Date of Award
Shannon M. Murphy, Ph.D.
Host choice, Lepidoptera, Polyphagy, Trade-offs
Host use in herbivores is determined by a variety of ecological drivers, including bottom-up and top-down selective pressures such as host abundance, host plant quality, and parasitism pressure. If the relative importance and strength of interactions among these selective conditions change over an herbivore’s geographic range, local patterns of host use should change in response, evident in differing diet breadths. The fall webworm (Hyphantria cunea) is a widespread, polyphagous moth with two color morphs, red and black-headed. In the eastern United States, fall webworms feed on dozens of plant species and previous research demonstrated that host plant abundance was the only significant predictor of host plant use. Populations of fall webworm in Colorado are found on considerably fewer host plant species than populations farther east. We investigated the impacts of host abundance, larval performance, and parasitism on patterns of host use for fall webworm in Colorado to determine whether differences in selective pressures may explain why these populations are relatively more specialized compared to previously-studied populations. Additionally, we used DNA sequences from fall webworms collected across their geographic range to investigate genetic variation via phylogenetic tree building and AMOVAs. Using those genetic techniques, we found that red-headed and black-headed fall webworms are not reproductively isolated, but there are two genetic groups: one that is exclusively black-headed and one that is both red and black-headed. Similar to studies on eastern populations, we found that host abundance was a significant predictor of host use. We also found a trade-off between host quality, as measured by larval performance, and percent parasitism. Host plants that supported larvae with higher fitness, as measured by survival, pupal weight, feeding efficiency, and development time, also had a greater proportion of larval mortality due to parasitism. Local patterns of host plant abundance may lead fall webworms to a relatively restricted diet in Colorado compared to the east coast, while the trade-off between quality and parasitism may explain the maintenance of a generalized feeding strategy.
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Loewy, Katrina J., "Host Use and Geographic Variation in Fall Webworms (Hyphantria cunea)" (2013). Electronic Theses and Dissertations. 379.
Received from ProQuest
Katrina J. Loewy