Patterns of insect occurrence on exotic and native trees

Patterns of insect occurrence on trees and shrubs growing in an exotic habitat are unknown for most species. Robinia neomexicana A. Gray is a common native shrub/tree in northern Arizona. A closely related species native to the eastern United States, R. pseudoacacia L., grows in similar climatic conditions as R. neomexicana. A literature review of the genus Robinia was conducted. This genus was to used determine arthropod species occurrence for a native and a similar non-native species. Arthropods were collected on native locust, Robinia neomexicana A. Gray, and exotic Robinia pseudoacacia L. in northern Arizona over a 2-year period to determine if differences in the number of arthropod species and number of individuals are present. More arthropod species were found on the native (251) than on the exotic Robinia (174). Greater species diversity was likewise found on the native than the exotic. The five most numerous insects collected each year accounted for 81% to 91% of the total number collected on the exotic and native Robinia in 1997 and 1998. Only 12 species occurred on both the native and exotic Robinia each of the two years.; A final study was conducted on the diversity of arthropod species on woody plants in their native habitat compared with the diversity when that same host species was grown as an exotic and when that same genera is growing as a native. Thirty-one pairs of arthropod species data sets were analyzed to determine arthropod diversity on plants grown as exotics. Length of time since introduction of the exotic, and total area of native range and exotic planting was also included in the analysis. The 31 pairs of arthropod data sets were broken into nine additional groups that were used in the analysis. More arthropod species were found to colonize plants growing as a native than the same species grown as an exotic. The most significant differences were seen on the pooled data sets.