Abstract
There has been much discussion on the environmental risks associated with the introduction of exotic natural enemy species on local natural enemy populations. Three species of exotic phytoseiid mites, Typhlodromus occidentalis, T pyri and Amblyseius fallacis from New Zealand, were released into several apple orchards at the Aomori Apple Experiment Station from 1986 to 1992 for the control of spider mites. In the summer of 2003, we surveyed the species composition of phytoseiid mites in the orchards where they were released. No exotic species were found in apple, cherry and willow trees where they were released, and three species of native phytoseiid mites, T vulgaris, A. womersleyi, and A. finlandicus, were found to be dominant. This result suggests that the introduction of exotic phytoseiid mites has no significant ecological effects on native phytoseiid mite species.
