Empirical studies in Ecology have shown that insect herbivores feeding on plants with high concentrations of secondary metabolites are more likely to be successfully parasitized. This dissertation research examined one potential mechanism by which plant secondary metabolites render herbivores vulnerable to attack by natural enemies: secondary metabolites may have a negative effect on the physiology and immune response of lepidopteran larvae (caterpillars). An experimental approach tested the novel hypothesis that herbivores feeding on plants with high concentrations of iridoid glycosides and amides/imides are more likely to be successfully parasitized because of a weakened immune response In controlled experiments when the specialist nymphalid caterpillar, Junonia coenia, sequestered high levels of iridoid glycosides it was immunocompromised compared to caterpillars sequestering at low concentrations. The immune response of the generalist arctiid caterpillar, Grammia incorrupta, was not affected by feeding on diets with high concentrations of iridoid glycosides. The effects of imides/amides on caterpillar immune responses were also tested using specialist geometrid caterpillars, Eois spp., and the generalist noctuid caterpillar, Spodoptera exigua. There was no significant effect of the imides/amides on the immune response of any of these caterpillars. Lastly, the immune response was measured across 15 species of caterpillars from 10 different families. Caterpillars with a strong immune response were less likely to be parasitized. When compared to other defenses against parasitoids, the defensive value of the immune response against parasitoids is at least an order of magnitude greater than behavioral or morphological defenses Together, these results show that both plant chemistry and natural enemies play an influential part in determining diet breadth of caterpillars. Many ecological studies have shown that caterpillars that specialize on specific host plants and evolve to sequester the host plant secondary metabolites are protected from predators due to their acquired toxicity. However, the data from this dissertation research show that this is not always the case, and that caterpillars sequestering in high concentrations are immunocompromised and may be susceptible to greater parasitism. The current paradigm of how plant-caterpillar-predator interactions are structured should take into account more specialized interactions like those shown in this dissertation / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_26693 |
| Date | January 2008 |
| Contributors | Smilanich, Angela M (Author), Dyer, Lee (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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