The European hazelnut, Corylus avellana L., was imported into the U.S. in the late 1800's and is now grown throughout the Willamette Valley in Oregon. A native species of hazelnut, C. cornuta Marshall, is a common shrub found in forested areas of the Pacific Northwest. Foliage of both C. avellana and C. cornuta was sampled using beating sheets. The objectives of the study were as follows: 1. To compile a complete list of the Coleoptera and Heteroptera fauna of both species of hazelnut. 2. To determine the amount of overlap across host plants. 3. To measure arthropod abundance and species diversity within functional groups across a forest-edge-orchard gradient. 4. To use ordination techniques to determine where peak abundance of individual taxa occur along the forest-edge-orchard gradient. One hundred and thirty-two species of Coleoptera and forty-nine species of Heteroptera were identified on Hazelnut foliage. The most abundant Heteroptera in the orchards studied is a newly introduced mirid predator, Malacocoris chlorizans (Panzer). There is a great deal of overlap between the two hazelnut species. Most differences are attributed to rare species. Diversity and abundance of predaceous Coleoptera and Heteroptera were severely hindered by IPM management practices, involving insecticide usage, within the orchards. However, the organic orchards retained high levels of diversity and abundance of predaceous Coleoptera and Heteroptera in the centers of the orchards. The organic orchards had higher diversity of phytophagous Coleoptera and Heteroptera as compared to IPM orchards, but the abundance of those insects was not different between the IPM and organic orchards. The ordinations of the Coloeptera data show that the peak abundances of individual species often shift along the forest-edge-orchard gradient over time and that the organic orchards retain peak abundances of predaceous Coleoptera even in late season. The ordinations of the Heteroptera data show that several mirid predators are at their peak abundances within the orchards of both IPM and organic orchards. / Graduation date: 2000