS of prepared (S)-acetoxypropionyl esters of TMPD-ol. TMPD-one was first reduced to the alcohol that was then derivatized with (S)-acetoxypropionyl chloride. The GC/MS data of obtained diastereoisomers were compared with synthetic standards. The absolute configuration of TMPD-one in the male pheromone was (6R,10R). The configuration of TMPD-ol in the female pheromone was (2R,6R,10R). Electrophysiological experiments showed that TMPD-one and TMPD-ol are perceived by both sexes. The synthetic standards of naturally produced stereoisomers elicited higher responses than mixtures of all stereoisomers.

Identification and Field Assay of Two Aggregation Pheromone Components Emitted by Males of the Bark Beetle Polygraphus punctifrons (Coleoptera: Curculionidae)

The bark beetle Polygraphus punctifrons (Coleoptera: Curculionidae) is a species that feeds on Norway spruce (Picea abies) and is found in the Northern parts of Europe and Russia. The release of volatile organic compounds (VOCs) produced by males and females of P. punctifrons when the beetles bore into spruce stem sections in a laboratory environment was studied using solid phase microextraction (SPME). The sampled VOCs emitted by boring beetles were analysed by gas chromatography and mass spectrometry (GCMS). (+)-2-[(1R,2S)-1-Methyl-2-(prop-1-en-2-yl)cyclobutyl]ethanol [(+)-(1R,2S)-grandisol] and (-)-(R)-1-isopropyl-4-methyl-3-cyclohexen-1-ol [(-)-(R)-terpinen-4-ol] were identified to be male specific volatiles. The identity of the compounds was confirmed by comparison with synthetic samples. Field trials with synthetic compounds in Sweden showed that racemic grandisol per se was strongly attractive for both males and females, while (-)-(R)-terpinen-4-ol was not. Further, when adding (-)-(R)-terpinen-4-ol to rac-grandisol, a synergistic effect was observed as the trap catch of P. punctifrons was fourfold. (-)-(R)-Terpinen-4-ol by its own did not attract P. punctifrons but Polygraphus poligraphus, and the latter was also attracted to traps baited with a 10:90 mixture of the two compounds. Thus, we have identified (+)-(1R,2S)-grandisol as a main component and (-)-(R)-terpinen-4-ol as a minor component of the aggregation pheromone of P. punctifrons. This opens future possibilities to monitor and, if necessary, manage populations of P. punctifrons.

The Scent of the Fly

(Z)-4-undecenal (Z4-11Al) is the volatile pheromone produced by females of the vinegar fly Drosophila melanogaster. Female flies emit Z4-11Al for species-specific communication and mate-finding. A sensory panel finds that synthetic Z4-11Al has a characteristic flavour, which can be perceived even at the small amounts produced by a single female fly. Since only females produce Z4-11Al, and not males, we can reliably distinguish between single D. melanogaster males and females, according to their scent. Females release Z4-11Al at 2.4 ng/h and we readily sense 1 ng synthetic Z4-11Al in a glass of wine (0.03 nmol/L), while a tenfold concentration is perceived as a loud off-flavour. This corroborates the observation that a glass of wine is spoilt by a single D. melanogaster fly falling into it, which we here show is caused by Z4-11Al. The biological role of Z4-11Al or structurally related aldehydes in humans and the basis for this semiochemical convergence remains yet unclear.

A Drosophila female pheromone elicits species-specific long-range attraction via an olfactory channel with dual specificity for sex and food

Background

Mate finding and recognition in animals evolves during niche adaptation and involves social signals and habitat cues. Drosophila melanogaster and related species are known to be attracted to fermenting fruit for feeding and egg-laying, which poses the question of whether species-specific fly odours contribute to long-range premating communication.

Results

We have discovered an olfactory channel in D. melanogaster with a dual affinity to sex and food odorants. Female flies release a pheromone, (Z)-4-undecenal (Z4-11Al), that elicits flight attraction in both sexes. Its biosynthetic precursor is the cuticular hydrocarbon (Z,Z)-7,11-heptacosadiene (7,11-HD), which is known to afford reproductive isolation between the sibling species D. melanogaster and D. simulans during courtship. Twin olfactory receptors, Or69aB and Or69aA, are tuned to Z4-11Al and food odorants, respectively. They are co-expressed in the same olfactory sensory neurons, and feed into a neural circuit mediating species-specific, long-range communication; however, the close relative D. simulans, which shares food resources with D. melanogaster, does not respond to Z4-11Al.

Conclusion

The Or69aA and Or69aB isoforms have adopted dual olfactory traits. The underlying gene yields a collaboration between natural and sexual selection, which has the potential to drive speciation.

(Z)-3-Dodecenoic acid is the main component of full-body n-hexane extracts from two Acacia gall-inducing thrips (Thysanoptera) and may function as an alarm pheromone

A major interest in the gall-inducing thrips of Australia began with the discovery that some species have eusocial colonies. The origin of social castes remains one of the outstanding questions in evolutionary biology. The inference of the ancestral stage from study of solitary species is important to understanding the evolutionary history of semiochemicals in social species. Here we investigated two solitary species, Kladothrips nicolsoni and K. rugosus. Whole body extracts revealed that (Z)-3-dodecenoic acid, here reported for the first time in a thrips species, is the main component. (Z)-3-Dodecenoic acid and (E)-3-dodecenoic acid were synthesized in high stereoisomeric purity (> 99.8%) and exposed to K. nicolsoni 2nd-instar larvae in a contact chemoreception bioassay to test for potential bioactivity. Both isomers decreased the average time spent in the treated area per entry suggesting repellence at the tested dose. (Z)-3-Dodecenoic acid may function as alarm pheromone. (E)-3-Dodecenoic acid increased also the absolute change in direction of larvae compared to an n-hexane control and could potentially function as a repellent.

Cracking the olfactory code of a butterfly: the scent of ageing

Although olfaction is a primary mode of communication, its importance in sexual selection remains understudied. Here, using the butterfly Bicyclus anynana, we address all the parameters of importance to sexual selection for a male olfactory signal. We show that variation in the male sex pheromone composition indicates male identity and male age. Courting males of different ages display small absolute (c. 200 ng) but large relative (100%) change of one specific pheromone component (hexadecanal) which, unlike the other components, showed no heritability. Females prefer to mate with mid-aged over younger males and the pheromone composition is sufficient to determine this preference. Surprisingly refined information is thus present in the male olfactory signal and is used for sexual selection. Our data also reveal that there may be no 'lek paradox' to resolve once the precise signal of importance to females is identified, as hexadecanal is, as expected, depleted in additive genetic variation.

Alarm pheromones and chemical communication in nymphs of the tropical bed bug Cimex hemipterus (Hemiptera: Cimicidae)

The recent resurge of bed bug infestations (Cimex spp.; Cimicidae) and their resistance to commonly used pesticides calls for alternative methods of control. Pheromones play an important role in environmentally sustainable methods for the management of many pest insects and may therefore be applicable for the control of bed bugs. The tropical bed bug, Cimex hemipterus, is a temporary ectoparasite on humans and causes severe discomfort. Compared to the common bed bug, Cimex lectularius, little is known about the chemical signalling and pheromone-based behaviour of the tropical species. Here, we show that the antennal morphology and volatile emission of C. hemipterus closely resembles those of C. lectularius and we test their behavioural responses to conspecific odour emissions. Two major volatiles are emitted by male, female and nymph C. hemipterus under stress, (E)-2-hexenal and (E)-2-octenal. Notably, nymph emissions show contrasting ratios of these compounds to adults and are further characterized by the addition of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal. The discovery of this nymph pheromone in C. hemipterus is potentially the cause of a repellent effect observed in the bio-tests, where nymph odours induce a significantly stronger repellent reaction in conspecifics than adult odours. Our results suggest that pheromone-based pest control methods developed for C. lectularius could be applicable to C. hemipterus, with the unique nymph blend showing promising practical properties.

(6R, 10R)-6,10,14-trimethylpentadecan-2-one, a dominant and behaviorally active component in male orchid bee fragrances

6,10,14-Trimethylpentadecan-2-one (Hexahydrofarnesyl acetone; HHA) previously has been found to be a major component in tibial fragrances of male orchid bees, Euglossa spp. HHA is a chiral molecule with four possible stereoisomers, (6R, 10R)-, (6R, 10S)-, (6S, 10R)-, and (6S, 10S)-6,10,14-trimethylpentadecan-2-one. In the present study, we characterized HHA extracted from Euglossa as the pure enantiomer (6R, 10R)-6,10,14-trimethylpentadecan-2-one. During bioassays in Mexico and Panama, the synthetic RR-isomer attracted males of six species of orchid bees, including three that were known to contain HHA in their tibial fragrances. Possible sources of HHA for wild bees are flowers of euglossophilous orchids and aroids. With a molecular weight of 268, HHA is the largest natural molecule known to attract male orchid bees in pure form. Its attractiveness to males suggests that low-volatility compounds have a function in male signals, e.g., serve as a "base note" in complex odor bouquets.

Synthesis of 2-(2-aminopyrimidine)-2,2-difluoroethanols as potential bioisosters of salicylidene acylhydrazides

Salicylidene acylhydrazides are inhibitors of type III secretion in several Gram-negative pathogens. To further develop the salicylidene acylhydrazides, scaffold hopping was applied to replace the core fragment of the compounds. The novel 2-(2-amino-pyrimidine)-2,2-difluoroethanol scaffold was identified as a possible analog to the salicylidene acylhydrazide core structure. The synthesis of a library of 2-(2-amino-pyrimidine)-2,2-difluoro-ethanols is described in this paper.

RNA polymerases from avian liver. Isolation and fractionation by heparin-sepharose chromatography

Optimal conditions for isolation of rooster liver nuclei were studied for the purification of RNA polymerases I and II by varying the concentrations of sucrose, magnesium chloride and spermine in the isolation medium. Addition of spermine and/or magnesium chloride to the hypertonic sucrose medium was found to be advantageous for the purification. Heparin-Sepharose chromatography can be recommended for purification of RNA polymerases when used in a stepwise manner. Furthermore, gradient elution in the heparin-Sepharose chromatography was found to separate RNA polymerases I and II. RNA polymerase III was eluted with RNA polymerase I. A few minor peaks of RNA polymerase II activity were detected with gradient elution. Factors influencing the affinity of RNA polymerases towards heparin-Sepharose are discussed.