Theses and Dissertations

ORCID

https://orcid.org/0000-0001-9523-5459

Advisor

Ervin, Gary N.

Committee Member

Turnage, Gray

Committee Member

Folk, Ryan A.

Committee Member

Ward, Samuel F.

Date of Degree

5-16-2025

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

Alligatorweed (Alternanthera philoxeroides), native to South America, is a highly invasive aquatic macrophyte that is globally distributed and particularly problematic in the southeastern United States. In the United States, alligatorweed management has a long history, particularly of chemical and biological control. Alligatorweed management saw early success with a South American flea beetle (Agasicles hygrophila), but this agent’s utility has waned. Despite the long history of alligatorweed invasion, several important research questions remain, and the research in this dissertation seeks to answer some of these questions. This research focuses on multiple and diverse aspects of alligatorweed biology, ecology, and management: (1) the unusual development of seeds in invasive alligatorweed populations, (2) the role and utility of a South American thrips (Amynothrips andersoni) in alligatorweed biological control and integrated vegetation management (IVM), and (3) biotic and abiotic factors that predict the probability of alligatorweed invasion. Multiple instances of seed production were observed in alligatorweed growing under terrestrial, vs. aquatic conditions, but seeds seemed non-viable. Terrestrial conditions were proposed as a stimulus for seed production and polyploidy or low genetic diversity as potential mechanisms for putative non-viability. Ecological niche models of alligatorweed, the thrips, and the flea beetle confirm a poor climate match between the flea beetle and alligatorweed. These model predictions also suggest that the thrips is expected to continue to have a much greater niche overlap with alligatorweed under short-term climate change in the United States. Thrips biological control was tested alongside several submersed herbicide treatments for reducing alligatorweed biomass. While the thrips exhibited significant control, several herbicide chemistries exhibited better control. With the chemistries and rates tested in this research, no chemical controls significantly benefitted from the integration of thrips. Invasion ecology models of alligatorweed show that greater aquatic plant diversity and smaller lake perimeter best predict the presence of alligatorweed invasion in Mississippi lakes. The significant predictors of alligatorweed are contrasted with three other common invasive aquatic plants in the Southeast. Findings from this research will help direct future alligatorweed research and inform resource managers of alternative tools for alligatorweed IVM.

Sponsorship (Optional)

Gulf States Marine Fisheries Commission

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