Date of Graduation

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Philosophy (PhD)

Degree Level

Graduate

Department

Entomology

Advisor

Robert N. Wiedenmann

Committee Member

Timothy J. Kring

Second Committee Member

Frederick M. Stephen

Third Committee Member

Neelendra Joshi

Fourth Committee Member

Nilda Roma Burgos

Keywords

Biological Control, Larinus Minutus, Map, Mowing, Roadside, Spotted Knapweed

Abstract

Spotted knapweed, Centaurea stoebe, is an invasive weed found throughout much of the United States. Spotted knapweed is a rangeland weed where it was originally introduced into western North America in the 1880s.Where spotted knapweed spread to the southeastern U.S., it is found mostly along roadsides. It has been the focus of a biological control program beginning in the 1960s, with 12 insects established, with the final introductions occurring in the 1990s. After the success observed in the western U.S. and Canada with one of these insects, Larinus minutus, this weevil was established in northwestern Arkansas. It is too early to assess the reduction of knapweed in Arkansas. Limits on the impact of this agent may result from the frequent disturbance of the plant and L. minutus by mowing. Field studies were conducted to measure the impact of temporal availability of floral resources on ovary maturation, egg production, and larval mortality of L. minutus. Presence of L. minutus, and spotted knapweed seed production, height, and cover were recorded. Reduced availability of floral resources and delay of access to floral resources delayed ovary development and reduced egg production. Increased larval mortality was observed in the areas of the spotted knapweed patch that had been mowed. Mowing resulted in fewer total seeds in the capitula. Both mowed and un-mowed areas had capitula containing mature seeds and seeds damaged by L. minutus feeding. The number of seeds damaged by L. minutus increased as the proportion of capitula with L. minutus increased in the patch. A survey of 2245km of highways in Carroll, Benton, Madison, and Washington counties found knapweed was present along 13.9% of the highway kilometers. Mowing times could be altered to avoid disturbance of L. minutus from late spring-summer when knapweed produces the most blooms. However, preservation of this weed biological control agent would need to become a consideration in future highway weed management decisions.

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