Document Type

Thesis - University Access Only

Award Date

2003

Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Billy W. Fuller

Abstract

Corn rootworms, Diabrotica spp. (Chrysomelidae: Coleoptera), are serious economic insect pests in maize producing regions of the United States. Larvae feed on root tissue causing root pruning that often leads to plant lodging, and potentially severe yield reductions. Traditional management of the corn rootworm often involves the utilization of insecticides. A maize hybrid containing a Cry3Bb1 protein derived from Bacillus thuringiensis kumamotoensis, displays activity against several species of Diabrotica larvae. Due to the amount of insecticides farmers use for corn rootworm control, this hybrid may have great potential in reducing the amount of insecticides used. Reducing insecticide use may help to conserve beneficial arthropods. The minute pirate bug, Orius tristicolor White, and green lacewings, Chrysoperla spp., are among the most common generalist predators found in Midwestern maize fields. Additionally, these beneficials are omnivorous and draw on the maize plant for its pollen as a high protein food source. Therefore, this feeding behavior on plant material from Cry3Bb1 hybrids could potentially threaten these beneficials. To determine if this new rootworm-resistant hybrid posed any problems, research was conducted near Brookings, South Dakota during 2001 and 2002. Population estimates of these two beneficial insects in transgenic, insecticide treated (tefluthrin), and non-treated rootworm management fields were gathered using Pherocon® AM sticky traps and whole-plant counts for a ten week time period. Plots were approximately 1.6 ha., and samples were taken only in the central hectare to reduce potential problems often associated with small plot size. Pherocon® AM sticky trap season totals for Chrysoperla adults in 2001 and 2002 did not have any significant (X2 = 2.60; df = 2; P = 0.2728 and X2 = 1.85; df = 2; P = 0.3975) differences among the three treatments. Whole-plant sampling of the larval, and adult stages of Chrysoperla displayed similar results, however, season totals of Chrysoperla eggs found significant (X2 = 57 .29; df = 2; P < 0.0001) differences among treatments with more eggs recorded within Cry3Bb1 maize. Unlike Chrysoperla, O. tristicolor numbers found on Pherocon® AM sticky traps over the entire season in 2001 were found to be significant (X2 = 108.90; df = 2; P < 0.0001 ). Specifically, sticky traps from Cry3Bb1 and untreated plots contained significantly (X2 = 101.35; df = 1; P < 0.0001 and X2 = 10.42; df = 1; P = 0.0012) more 0. tristicolor overall. No significant ( P > 0.05) differences were found among treatments from the 2002 season totals of 0. tristicolor gathered from Pherocon® AM sticky traps. Whole-plant sampling of 0. tristicolor adults in 2002 displayed similar results to Pherocon® AM trap sampling in 2001. Significant (X2 = 1 2.61 ; df = 2; P = 0.0018) differences existed between treatments when comparing the O. tristicolor whole-plant season totals, with more abundant numbers collected from samples of the transgenic maize fields than the untreated or tefluthrin treatments. Overall, no negative effects associated with the Cry3Bb1 hybrid were observed on Chrysoperla and 0. tristicolor in 2001 and 2002. Furthermore, some conservation of beneficials may have occurred in Cry3Bb1 fields since on several occasions there were greater numbers of these insects than that observed in fields treated with insecticides.

Library of Congress Subject Headings

Corn -- Disease and pest resistance -- South Dakota.
Hybrid corn.
Northern corn rootworm -- Control.
Western corn rootworm -- Control.
Chrysoperla. 650 0Orius.

Publisher

South Dakota State University

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Rights Statement

In Copyright