Semester of Graduation

summer 2020

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

Common reed, Phragmites australis, is the dominant plant in the Mississippi River Delta (MRD), Louisiana. Phragmites australis stands reduce soil erosion from wave action, protect the oil infrastructure, and freshwater habitats. In the fall of 2016, widespread reed die-backs in the MRD were associated with outbreaks of an invasive scale Nipponaclerda biwakoensis (Hemiptera: Aclerdidae). Due to the recent detection of the scale, there was limited knowledge of its ecology in the adventive range, and its impacts on P. australis lineages. Therefore, the objectives of my thesis were to determine (1) the host specificity of the N. biwakoensis in important economic grasses closely related to P. australis, and (2) to evaluate the chemical defenses traits of P. australis lineages against N. biwakoensis.

The host specificity of N. biwakoensis was determined by conducting a no-choice experiment that demonstrated that nymphs established not only on P. australis, but also on Spartina alterniflora, and Schoenoplectus californicus. However, the survival to adult experiment revealed that N. biwakoensis only stablished on P. australis. Moreover, spill-over surveys at the MRD showed the presence of N. biwakoensis just on P. australis. Therefore, N. biwakoensis appears to be a specialist insect on P. australis and is unlikely to threaten other grasses with agronomic or environmental value in Louisiana.

The reed lineages Delta, European, Greeny, and Gulf are present in Louisiana. However, the Delta genotype is dominant in the MRD. Previous studies suggested that the European lineages are more resistant to herbivores. Research was needed to determine the defensive chemistry of the different reed lineages and their role in host-plant resistance. Therefore, we evaluated the survival of N. biwakoensis, quantified phenolics by the Folin-Ciocalteau method from leaf tissue; and silica by the Molybdenum Blue calorimetric procedure. European lineages had less scale insects than Delta. In addition, the European lineages had 1.28- and 1.39-times more phenolics and silicon, respectively, than the Delta. Therefore, European lineages may have resistance traits against N. biwakoensis. This information will be critical when selecting common reed lineages during the implementation of restoration projects in the MRD.

Committee Chair

PhD

Available for download on Thursday, June 29, 2023

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