Air-entrained Samples Research Articles

Male-Produced Sex Pheromone of Tibraca limbativentris Revisited: Absolute Configurations of Zingiberenol Stereoisomers and their Influence on Chemotaxis Behavior of Conspecific Females.

The rice stalk stink bug, Tibraca limbativentris, is an important rice pest in Brazil with a high invasive potential for Mexico and the USA. The sex pheromone of this species was previously identified as a combination of two stereoisomers of 1,10-bisaboladien-3-ol (zingiberenol), but the absolute configurations of these sesquiterpenes were not determined, neither were their effect(s) on T. limbativentris behavior evaluated. In this study, using two chiral columns, we compared retention times of the two natural 1,10-bisaboladien-3-ol stereoisomers from air-entrainment samples of male T. limbativentris with those of synthetic stereoisomers of 1,10-bisaboladien-3-ol. The results showed that T. limbativentris males produce (3S,6S,7R)-1,10-bisaboladien-3-ol (1) and (3R,6S,7R)-1,10-bisaboladien-3-ol (5) as their sex pheromone. Two new minor, male-specific components were also identified as cis and trans isomers of 2,10-bisaboladien-1-ol (sesquipiperitol). Y-tube olfactometer bioassays showed that the major (3S,6S,7R) isomer 1 was essential for attraction of T. limbativentris females, but the minor (3R,6S,7R) isomer 2 was not, nor did it show synergistic/antagonistic effects when added to the major isomer. The (1S,6S,7R) and (1R,6S,7R) stereoisomers of sesquipepiritol also attracted T. limbativentris females.

Effect of sulphate corrosion on the durability of air-entrained cement mortars

Sulphate corrosion is a complex sequence of chemical and physical processes that, when the aqueous sulphate solutions are exposed for a sufficiently long time, irreversibly destroys the microstructure of cement paste. In order to determine the durability of Portland cement mortars, mortar resistance tests were carried out on a 5% solution of sodium sulphate by measuring linear deformations. The tests included 1 series of non air-entrained mortars and 3 series of air-entrained mortars with air content: 7%, 10% and 13%. The biggest deformations were observed for non air-entrained samples, the smallest for mortar with an air content of 13%. Compressive strength tests of mortars after 28 days and 80 weeks of residence in a solution of sodium sulphate were also carried out. For all mortars, the strength measured after 80 weeks immersion in Na2SO4 increased in relation to the strength after 28 days of maturation. Observations of the cement mortar microstructure using a scanning electron microscope (SEM-EDS) showed that ettringite was present in both the C-S-H structure and the air pores. By means of XRD analysis, the occurrence of crystalline materials was detected. Based on the research, it was found that air-entrained cement mortars showed greater durability in the context of sulphate corrosion.

Mechanical properties and durability of roller compacted concrete pavements in cold regions

Roller compacted concrete pavement is a cost effective and beneficial pavement system which needs fewer material and less energy than other kinds of pavements. An important problem with the pavements is salt scaling that occurs due to a saline solution on cementitious surfaces. In order to reduce the negative effects of salt scaling, the influence of cement replacement by trass, a natural pozzolan, has been investigated. Mechanical and durability tests and salt scaling with air void analysis on hardened concrete were carried out to evaluate the effect of ordinary/trass selected mixes with/without air entraining agents. Results generally showed that although usage of air entraining agents reduced compressive and tensile strengths and increased water permeability and capillary absorption, it performed well against salt scaling in freeze-thaw cycles. The control samples with less w/c performed better than trass samples. In this research, spacing factor obtained about 0.07mm and 0.1mm for air-entrained and non air-entrained samples respectively.

Identification of Host Kairomones from Maize, Zea mays, for the Maize Weevil, Sitophilus zeamais

The maize weevil, Sitophilus zeamais, is an economically important pest of stored grains in tropical and subtropical regions of the world. The behavioral responses of adult S. zeamais to volatile organic compounds (VOCs) from maize seeds, Zea mays, were studied to identify semiochemicals used in host location and provide potential tools for managing this pest. VOCs released directly from crude seed extracts, vacuum distilled extracts, hexane and diethyl ether fractions from silica gel chromatography of the vacuum distillates, air entrainment samples, and identified volatile compounds were assayed using a Perspex four-arm olfactometer. Weevils spent significantly more time, and made a higher number of visits, to the region of the olfactometer where Z. mays volatiles were present than in control regions comprising solvent only. When white and yellow Z. mays VOCs were compared in a choice test, the mean time spent in the two olfactometer treatment arms was significantly greater than the mean time spent in the control arms. However, weevils did not show any preference for either of the two treatments, thus demonstrating that both varieties of maize have similar activity. Gas chromatography (GC), coupled gas chromatography-mass spectrometry (GC-MS), GC peak enhancement and electroantennography (EAG) identified hexanal, (E)-2-heptenal, and octanal as biologically active compounds in air entrainment samples and diethyl ether fractions of vacuum distillates. A 3-component synthetic blend of the identified compounds was significantly attractive to both sexes of the weevil. These host kairomones could be deployed in semiochemical based monitoring and management of S. zeamais in the tropics.

Effect of glass fiber-reinforced polymer and epoxy injection on compressive strength of elevated temperature damaged concrete

SUMMARY Glass fiber-reinforced polymer (GFRP) materials have received a great deal of interest among civil engineers during the past decade. This paper presents an overview of experimental studies carried out on GFRP-wrapped and epoxy-injected concrete samples exposed to elevated temperatures. For this purpose, 0.30, 0.35 and 0.40 water to binder (w/b) ratios were used. For each w/b ratio, normal aggregates were replaced by lightweight aggregates with a size fraction of 0–2 mm at three different volume fractions such as 10%, 20% and 30% of total aggregate volume. At the same time, a group of air-entrained samples was also cast for each w/b ratios. Prepared samples were exposed to 600 °C for 3 h. The damaged samples were separately repaired by GFRP and epoxy injection. Before and after elevated temperature exposure, water absorption and compressive strength were tested. After repairing with GFRP and epoxy injection, only the compressive strength test was carried out. GFRP improved the compressive strength between 1–22% and 348–1403% for samples before and after being exposed to elevated temperatures, respectively. Epoxy injection increased the compressive strength of the samples, exposed to elevated temperature, between 1% and 123%. However, the epoxy injection process failed to recover the compressive strength of the samples before elevated temperature exposure. Copyright © 2012 John Wiley & Sons, Ltd.

Agriotes proximus and A. lineatus (Coleoptera: Elateridae): a comparative study on the pheromone composition and cytochrome c oxidase subunit I gene sequence

The presence of geranyl octanoate, previously found in pheromone gland extracts of Agriotes lineatus females, was also demonstrated in gland extracts of A. proximus females. Similar to A. lineatus, geranyl butanoate was present only in trace amounts in A. proximus female gland extracts. In air entrainment samples of female A. lineatus and A. proximus beetles, the relative ratio of geranyl butanoate and geranyl octanoate was higher than that in gland extracts. In addition, comparison of a segment of the mitochondrial cytochrome c oxidase subunit I gene of feral specimens of A. lineatus and A. proximus showed >99% similarity. Both pheromone profile and nucleotide sequence analysis delineate close relationship between the investigated taxa and postulate taxonomic revision. Further studies on sympatric populations of A. lineatus and A. proximus are underway to investigate and better understand possible processes of species diversification.

Behavioural and chemical ecology underlying the success of turnip rape (Brassica rapa) trap crops in protecting oilseed rape (Brassica napus) from the pollen beetle (Meligethes aeneus)

There is increasing interest in the use of trap crops as components of integrated pest management (IPM) strategies. Understanding the mechanisms underlying host plant preferences of herbivorous pests can lead to improved effectiveness and reliability of the trap crop. We investigated the behavioural and chemical ecology underlying the success of turnip rape, Brassica rapa, trap crops in protecting oilseed rape, Brassica napus, from the pollen beetle, Meligethes aeneus, which feeds in the flowers and lays its eggs in the buds causing yield loss. Using a semi-field arena bioassay, plant growth stage was found to be a major factor in the preference of this pest for B. rapa over B. napus. Plants at early-flowering growth stages were preferred over plants in the bud stage, irrespective of species. No preference was found when both species were flowering. As B. rapa develops faster than B. napus in the field, this could explain part of the mechanism of its success as a trap crop. However, B. rapa was preferred over B. napus when both species were in the bud stage, indicating some inherent preferences for B. rapa. Responses of M. aeneus in olfactometer tests to the odours of B. napus and B. rapa at the bud and flowering growth stages, reflected those of the semi-field arena bioassay. These behavioural responses can be explained by volatile compounds associated with the flowering stage. Phenylacetaldehyde, indole and (E,E)-α-farnesene were found to be present in air entrainment samples of both plant species at the flowering growth stage, but only in those of B. rapa at the bud stage. The former two compounds were behaviourally-active in olfactometer tests. These compounds are likely to be involved in host location by M. aeneus, and, at least partially, responsible for the attractiveness of B. rapa and its success as a trap crop to protect B. napus from this pest.

Responses of Female Orange Wheat Blossom Midge, Sitodiplosis mosellana, to Wheat Panicle Volatiles

Air entrainment samples of volatiles from panicles of intact wheat, Triticum aestivum, cultivar 'Lynx' were collected at the ear emergence/early anthesis growth stage. In an olfactometer bioassay, both freshly cut panicles and an air entrainment sample were found to attract female orange wheat blossom midge adults, Sitodiplosis mosellana. Coupled gas chromatography-electroantennography (GC-EAG) analyses of panicle volatiles located six electrophysiologically active components. These were identified by coupled gas chromatography-mass spectrometry and coinjection with authentic standards, on polar and nonpolar GC columns, as acetophenone, (Z)-3-hexenyl acetate, 3-carene, 2-tridecanone, 2-ethyl-1-hexanol, and 1-octen-3-ol. Although none of these was active when presented individually at the levels present in the entrainment sample, acetophenone, (Z)-3-hexenyl acetate, and 3-carene were active in the olfactometer when presented at a higher dose of 100 ng on filter paper. However, the six-component blend and a blend of acetophenone, (Z)-3-hexenyl acetate, and 3-carene, in the same ratio and concentration as in a natural sample, was as attractive to female S. mosellana as the whole air entrainment sample.

Identification of Floral Volatiles Involved in Recognition of Oilseed Rape Flowers, Brassica napus by Honeybees, Apis mellifera

Volatiles from oilseed rape, Brassica napus, flowers were sampled by air entrainment and their relevance to the natural odor profile of the flowers was confirmed by conditioned proboscis extension (CPE) assays with honeybee, Apis mellifera L., foragers. Coupled gas chromatography (GC)-CPE analysis of the air entrainment samples was used to locate key compounds involved in the recognition of B. napus flowers, and the compounds were then identified using coupled gas chromatography-mass spectrometry and comparison with authentic samples. Six regions of the gas chromatograms elicited CPE responses from bees previously conditioned to the total extract, and from these areas 16 compounds were identified that elicited CPE activity from conditioned bees when tested with synthetic samples. Eight of the 16, α-pinene, phenylacetaldehyde, p-cymene, α-terpinene, linalool, 2-phenyl-ethanol, (E,E)-α-farnesene, and 3-carene, gave the highest responses. When the bees were conditioned to the total extract of flower volatiles, a mixture of the eight components elicited responses from 83% of the individuals, suggesting that the eight-component mixture accounted for a major part of the CPE activity of the total extract. In addition, a mixture of the three most active compounds, phenylacetaldehyde, linalool, and (E,E,)-α-farnesene, evoked responses from 85% of the bees after the latter had been conditioned to the eight-component mixture. Thus, these three compounds appear to play a key role in the recognition of the eight component mixture and, by inference, of oilseed rape flowers.

Effect of primary‐host kairomones on the attractiveness of the hop‐aphid sex pheromone to Phorodon humuli males and gynoparae

The damson-hop aphid, Phorodon humuli (Schrank), is a pest of world-wide importance for hop growers. It is an obligate holocyclic aphid with various Prunus species serving as the primary host and Humulus lupulus L., the hop, as its sole secondary host (Eppler, 1986). P. humuli develops winged forms in late spring and autumn, coinciding with the beginning and end of the hop’s vegetative period respectively. Recent work suggests that aphids utilise kairomonal and pheromonal olfactory cues in their environment to locate host plants and mates, respectively (Hardie et al., 1990; Nottingham et al., 1991). For P. humuli Campbell et al. (1993) described volatile components of the hop ‘headspace’ involved in location of the secondary host. Earlier, Campbell et al. (1990) identified cis, cis-nepetalactol as the probable sex pheromone from the analysis of air-entrainment samples of volatiles released by the sexual females.