Document Type

Thesis - Open Access

Award Date

2024

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Lora Perkins

Abstract

North American monarch butterfly (Danaus plexippus) populations are experiencing significant declines due to habitat loss caused by land use changes. Much of the American Midwest where milkweed, the only host plant of the monarch butterfly, was once much more abundant has been converted to a predominantly agricultural landscape. There are nineteen species of milkweed native to the northern Great Plains region occupied by South Dakota, North Dakota, and Minnesota. Some of these milkweed species may be preferable to monarch butterflies for different reasons, including morphological factors such as stem length, species-level chemical factors, and temporal factors. As monarch butterfly populations continue to decline, more information on milkweeds native to the northern Great Plains is needed to streamline efforts for monarch butterfly habitat restoration. The two objectives of this study were to 1) analyze monarch butterfly oviposition preferences on native milkweeds of the northern Great Plains and 2) conduct a survey of different pathogenic fungi isolated from native milkweed species in the northern Great Plains. To address the first objective, a common garden plot of the species of milkweed native to the Northern Great Plains was established near South Dakota State University. Using randomized block design, multiple plants of each milkweed species were planted in replicate plots, and each plant was thoroughly checked for eggs and larvae and measured for morphological factors, including stem length, width, and number of stems. Asclepias incarnata received the highest number of eggs and larvae throughout all three years of study, but monarchs laid more eggs on A. syriaca at the beginning of each season, suggesting changes in preference throughout the summer. Morphological factors were found to play no role in monarch oviposition preferences. The second objective was to survey the different species of fungus isolated from tissue samples collected from a variety of different milkweed species located in the common garden plot. Disease symptoms and high death rates were noted on various milkweed species, particularly Asclepias tuberosa, in the common garden plot throughout the 2023 season. DNA from the fungi collected from milkweed tissue samples was sequenced to determine which fungal species were the most likely culprits of the disease symptoms noted on milkweed in the common garden plot. We suspect Rhizoctonia solani to be the source of plant deaths early in the season and Fusarium acuminatum to be the source of shoot tip dieback symptoms later in the season.

Publisher

South Dakota State University

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Rights Statement

In Copyright