2-SPOTTED SPIDER-MITE (ACARI, TETRANYCHIDAE) AND PHYTOSEIULUS-PERSIMILIS (ACARI, PHYTOSEIIDAE) ON GREENHOUSE ROSES - SPATIAL-DISTRIBUTION AND PREDATOR EFFICACY

Interaction between twospotted spider mite, Tetranychus urticae Koch, and the predatory mite, Phytoseiulus persimilis Athias-Henriot, on ros es was studied in a greenhouse at Cornell University. In the absence o f predators, the spider mite population showed typical S-shaped growth and averaged approximate to 4-fold increases in density in 3 wk. In t he presence of predators, spider mites showed an initially slow (<50%) increase followed by a decline concurrent with a rapid increase of pr edators. Spider mites were nearly eliminated within 5 nk of the introd uction of the predators. Most spider mites were found on the lower can opy when their overall density was low but more mites were found on th e upper canopy when their density increased, especially in the absence of predators. Both spider mites and predators were strongly aggregate d. The dispersion of spider mites was similar in the upper and lower c anopy and was not affected by the presence of predators. Regressions o f predator density on prey density revealed 44% positive density-depen dent aggregation. The strength of aggregation increased with predator density and was positively associated with the suppression of prey pop ulation. The spider mite population growth rate was negatively related to both predator and spider mite density; the effect of predator dens ity on the growth rate was 35 times greater than that of spider mite d ensity. Potential for control of T. urticae on roses through pest popu lation monitoring and the integration of chemical and biological contr ol is discussed.