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Production of Glands in Leaves of Porophyllum Spp. (Asteraceae): Ecological and Genetic Determinants, and Implications for Insect Herbivores

Gabriel Guillet, Francois Lorenzetti, Andre Belanger, John T. Arnason and Elizabeth A. Bernays
Journal of Ecology
Vol. 85, No. 5 (Oct., 1997), pp. 647-655
DOI: 10.2307/2960535
Stable URL: http://www.jstor.org/stable/2960535
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Production of Glands in Leaves of Porophyllum Spp. (Asteraceae): Ecological and Genetic Determinants, and Implications for Insect Herbivores
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Abstract

1 The mean number of translucent glands containing potent insecticidal allelochemicals in leaves of Porophyllum gracile was observed to vary up to nearly twofold under field conditions in the area of Tucson, Arizona (USA). 2 The production of glands appeared to be a beneficial trait to reduce herbivory in the field since individuals of P. gracile bearing 2.5 glands per leaf were submitted to an approximately fivefold higher herbivory pressure than those having 4.8 glands per leaf. 3 To investigate if the production of glands in leaves of P. gracile is under genetic control, seeds were collected from individuals for which this trait varied under field conditions. There was no correlation for the mean number of glands per leaf between individuals of P. gracile sampled in the field and their progeny seedlings grown under controlled conditions. This suggested that the production of glands in leaves of P. gracile is not strongly hereditary. 4 The resource allocated to the formation of foliar glands, which was determined as the ratio of total volume of glands per unit area of leaf, in seedlings of P. ruderale and P. gracile was enhanced by up to one order of magnitude by both nitrogen fertilization, 15 vs. 0 mM of NO- 3 in the watering solution, and high light regime, 380 vs. 50 μmole photon m-2 s-1. These results suggest that the production of glands in leaves of Porophyllum spp. depends greatly on resource availability. 5 The natural plasticity in the production of glands in leaves of P. ruderale was in turn employed in controlled laboratory experiments to confirm the potential benefit of the glands to repress insect herbivory as observed in the field. It was demonstrated that adults of the red-legged grasshopper are repelled by the volatiles emitted from the glands and that they feed less on leaves bearing more glands.

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