Semester of Graduation

Spring 2024


Master of Science (MS)



Document Type



Phragmites australis, a wetland grass that stabilizes the Louisiana coastline, has been undergoing a major die-off near the Mississippi River Delta (MRD) since the autumn of 2016. One suspected cause for this plant decline is the attack of an invasive scale insect, Nipponaclerda biwakoensis. We lack information on the host preference of the crawlers, the life stage that decides where to settle and when to start feeding on the plant. The objectives of this study were to identify what positions along the vertical stem N. biwakoensis prefers to settle and what host-plant traits may be influencing this choice. We recorded the within-plant vertical distribution patterns of N. biwakoensis in a natural setting, as well as an artificial setting using a behavioral experiment. We also investigated physical and chemical traits in relation to N. biwakoensis settling choice. We quantified physical (stem toughness and water content) and chemical (carbon, nitrogen, C:N ratio, phenolics, and volatiles) traits of P. australis along the vertical stem in infested and non-infested plants, as well as in both Delta and European lineages of P. australis. We predicted that infested plants would have lower stem toughness and water content as well as emit an increased number of diverse volatiles in response to herbivory. We expected that crawlers would settle higher on the stem, where new growth with higher concentrations of nitrogen is typically found. We found, however, that N. biwakoensis preferred the bottom portion of the stem in natural field settings and seldom chose to settle at the top in both natural and artificial counts. The bottom portion of the stem was found to have a higher C:N ratio and contain lower nitrogen and total phenolics. With this data, conservationists will be able to improve restoration efforts and v fill in the knowledge gaps around N. biwakoensis infestation by applying this research to further studies of the MRD landscape.



Committee Chair

Stout, Michael

Available for download on Friday, April 04, 2025