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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Biology and Microbiology

First Advisor

Jonathan Lundgren


Multitrophic interactions are often overlooked by scientists in favor of smaller and simpler systems. With these simple systems key pieces of crucial information are often missing, resulting in a large gap in knowledge of how to utilize these multitrophic systems in agricultural systems in ways that are beneficial. The objectives of these studies were to better understand multitrophic interactions that occur on the oilseed crop canola in South Dakota, and whether these interactions cause negative or positive effects on the local abundance and species richness of other predators and herbivores within the same shared system. In this study a series of interactions in canola (Brassica napus) were mimicked using Formica montana ants, green peach aphids (Myzus persicae), pink spotted lady beetles (Coleomegilla maculata), along with imported cabbageworm (Pieris rapae). Initially, ant-tended aphids were tested to determine if aphids act as mediators between ants and P. rapae eggs, and if ants will protect eggs from predation by lady beetles. Ants and lady beetles were found to consume all eggs regardless of the presence xiii of aphids, suggesting that ants can be an important source of pest management for other herbivores, but other predators can impact these interactions. Maternal preference was tested with the presence aphids and lady beetle larva separately and in combination. Results showed that butterflies were not deterred by aphids alone on plants, but in combination with predacious lady beetle larvae there were significant differences in the number of eggs laid. These results indicate that competing herbivores had little to no effect on oviposition behavior while the combination of a competing herbivore and predator will cause the females to lay their eggs elsewhere. When taken into the field setting it was found that as the number of aphids increased, so did the number of ants. As both the number of ants and aphids decreased as the growing season progressed due to changes in climate and plant physiology, the number of predators also decreased, allowing P. rapae pest the opportunity to exploit competitor free resources. These results indicate that a population of aphids can contribute to pest management within a field.

Library of Congress Subject Headings

Multitrophic interactions (Ecology)
Pieris rapae
Green peach aphid
Spotted lady beetle


Includes bibliographical references (pages 66-74)



Number of Pages



South Dakota State University


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