Biological control of apple spider mites by Metaseiulus occidentalis Nesbitt (Acari: Phytoseiidae).

Botetranychus pruni (Oudeman) and Tetranychus viennensis Zacher, two major species of red spider mites in arid and semi-arid apple growing regions of northwestern China, were used as prey for the predatory mite, M. occidentalis, in laboratory rearings. The predator developed normally and was released in apple orchards of Lanzhou, Gansu from late May to early June, 1983-85. The releases were made at a predator : pest ratio of 1 : 36-64, with 350-2,750 female adult predators per tree. Exact quantity for the release was determined according to the age of trees and pest mite infestation levels. Effective control of the two pest mites was achieved 45-60 days after the releases. Decline of the pest mite numbers occurred gradually following a period of slow development of their populations. Complete suppression of the pest mites led to a reduction of 3-4 applications of miticides in the releasing year, and a prolonged effect for the following year.