Document Type

Thesis - University Access Only

Award Date

2004

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Jack L. Butler

Abstract

Flea beetles (Aphthona spp.) are often used as biological control agents to reduce the cover and density of leafy spurge (Euphorbia esu/a L.) throughout the northern Great Plains. However, there is concern that the beetles may use alternative hosts for feeding and development. At-risk non-target, native species include those that are most closely related, ecologically and taxonomically, to leafy spurge. A native spurge [Euphorbia robusta (Engem.) Small] is in the same subgenus as leafy spurge and is sympatric with it over much of the northern United States. The objective of this study was to evaluate the actual and potential ecological overlap among leafy spurge, flea beetles, and Euphorbia robusta. The physical and biological characteristics of eight sites, four in SD and four in WY, were evaluated during the 2002 field season. To assess the direct impact of beetles on natural populations of Euphorbia robusta, approximately 3000 black flea beetles (Aphthona /acertosa) were released at each of two sites in SD. Soil cores (10 X 20 cm), containing randomly selected Euphorbia robusta plants, were collected in April 2003, transferred to a greenhouse, and evaluated for beetle emergence. In addition, soil cores with plants were collected and evaluated from a WY site that was immediately adjacent to a population of leafy spurge that had been controlled by flea beetles. Analysis indicates that Euphorbia robusta occurs infrequently and in low densities throughout the region on sites with a high percentage of bare ground in several vegetation types. No beetles emerged from the Euphorbia robusta plants or soil cores and no plant mortality or evidence of use by the beetles either as adults or larvae were detected. Based on evidence collected in this study, the native spurge, Euphorbia robusta, does not appear to be threatened by the flea beetles released as biological control agents to control leafy spurge.

Library of Congress Subject Headings

Leafy spurge -- Biological control.
Flea beetles.
Euphorbia.

Publisher

South Dakota State University

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Rights Statement

In Copyright