Pyrethroid Lambdacyhalothrin-Induced Population Increase of Tetranychus urticae Koch (Acari:

J. Agric. Entomol. l(}(3):197-203 (July 1993) ABSTRACT Based on data from apple trees without the presence of any predatory mites, the effect of the pyrethroid lambdacyhalothrin on population density of the twospotted spider mite, Tetranychus urticae Koch, is reported. Results show that significantly (P < 0.05) higher numbers of T. urticae were found in pyrethroid·treatcd trees relative to the untreated controls, indicating that lambdacyhalothrin has a stimulatory effect on the mite population. Pyrethroid application had a significant (P < 0.05) effect on the spatial distribution of motile mites. All IW8o's 13 values for the mite in the untreated control trees were significantly greater (P < 0.05) than those in the pyrethroid·treatcd trees, indicating that T. urticae were less aggregated in the field following pyrethroid applications. Pyrethroid-induced population increase of T. urticae in the field may result from alteration of its spatial distribution.