Entomology, Department of


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A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Entomology, Under the Supervision of Professors J.D. Bradshaw & G.L. Hein. Lincoln, Nebraska: December, 2014

Copyright (c) 2014 Rudolph J. Pretorius


This study investigated the effect of several agricultural practices on the sugar beet root aphid (Pemphigus betae Doane) and beneficial epigeal natural enemies in western Nebraska sugar beet agroecosystems. Eight glyphosate-tolerant sugar beet varieties were evaluated under field conditions for their resistance to root aphids. High levels of aphid resistance were detected for some varieties. In conjunction to this, pitfall sampling was conducted to determine the beneficial epigeal natural enemy complex in the area, which could contribute to the management of both root aphids and glyphosate-resistant weeds. Ground beetles comprised an important and abundant component of this fauna, with 79 species collected throughout this study.

The second investigated the impact of a seed-applied insecticide (Poncho Beta) and sugar beet plant density (25,000 plants/acre vs. 35,000 plants/acre) on root aphids and beneficial epigeal arthropods. The insecticide significantly reduced root aphid populations, but not to levels which can be considered adequate control. Soil-dwelling beneficial arthropods remained largely unaffected by the seed-applied insecticides, except for a single ground beetle species (Bembidion quadrimaculatum oppositum) which showed higher activity in the untreated plots during one of the years. Plant density had minimal impact on the aphids and beneficial arthropods.

Finally, this study also investigated the impact of tillage (conventional versus reduced tillage) on beneficial epigeal arthropods, and their associated ecosystem services (particularly weed seed consumption and predation of live prey). Overall, the results indicated a strong incentive for adopting reduced tillage practices for sugar beet production, based on increased activity of spiders, centipedes and rove beetles. Although prey consumption remained unaffected by the tillage system used, increased weed seed consumption was observed under the zone tillage system. This study also illustrated the importance of examining important beneficial taxa, such as ground beetles, on the species level rather than on the family level, based on their differing responses to tillage by different species.

Advisers: Jeffrey D. Bradshaw and Gary L. Hein