Tetranorsesquiterpenoids as Attractants of Yucca Moths to Yucca Flowers.

The obligate pollination mutualism between Yucca and yucca moths is a classical example of coevolution. Oviposition and active pollination by female yucca moths occur at night when Yucca flowers are open and strongly scented. Thus, floral volatiles have been suggested as key sensory signals attracting yucca moths to their host plants, but no bioactive compounds have yet been identified. In this study, we showed that both sexes of the pollinator moth Tegeticula yuccasella are attracted to the floral scent of the host Yucca filamentosa. Chemical analysis of the floral headspace from six Yucca species in sections Chaenocarpa and Sarcocarpa revealed a set of novel tetranorsesquiterpenoids putatively derived from (E)-4,8-dimethyl-1,3,7-nonatriene. Their structure elucidation was accomplished by NMR analysis of the crude floral scent sample of Yucca treculeana along with GC/MS analysis and confirmed by total synthesis. Since all these volatiles are included in the floral scent of Y. filamentosa, which has been an important model species for understanding the pollination mutualism, we name these compounds filamentolide, filamentol, filamental, and filamentone. Several of these compounds elicited antennal responses in pollinating (Tegeticula) and non-pollinating (Prodoxus) moth species upon stimulation in electrophysiological recordings. In addition, synthetic (Z)-filamentolide attracted significant numbers of both sexes of two associated Prodoxus species in a field trapping experiment. Highly specialized insect-plant interactions, such as obligate pollination mutualisms, are predicted to be maintained through "private channels" dictated by specific compounds. The identification of novel bioactive tetranorsesquiterpenoids is a first step in testing such a hypothesis in the Yucca-yucca moth interaction.

The Pattern of Straight Chain Hydrocarbons Released by Yucca Flowers (Asparagaceae).

The hydrocarbon pattern in the floral scent of Yucca species was found to comprise a group of unbranched, mid-chain alkanes, alkenes, and an alkadiene. In Y. reverchonii, highly dominant (Z)-8-heptadecene is accompanied by (6Z,9Z)-6,9-heptadecadiene and heptadecane as minor components and by traces of other saturated and unsaturated hydrocarbons with similar chain length. Some of these volatiles proved to be perceived by the antennae of Tegeticula cassandra (pollinating seed-eater of Yucca) and Prodoxus decipiens (herbivore on Yucca). The possible biosynthesis of the compounds is discussed.

Evidence that Cerambycid Beetles Mimic Vespid Wasps in Odor as well as Appearance.

We present evidence that cerambycid species that are supposed mimics of vespid wasps also mimic their model's odor by producing spiroacetals, common constituents of vespid alarm pheromones. Adults of the North American cerambycids Megacyllene caryae (Gahan) and Megacyllene robiniae (Forster) are conspicuously patterned yellow and black, and are believed to be mimics of aculeate Hymenoptera, such as species of Vespula and Polistes. Adult males of M. caryae produce an aggregation-sex pheromone, but both sexes produce a pungent odor when handled, which has been assumed to be a defensive response. Headspace aerations of agitated females of M. caryae contained 16 compounds with mass spectra characteristic of spiroacetals of eight distinct chemical structures, with the dominant compound being (7E,2E)-7-ethyl-2-methyl-1,6-dioxaspiro[4.5]decane. Headspace samples of agitated males of M. caryae contained five of the same components, with the same dominant compound. Females of M. robiniae produced six different spiroacetals, one of which was not produced by M. caryae, (2E,7E)-2-ethyl-7-methyl-1,6-dioxaspiro[4.5]decane, and five that were shared with M. caryae, including the dominant (2E,8E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. The latter compound is the sole spiroacetal produced by both males and females of a South American cerambycid species, Callisphyris apicicornis (Fairmaire & Germain), which is also thought to be a wasp mimic. Preliminary work also identified spiroacetals of similar or identical structure released by vespid wasps that co-occur with the Megacyllene species.

Acyclic sesquiterpenes released by Candida albicans inhibit growth of dermatophytes.

It is unresolved as to whether fungi that share a common skin habitat might in principal interact. In in vitro screening tests with Candida albicans, Trichophytum rubrum and other common dermatophytes, we found C. albicans releases volatile compounds that inhibit growth of the dermatophytes. By applying (enantioselective) gas chromatography combined with mass spectrometry we identified 8 compounds among which stereochemically pure (3R,6E)-2,3-dihydrofarnesol (R-DHF) and (2E,6E)-farnesol (F-ol) were the main components. Synthetic R-DHF and its enantiomer, (3S,6E)-2,3-dihydrofarnesol (S-DHF), as well as F-ol were tested for their capacity to inhibit growth of dermatophytes in microtiter-plate assays over 62 h. All three compounds showed significant and concentration-dependent, to a certain extent even species-specific, inhibitory effects on T. rubrum, T. mentagrophytes, Microsporum canis and Epidermophyton floccosum. In general, S-DHF and F-ol had a pronounced effect on the dermatophytes, similar to or even stronger than that of fluconazole. E. floccosum was completely suppressed by 12.5 µg/ml dihydrofarnesol, as was the inhibition caused by 50 µg/ml fluconazole. Similarly, S-DHF- was more active against T. rubrum than fluconazole. To the best of our knowledge, 2,3-dihydrofarnesol has not yet been described as a volatile generated by microorganisms, and its inhibitory effect on dermatophytes is new to science. However, the relevance of this compound in interfungal interference in situ is unknown. In contrast, farnesol is a well-known semiochemical of C. albicans with intraspecific effects and a clear impact on other microorganisms. Mutual intermicrobial communication based on fungal volatiles therefore appears to be an exciting field for future investigations.

Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae).

Females of the parasitoid wasp Trichogramma turkestanica produce the putative polydeoxypropionates (2E,4E,6S,8S,10S)-4,6,8,10-tetramethyltrideca-2,4-diene and (2E,4E,6S,8S,10S)-4,6,8,10-tetramethyltrideca-2,4-dien-1-ol or their enantiomers as sex specific volatiles. The structures were assigned on the basis of GC-MS investigations using synthetic reference compounds.

Identification of the female-produced sex pheromone of Tischeria ekebladella, an oak leafmining moth.

The native leafmining moth Tischeria ekebladella (Lepidoptera: Tischeriidae) feeds on oaks and recently has become a pest of silviculture and urban green areas in central Europe. The behavioral responses of male moths to hexane extracts of whole bodies of calling females or males were tested under laboratory conditions. Only extracts of females elicited responses from males. Analysis of extracts by coupled gas chromatography/electroantennographic detection revealed the presence of two electroantennogram-active peaks. Structure elucidation of these compounds, by gas-chromatography/mass spectrometry and independent synthesis revealed them to be (3Z,6Z,9Z)-tricosa-3,6,9-triene and (3Z,6Z,9Z,19Z)-tricosa-3,6,9,19-tetraene. While the triene was present in both sexes, the tetraene was female-specific. The latter is a new structure for a pheromone component of Lepidoptera and a novel natural product. Field trapping tests, carried out in a mixed oak forest near Budapest (Hungary), using synthetic compounds applied to rubber dispensers, showed that the tetraene per se elicited catches of males in large numbers. When the triene was added to the tetraene in a ratio of 1:1, there was no increase in trap catch; the triene alone did not elicit catches of males. For monitoring this insect, the tetraene, applied to rubber dispensers at a dose of 300 µg, is a potent sex attractant.

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins.

Following our earlier approach to the synthesis of dihydronepetalactones, all eight stereoisomers of trans-fused iridomyrmecins were synthesized starting from the enantiomers of limonene. Combined gas chromatography and mass spectrometry including enantioselective gas chromatography revealed that volatiles released by the endohyperparasitoid wasp Alloxysta victrix contain (4S,4aR,7S,7aR)-iridomyrmecin of 95-97% ee and stereochemically pure (4S,4aS,7R,7aS)-iridomyrmecin as a minor component.

Identification of an insect-produced olfactory cue that primes plant defenses.

It is increasingly clear that plants perceive and respond to olfactory cues. Yet, knowledge about the specificity and sensitivity of such perception remains limited. We previously documented priming of anti-herbivore defenses in tall goldenrod plants (Solidago altissima) by volatile emissions from a specialist herbivore, the goldenrod gall fly (Eurosta solidaginis). Here, we explore the specific chemical cues mediating this interaction. We report that E,S-conophthorin, the most abundant component of the emission of male flies, elicits a priming response equivalent to that observed for the overall blend. Furthermore, while the strength of priming is dose dependent, plants respond even to very low concentrations of E,S-conophthorin relative to typical fly emissions. Evaluation of other blend components yields results consistent with the hypothesis that priming in this interaction is mediated by a single compound. These findings provide insights into the perceptual capabilities underlying plant defense priming in response to olfactory cues.Plants are able to prime anti-herbivore defenses in response to olfactory cues of insect pests. Here, Helms et al. identify the insect pheromone E,S-conophthorin produced by the goldenrod gall fly as the specific chemical component that elicits this priming response in goldenrod plants.

(1R,2S,6R)-2-Hydroxymethyl-2,6-dimethyl-3-oxabicyclo[4.2.0]octane, a new volatile released by males of the papaya borer Pseudopiazurus obesus (Col.: Curculionidae).

Sex-specific volatiles produced by males of the papaya beetle Pseudopiazurus obesus are (1R,2S)-grandisal (1), (1R,2S)-grandisol (2), and the new (1R,2S,6R)-2-hydroxymethyl-2,6-dimethyl-3-oxabicyclo[4.2.0]octane (3) termed papayanol.

Queen sex pheromone of the slave-making ant, Polyergus breviceps.

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers' colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.