2005 年 2005 巻 52 号 p. 107-109
Exotic phytoseiid mite, Typhlodromus occidentalis from New Zealand, was released into apple orchards at the Nagano Fruit Tree Experiment Station in 1990 and 1991 for the control of spider mites. We surveyed species composition of phytoseiid mites in the orchards after 13 years of its release to evaluate the ecological effects on native phytoseiid mites. No T. occidentalis was found at all and the result was the same as that obtained in Akita and Aomori Prefectures in 2002-2003. We speculate that the introduced T. occidentalis had scarcely any significant ecological effects on native phytoseiid mite species except for only a short time just after its release. Neoseiulus californicus appeared to be highly dominant in these orchards. Furthermore, as there are recently native and alien strains of N. californicus in Japan, it is important to investigate intra- and inter-specific relationships with other native phytoseiid mites.