Document Type

Thesis - University Access Only

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Kelley J. Tilmon

Abstract

The soybean aphid, Aphis glycines Matsumura, was introduced to the United States in 2000, and has become the dominant and most damaging insect pest in soybean in the North Central region. The bean leaf beetle (Cerotoma trifurcata Forster) is also an important pest in soybean in this region. Integrated pest management seeks to maximize control of such pests and minimize environmental impacts by coordinating multiple tactics, including use of resistant varieties, tactical deployment of insecticides, and promotion of natural enemies. This study examines the interaction of these factors by documenting insect pest and natural enemy population responses in four studies: ( 1) a field study on aphid-resistant soybeans ( containing the Rag 1 gene) with and without insecticidal seed treatment, (2) a field study on three breeding lines containing singlegene aphid resistance or pyramided resistance (Rag] and/or Rag2 genes), (3) a greenhouse study quantifying aphid population growth on these types of soybeans, and ( 4) a field study examining natural enemy recruitment in different soybean environments (aphid-resistant and seed-treated). All of the resistant lines in these studies significantly reduced soybean aphids compared to controls. Peak aphid densities were maintained below the economic injury level, and below or just above the economic threshold. Inclusion of Rag], thiamethoxam seed treatment, or both significantly reduced cumulative aphid days and significantly increased yield in the host plant resistant and Vl seed treatment study. Highest yield was obtained from seed-treated Rag] soybeans. Thiamethoxam seed treatment also reduced bean leaf beetles. In a non-choice test in the greenhouse, there was complete mortality of aphids on thiamethoxam-treated soybeans, strong aphid resistance on Rag2 and Rag 11 Rag2 pyramided soybeans, and similar aphid densities between Rag] soybeans and susceptible controls (suggesting the greenhouse colony may have developed virulence to Ragl). All resistant soybean lines tested, and thiamethoxam-treated soybeans had lower natural enemy populations than the controls. Harmonia axyridis Pallas and Orius insidiosus Say, were the dominant predators, and the family Aphelinidae was dominant among aphid parasitoids in the study. In the natural enemy recruitment experiment (where aphid densities were artificially manipulated), plants which had initially high aphid density had greater natural enemy abundance than plants that were initially aphid-free. Aphids declined on high-density plants by more than four-fold compared to plants of moderate aphid density over a five-day period, suggesting density-dependence of natural enemies to soybean aphids. This result suggests that natural enemies have great potential to regulate soybean aphid populations.

Library of Congress Subject Headings

Soybean -- Disease and pest resistance
Insecticides
Aphids
Bean leaf beetle
Biological pest control agents

Publisher

South Dakota State University

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Rights Statement

In Copyright