Date of Graduation

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology

Advisor/Mentor

Kring, Timothy J.

Committee Member

Wiedenmann, Robert N.

Second Committee Member

Stephen, Frederick M.

Third Committee Member

Gentry, Johnnie L. Jr.

Fourth Committee Member

Tullis, Jason A.

Keywords

Biological sciences; Invasive plant; Larinus minutus; Short-term-perennial plant; Spotted knappweed; Urophora quadrifasciata

Abstract

Spotted knapweed is an invasive, short-term-perennial plant that is native to Eurasia. It was accidentally introduced into North America in the early 1890's and has since spread across The United States and Canada. Spotted knapweed degrades rangelands and pastures by negatively impacting native plants, increasing soil surface runoff and stream sediment yields, and reducing soil infiltration. A biological control program for spotted knapweed using Larinus minutus (Coleoptera: Curculionidae), was initiated in Arkansas in 2008. In this dissertation I described the releases of L. minutus and investigated the adult activity in the southeastern United States (Chapter 1), investigated the effects of timed mowings on spotted knapweed and the effect of these mowings on L. minutus (Chapter 2), investigated the efficacy of L. minutus in reducing spotted knapweed infestations (Chapter 3), determined if there were any interactions between L. minutus and Urophora quadrifasciata (Chapter 4), and determined if it was feasible to use multispectral remote sensing to detect and monitor spotted knapweed populations. Releases of L. minutus were made at 39 sites in 7 different counties between 2008 and 2012. Thorough monitoring of the sites indicated establishment of the weevil. In Arkansas, L. minutus emerges earlier in the year than in the Pacific Northwest, but is still univoltine. It was determined that the most effective time for mowing spotted knapweed when L. minutus is not present is May, but if weevils are present in high numbers the most opportune time is in July. L. minutus reduced spotted knapweed seed production and rosette densities, but monitoring of the release sites needs to continue for several more years to document the impact of the release program on spotted knapweed in the region. The occurrences of Larinus minutus and Urophora quadrifasciata in the capitula of spotted knapweed are not independent of each other, although, this interaction had no effect on the number of seeds found in a capitulum. Finally it was determined that it is feasible to detect spotted knapweed with multispectral remote sensing throughout the growing season and it is feasible to monitor the change in spotted knapweed populations due to control efforts.

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