Semiochemicals from bark beetles: New results,remarks, and reflections

A brief survey is given about recent results in the identification of semiochemicals in bark beetles: Males ofIps sexdentatus (Boern.), stressed by the attack on resinous trees produce large amounts of 3(S)-1-methyl-5-(1-hydroxyl-1-methylethyl)-cyclohexa-1,3-diene. The compound appears to be derived from ³-carene and acts as a repellent. Males ofIps typographus (L.), stressed through the attack on unsuitable host material release 3-methyl-7-methylene-1,3(E), 8-nonatriene, which seems to act as a repellent. The odor bouquet of three species ofPityogenes is described. The occurrence of (+)-grandisol and other compounds related to weevil pheromones points to a close relation between Scolytidae and Curculionidae. Females ofDendroctonus simplex (Le Conte) use (–)-frontalin as the main pheromone. 6-Methyl-6-hepten-2-one, a minor component among the volatile compounds released by the females, is regarded as a possible precursor of frontalin. Similarly, (2R,5S)-2(1-hydroxyl-1-methylethyl)-5-methyltetrahydrofuran, pityol, a pheromone ofPityophthorus spp., is regarded to at least share a common biogenetic precursor with 6-methyl-5-hepten-2-ol, sulcatol. A new bicylic acetal, 2-ethyl-1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane, is described as an aggregation pheromone of the beech bark beetle,Taphrorychus bicolor (Herbst). Structural relationships between bark beetle pheromones and plant volatiles are 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.     

A chiral sex pheromone system in the pea midge, Contarinia pisi

The sex pheromone of the pea midge consists of 2-acetoxytridecane, (2S,11S)-diacetoxytridecane and (2S,12S)-diacetoxytridecane. The responses of male pea midges to the corresponding stereoisomers of (2S,11S)-diacetoxytridecane and (2S,12S)-diacetoxytridecane were tested in field trapping experiments and by electroantennographic recordings. When added at 20% of the pheromone component to the sex pheromone blend, the (2S,11R)- and (2R,11S)-stereoisomers of (2S,11S)-diacetoxytridecane, were shown to have a strong inhibitory effect on male attraction in the field. At the same dose, (2R,11R)-diacetoxytridecane, (2R,12R)-diacetoxytridecane, and meso-2,12-diacetoxytridecane, did not have a significant effect on male behavior. It was also shown that substitution of either (2S,11S)-diacetoxytridecane or (2S,12S)-diacetoxytridecane with the related stereoisomers reduced trap catches to the level of blank traps. The electroantennographic recordings showed similar dose–response curves for the pheromone components and the stereoisomers shown to have an inhibitory effect. It seems likely that male antennae have receptors for both pheromone components and for inhibitory stereoisomers. Scanning electron microscopy and transmission electron microscopy of the antennae revealed three types of sensilla involved in chemoreception: sensilla circumfila, sensilla trichodea, and sensilla coeloconica. The sensilla circumfila and trichodea are both innervated by two sensory cells, whereas the sensilla coeloconica are innervated by four to five cells.     

Chemistry of fruit flies: Nature of glandular secretion and volatile emission ofBactrocera (bactrocera) cacuminatus (Héring)

The major component of the rectal glandular extract and volatile emission of maleBactrocera cacuminatus is racemic 1,7-dioxaspiro[5.5]undecane. l-Hydroxy-5-nonanone as its open chain form, together with 6-n-butyl-3,4-dihydro-2H-pyran are minor components. 1,7-Dioxaspiro[5.5]undecan-4-ol is present at a low level and is shown to be exclusively the diastereomer with an equatorial hydroxy group by comparison with synthesized samples of both epimers. Examination of the trifiuoroacetate by chiral gas chromatography has established the (4S,6S) stereochemistry (ca. 80% ee). The presence of 1,7-dioxaspiro[5.5]undecan-3-ol, or its isomerization product, 1,6-dioxaspiro[4.5]decan-2-ylmethanol, could not be confirmed. Trapping of the volatiles released by sexually mature male flies at dusk revealed that a number of the glandular components described above are released at mating time. Reexamination of the glandular secretion of sexually mature female olive flies (B. oleae) has failed to confirm the presence of any 1,7-dioxaspiro[5.5]undecanols, with the only volatile component (other than fatty acids) being 1,7-dioxaspiro[5.5]undecane.     

Identification of a novel moth sex pheromone inEriocrania cicatricella (Zett.) (Lepidoptera: Eriocraniidae) and its phylogenetic implications

Extracts from different body parts of adult femaleEriocrania cicatricella (Zett.) were tested for electrophysiological activity on conspecific male antennae. Extracts from the Vth abdominal segment, containing a pair of exocrine glands, elicited the largest electroantennographic response when compared to extracts of other body parts. Female extracts were analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). The EAD active peaks were identified as (Z)-4-hepten-2-one, (2R)-heptane-2-ol, and (2R)-(Z)-4-hepten-2-ol by coinjection on a gas chromatography and by comparison of mass spectra with those of synthetic standards. In field tests, a blend of these three pheromone components was highly attractive to conspecific males, and a subtractive assay confirmed that the unsaturated alcohol is the major pheromone component, whereas no definite behavioral activity could be assigned to the ketone or the saturated alcohol. A bait containing the two alcohols withS-configuration was attractive to maleE. sparrmannella (Bosc), whereas no males ofE. cicatricella were found in these traps. The sex pheromone compounds inE. cicatricella are chemically similar to pheromones reported in Trichoptera and they are produced in homologous glands.     

Identification of a Novel Moth Sex Pheromone Component from <Emphasis Type="Italic">Chilecomadia valdiviana</Emphasis>

Chilecomadia valdiviana (Philippi) (Lepidoptera: Cossidae) is an insect native to Chile. The larval stages feed on the wood of economically important fruit tree species such as apple, pear, olive, cherry, and avocado, and also on eucalyptus. This causes weakening and, in case of severe infestation, death of the tree. We report identification of the sex pheromone produced by females of this species. Hexane extracts of the abdominal glands of virgin females were analyzed by gas chromatography (GC) with electroantennographic detection, GC coupled with mass spectrometry, and GC coupled to infrared spectroscopy. The major pheromone component was identified as (7Z,10Z)-7,10-hexadecadienal (Z7,Z10–16:Ald), and minor components present in the extracts were (Z)-7-hexadecenal and (Z)-9-hexadecenal, hexadecanal, and (9Z,12Z)-9,12-octadecadienal. Structural assignments were carried out by comparison of analytical data of the natural products and their dimethyl disulfide adducts with those of authentic reference samples. In field tests, traps baited with Z7,Z10–16:Ald captured significantly more males than control traps.     

The Chemical Ecology of Cecidomyiid Midges (Diptera: Cecidomyiidae)

The family of cecidomyiid midges (Diptera: Cecidomyiidae) exhibits diversified patterns of life history, behavior, host range, population dynamics and other ecological traits. Those that feed on plants include many important agricultural pests; most cultivated plants are attacked by at least one midge species. Several features of the reproductive biology of cecidomyiid midges point to an important role for chemical communication, with this topic last reviewed comprehensively 12 years ago. Here, we review progress on identification of sex pheromones, chemicals involved in location of host plants, the neurophysiology of reception of volatile chemicals, and application of semiochemicals to management of pest species of cecidomyiid midges that has occurred during the last decade. We hope this review will stimulate and sustain further research in these fields.     

Workers Make the Queens in <Emphasis Type="Italic">Melipona</Emphasis> Bees: Identification of Geraniol as a Caste Determining Compound from Labial Glands of Nurse Bees

Reproductive division of labor in advanced eusocial honey bees and stingless bees is based on the ability of totipotent female larvae to develop into either workers or queens. In nearly all species, caste is determined by larval nutrition. However, the mechanism that triggers queen development in Melipona bees is still unresolved. Several hypotheses have been proposed, ranging from the proximate (a genetic determination of caste development) to the ultimate (a model in which larvae have complete control over their own caste fate). Here, we showed that the addition of geraniol, the main compound in labial gland secretions of nurse workers, to the larval food significantly increases the number of larvae that develop into queens. Interestingly, the proportion of queens in treated brood exactly matched the value (25%) predicted by the two-locus, two-allele model of genetic queen determination, in which only females that are heterozygous at both loci are capable of developing into queens. We conclude that labial gland secretions, added to the food of some cells by nurse bees, trigger queen development, provided that the larvae are genetically predisposed towards this developmental pathway. In Melipona beecheii, geraniol acts as a primer pheromone representing the first caste determination substance identified to date.     

Variation of Floral Scent Emission and Postpollination Changes in Individual Flowers of Ophrys sphegodes Subsp. sphegodes

We investigated the scent composition of individual flowers of Ophrys sphegodes, its alteration following pollination, and of picked flowers by day and at night. Odor samples were collected by headspace sorption and analyzed by gas chromatography and mass spectrometry. To evaluate the function of postpollination odor changes, we carried out behavioral tests on the pollinator Andrena nigroaenea with pollinated and unpollinated flowers. We identified 27 volatiles in the flower scents. Aldehydes and alkanes were most frequently found. Aldehydes were the most abundant class of compounds (40–50%). When flowers were picked, they emitted significantly lower total amounts of volatiles than unpicked flowers, and their odor bouquets were significantly different. Comparison of scents released by day and at night showed no decrease in scent emission during nighttime, but the odor bouquets were significantly different. Pollinated flowers produced significantly different odor bouquets, and the total amount of scent emitted two to four days after pollination was significantly lower compared with unpollinated flowers. In addition, behavioral tests with A. nigroaenea males showed that flowers were significantly less attractive three days after pollination. This reduced attractiveness is hypothesized to guide pollinators to the unpollinated flowers within an inflorescence, and thus increase the reproductive success of the plant.     

Hydride-Meisenheimer complex formation and protonation as key reactions of 2,4,6-trinitrophenol biodegradation by Rhodococcus erythropolis

Biodegradation of 2,4,6-trinitrophenol (picric acid) by Rhodococcus erythropolis HLPM-1 proceeds via initial hydrogenation of the aromatic ring system. Here we present evidence for the formation of a hydride-Meisenheimer complex (anionic sigma-complex) of picric acid and its protonated form under physiological conditions. These complexes are key intermediates of denitration and productive microbial degradation of picric acid. For comparative spectroscopic identification of the hydride complex, it was necessary to synthesize this complex for the first time. Spectroscopic data revealed the initial addition of a hydride ion at position 3 of picric acid. This hydride complex readily picks up a proton at position 2, thus forming a reactive species for the elimination of nitrite. Cell extracts of R. erythropolis HLPM-1 transform the chemically synthesized hydride complex into 2,4-dinitrophenol. Picric acid is used as the sole carbon, nitrogen, and energy source by R. erythropolis HLPM-1.