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  • 1990-1994  (2)
  • 1880-1889
  • 1993  (2)
  • Phorodon humuli  (1)
  • aeration  (1)
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  • 1990-1994  (2)
  • 1880-1889
Year
  • 1
    ISSN: 1573-1561
    Keywords: Damson-hop aphid ; Phorodon humuli ; Homoptera ; Aphididae ; methyl salicylate ; (E)-2-hexenal ; β-caryophyllene ; semiochemicals ; aggregation ; attractant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Behavioral studies using an olfactometer demonstrated that spring migrants of the damson-hop aphid,Phorodon humuli, respond to semiochemicals released by spring migrants feeding on hop leaves. Samples of the total volatiles released on feeding were analyzed by coupled gas chromatographysingle cell recording techniques and showed the presence of several active components. Three compounds were identified, using coupled gas chromatography-mass spectrometry, as methyl salicylate, (E)-2-hexenal andβ-caryophyllene. These three compounds elicited responses from separate olfactory receptors on the antenna. In the olfactometer, both (E)-2-hexenal andβ-caryophyllene gave positive responses from spring migrants, and a mixture of the two compounds in the natural ratio was more attractive than (E)-2-hexenal alone. Addition of methyl salicylate eliminated the response to the active binary mixture.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9680
    Keywords: root growth ; soil compaction ; aeration ; soil strength ; soil moisture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Tree growth and soil physical properties were compared on two grazed plots planted with sycamore at 5 and 10 m square spacing on an upland Scottish site. Both plots received fertilizer and stocking density of ewes and lambs was adjusted to maintain a constant sward height. Mean tree height in 1990 and height increment (1988–90) were significantly greater in the 5 m spaced plot (P〈0.05). Although matric potential under the trees was generally greater than in the grassed rows between trees, mean penetration resistance (37–107 mm depth) was significantly greater (P〈0.01) under the trees. Even when the soil was close to field capacity, less than 10% of penetrometer readings were 〈 1 MPa under the trees, in comparison to 44% in grassed areas between trees. This demonstrates that surface compaction due to preferential treading by sheep near the base of trees was sufficient to have seriously reduced tree root growth. Penetration resistance under the 5 m spaced trees was significantly less (P〈0.05) than under the 10 m spaced trees. A technique for estimating the probability of root deflections by stones (in 35 mm depth intervals), Ps, from penetrometer readings was used. A significant relationship (P〈0.1) was found between tree height increment and depth to Ps≥0.4 in the 10 m plot.
    Type of Medium: Electronic Resource
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