Abstract
Changes in the population densities of the peach silver mite, Aculus fockeui, with applications of a synthetic pyrethroid fluvalinate in peach orchards were examined. The injury level of leaves at harvest caused by A . fockeui was significantly higher in trees with an application of fiuvalinate in early July than in those with no applications. Fluvalinate had no effect on A . fockeui, but was extremely harmful to the phytoseiid mite, Amblyseius eharai, which was frequently observed in untreated trees. Population densities of two species of phytoseiid mites, A. sojaensis and A . eharai, were high from June to August in a peach orchard with no applications of fluvalinate, whereas phytoseiid mites did not occur until early September in a peach orchard where fluvalinate had been sprayed 6 times from late April to early July. This resulted in the peak density of A. fockeui reaching ca. 3 times the size of that in the former orchard. These results indicate that a marked resurgence of A. fockeui would occur because of the exclusion of phytoseiid mites when synthetic pyrethroids, which have no effect on A . fockeui and are harmful to the predators, are sprayed.
