Suppressive Effect of Euseius sojaensis or Amblyseius eharai（Acari: Phytoseiidae）on Tetranychus kanzawai（Acari: Tetranychidae）on Japanese Pear

Abstract

Five phytoseiid mite species: Phytoseiulus persimilis Athias-Henriot, Neoseiulus californicus（McGregor）, Neoseiulus womersleyi（Schicha）, Amblyseius eharai Amitai and Swirski, and Euseius sojaensis（Ehara）（Acari: Phytoseiidae）were collected from commercial Japanese pear orchards in Shizuoka Prefecture. To evaluate the suppressive effect of generalist phytoseiid species on the spider mite Tetranychus kanzawai Kishida（Acari: Tetranychidae）, we compared four treatments（E. sojaensis release, A. eharai release, synthetic pyrethroid application, and no-release）performed in a greenhouse. These treatments were conducted when T. kanzawai densities were low, and pine pollen was provided as alternative food for predatory mites in all treatments. At late June, the peak densities of T. kanzawai were significantly low in E. sojaensis release and in no-release compared with in pyrethroid application and in A. eharai release. The dominant phytoseiid species in E. sojaensis release and in no release was E. sojaensis. After July, however, E. sojaensis densities became lower in E. sojaensis release as well as no-release, and thus T. kanzawai densities became higher in all treatments at early August. These results suggest that conservation and augmentative release of E. sojaensis prior to T. kanzawai population increase, might suppress the outbreak of this spider mite in Japanese pear orchards until early summer.