Control efficiency of the predatory mites, N. californicus and P. persimilis, for T. urticae on a spatially-structured strawberry leaf disc arena at different temperatures

Tetranychus urticae is one of major strawberry pests, and Neoseiulus californicus and Phytoseiulus persimilis have been used as biological control agents for control of T. urticae. We investigated interactions between T. urticae and N. californicus and between T. urticae and P. persimilis on a spatially-structured strawberry leaf disc area at different temperatures to compare their control efficiency for T. urticae. The experimental arena was an array of leaf discs (3 cm diameter) placed upside down on a water-saturated cotton pad in an aluminum pan (17.4x21.5 cm). Twenty leaf discs (4x5) were placed adjacent each other for allowing dispersal of T. urticae and its predatory mites. The temperature conditions were 20, 25, and 30°C. The population densities of T. urticae controlled by N. californicus were different at tested temperatures (F_{2, 257}=3.69, P=0.0262) but T. urticae populations were not different in Tu+Pp treatments (F_{2, 238}=1.26, P=0.2847). The control efficiency of P. persimilis for T. urticae was better than that of N. californicus at all temperatures tested. N. californicus and P. persimilis aggregated in higher density patch of T. urticae after introducing in strawberry leaf disc. The aggregation level of N. californicus was different between growth and declined phase of population density but P. persimilis presented similar patterns. The diffusion of predatory mites was fasted with increasing temperature.