Pergamasus quisquiliarum Canestini is a polyphagous predatory mite that has been shown to feed on the economically important arthropod, Scutigerella immaculata Newport (Symphyla: Scutigerellidae), Collembola, Diptera larvae, Enchytraeid worms, and miscellaneous other soil organisms. This study examined the feeding behavior of P. quisquiliarum, the effects of cover cropping and tillage practices on P. quisquiliarum populations, the biology and ecology of P. quisquiliarum in agricultural and non-agricultural sites, and the seasonal dynamics of P. quisquiliarum. The interaction of cover crop and tillage treatment was statistically significant for P. quisquiliarum populations (P<0.001). Tillage treatment was the primary factor for P. quisquiliarum populations, as very low densities of P. quisquiliarum were recovered from green manure plots, regardless of the cover crop treatment. Among no-till plots, Monida oats had the greatest densities of P. quisquiliarum, while control (fallow) and white mustard plots had the lowest densities. The two non-agricultural sites had higher densities of P. quisquiliarum than the agricultural site. Among the non-agricultural sites, P. quisquiliarum density was higher in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) litter than in Oregon white oak litter (Quercus garryana Dougl.), suggesting that the nature of the chemical and physical micro-environment was more suitable under Douglas-fir trees. In all sites, P. quisquiliarum attained it's greatest density in August, with a second peak in October. Minimum P. quisquiliarum densities were observed in January and February. Seasonal P. quisquiliarum densities were significantly synchronized with seasonal dynamics of it's prey items. / Graduation date: 1998