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  • 1
    Electronic Resource
    Electronic Resource
    Vertical stratification of feeding by Japanese beetles within linden tree canopies: selective foraging or height per se? (1996)
    Springer
    Oecologia 108 (1996), S. 459-466 
    Details
    ISSN: 1432-1939
    Keywords: Herbivory ; Popillia japonica N. ; Nutritional ecology ; Variability ; Tilia cordata L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Adult Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), tend to aggregate and feed most heavily in the upper canopy of host plants, defoliating them from the top down. We examined characteristics of linden (Tilia cordata L.) foliage from different canopy zones and tested two hypotheses that might account for vertical stratification of feeding by this vagile, polyphagous folivore. In the field, P. japonica caused 4–12 times more damage to upper canopy leaves in full sunlight than to lower canopy leaves in sun or shade. However, this within-tree pattern apparently cannot be explained by differences in nutritional parameters (protein, water, and sugar content) or “defensive” properties (toughness, tannins) of leaves. Furthermore, beetles did not discriminate between foliage from different canopy zones in laboratory choice tests, nor were fecundity or longevity higher for beetles fed upper canopy, sun-exposed leaves. Clonal grape plants suspended from vertical posts in the field at 3.65, 1.83 or 0 m above ground showed a top-down defoliation pattern identical to that seen in linden trees. This suggests that the height of foliage per se strongly affects initial orientation and attack by P. japonica. Recent related studies have shown that both sexes of P. japonica are strongly attracted to host volatiles induced by feeding of conspecific beetles. We suggest that Japanese beetles begin to feed in the upper canopy for reasons unrelated to host nutritional variation (e.g., behavioral thermoregulation, visual orientation to the host silhouette), and that top-down defoliation follows as additional beetles are attracted to feeding-induced volatiles acting as aggregation kairomones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333722
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  • 2
    Electronic Resource
    Electronic Resource
    Inhibition of herbivory on young holly leaves: evidence for the defensive role of saponins (1989)
    Springer
    Oecologia 78 (1989), S. 322-329 
    Details
    ISSN: 1432-1939
    Keywords: Ilex opaca ; Allelochemicals ; Oligonychus ilicis ; Plant defense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Response of the southern red mite, Oligonychus ilicis McGregor, to young and one year old leaves of Ilex opaca Aiton was studied on three dates during the period of leaf expansion in the spring. Young foliage, which is rich in nutrients but also contains high levels of saponins, was found to be unsuitable for colonization by this oligophagous herbivore until the leaves had matured and levels of saponins had declined. Mites preferentially colonized and had higher survival and reproduction on sclerophyllous, one-year old leaves than on young leaves in early spring. High levels of saponins in young, second-flush leaves of shoots that had earlier been damaged by frost were again correlated with low mite survival in June. Laboratory preference tests with the fall webworm, Hyphantria cunea Drury, and the eastern tent caterpillar, Malacosoma americanum (F.), indicated that young, saponin-rich holly foliage is especially unpalatable to these highly polyphagous caterpillars. Fifth instar fall webworms required significantly longer to complete their development, attained lower weights, and had greater mortality on artificial diet amended with low concentrations of purified holly saponins than on control diet. These results support the hypothesis that the high levels of saponins in young holly leaves provide protection from herbovores until the leaves have matured and their structural defenses are developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379105
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  • 3
    Electronic Resource
    Electronic Resource
    Pathogen-activated induced resistance of cucumber: response of arthropod herbivores to systemically protected leaves (1990)
    Springer
    Oecologia 85 (1990), S. 25-31 
    Details
    ISSN: 1432-1939
    Keywords: Cucumis sativus ; Plant defense ; Herbivory ; Insect/microbial interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Restricted (non-systemic) inoculation of cucurbits, green bean, tobacco, and other plants with certain viruses, bacteria, or fungi has been shown to induce persistent, systemic resistance to a wide range of diseases caused by diverse pathogens. The non-specificity of this response has fueled speculation that it may also affect plant suitability for arthropod herbivores, and there is limited evidence, mainly from work with tobacco, which suggests that this may indeed occur. Young cucumber plants were immunized by restricted infection of a lower leaf with tobacco necrosis virus (TNV), and upper leaves were later challenged with anthracnose fungus, Colletotrichum lagenarium, to confirm induction of systemic resistance to a different pathogen. The response of arthropod herbivores was simultaneously measured on non-infected, systemically protected leaves of the same plants. As has been reported before, immunization with TNV gave a high degree of protection from C. lagenarium, reducing the number of lesions and the area of fungal necrosis by 65–93%. However, there was no systemic effect on population growth of twospotted spider mites, Tetranychus urticae Koch, on upper leaves, nor did restricted TNV infection of leaf tissue on one side of the mid-vein systemically affect mite performance on the opposite, virus-free side of the leaf. Similarly, there were no effects on growth rate, pupal weight, or survival when fall armyworm larvae were reared on systemically protected leaves from induced plants. In free-choice tests, greenhouse whiteflies oviposited indiscriminately on induced and control plants. Feeding preference of fall armyworms was variable, but striped cucumber beetles consistently fed more on induced than on control plants. There was no increase in levels of cucurbitacins, however, in systemically-protected foliage of induced plants. These findings indicate that pathogen-activated induced resistance of cucumber is unlikely to provide significant protection from herbivory. The mechanisms and specificity of induced resistance in cucurbits apparently differ in response to induction by pathogens or herbivores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317339
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  • 4
    Electronic Resource
    Electronic Resource
    Early spring defoliation, secondary leaf flush, and leafminer outbreaks on American holly (1989)
    Springer
    Oecologia 81 (1989), S. 192-197 
    Details
    ISSN: 1432-1939
    Keywords: Phytomyza ilicicola ; Ilex opaca ; Herbivory ; Plant defense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Adults of Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, emerge in close synchrony with leaf flush of American holly and feed on and oviposit in soft, partially expanded leaves. Early spring defoliation, such as commonly results from freezing injury to young shoots, is followed several weeks later by a second flush of young leaves from lateral buds. We simulated this phenomenon by manually defoliating whole small trees and individual shoots of large trees to test the hypothesis that freezing injury can encourage leafminer outbreaks by inducing an abundance of soft, protein rich young leaves late in the adult activity period, when availability of vulnerable leaves becomes limited. Defoliation of small trees one or two weeks after bud break resulted in six- to 13-fold increases in the incidence of feeding punctures and larval mines on second flush leaves as compared with densities on original young leaves of control trees. Similarly, we induced significant increases in feeding punctures and larval mines on second flush leaves of individual defoliated shoots, although leaves that did not open until after the flight period escaped this injury. These observations underscore the capability of adult female P. ilicicola to locate and exploit a small number of phenologically available leaves among many hundreds of older leaves on the same tree. By altering the phenology of leaf flush, certain kinds of environmental stress may predispose perennial plants to outbreaks of early season folivores that restrict their feeding or oviposition to very young leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379805
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