Interspecific Variation Within the Genus <Emphasis Type="Italic">Asclepias</Emphasis> in Response to Herbivory by a Phloem-feeding Insect Herbivore |
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Authors: | Caralyn B Zehnder Mark D Hunter |
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Affiliation: | (1) Institute of Ecology, University of Georgia, Athens, GA 30602, USA;(2) Department of Ecology and Evolutionary Biology and School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI 48109, USA |
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Abstract: | Induced plant responses to leaf-chewing insects have been well studied, but considerably less is known about the effects of
phloem-feedings insects on induction. In a set of laboratory experiments, we examined density-dependent induction by the milkweed-oleander
aphid, Aphis nerii, of putative defenses in four milkweed species (Asclepias incarnata, Asclepias syriaca, Asclepias tuberosa, and Asclepias viridis). We hypothesized that high aphid density would lead to increased cardenolide expression in species with low constitutive
levels of cardenolides (e.g., A. tuberosa), but that there would be no induction in high constitutive cardenolide species (e.g., A. viridis). Based on previous studies, we did not expect cardenolide induction in A. incarnata. Contrary to our predictions, we observed feeding-induced declines of cardenolide concentrations in A. viridis. Cardenolide concentrations did not respond to aphid feeding in the other three milkweed species. Aphids also caused reductions
in biomass accumulation by two of four Asclepias species, A. viridis and A. incarnata. High aphid density led to a decrease in A. viridis foliar nitrogen concentration. However, aphids had no effect on the defensive chemistry, growth, or nutritional quality of
either A. syriaca or A. tuberosa. Our results highlight that congeneric plant species may respond differently to the same levels of herbivore damage. |
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Keywords: | Aphis nerii Asclepias Cardenolide Density-dependence Induction milkweeds Plant defense |
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