The purpose of this study was to examine the impact of birch pollen (Betula pendula Roth.) on the efficacy of the predatory mite Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) as a biological control agent for the two spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) at different predator release ratios. The experiments were conducted on apple cv. Golden Delicious at 1:5, 1:15 and 1:30 predator-prey release ratios in a climate room (25 +/- 2 degrees C, 65 +/- 10% RH and 16:8 L:D). The predatory mites were also offered pollen grains daily (0.5-0.10 mg/leaf) on the apple seedling during the experiments. One week after the release of K. aberrans, significant reductions in T. urticae density were observed at a ratio of 1:5; and the density remained at low levels thereafter, especially in the pollen experiments. The highest mean numbers of T. urticae in the control group (no predator release) were observed in week 3 with 4067 mites per leaf and 4922 mites per leaf, respectively for the pollen and no pollen application plots. This study demonstrates the potential of K. aberrans to effectively control T. urticae at ratios of 1:5 and 1:15 within three weeks, especially at a ratio of 1:5 when the pollen was added. Furthermore, releasing K. aberrans at the appropriate time and ratio enabled more successful control of T. urticae populations and plant damage, and subsequently kept the mites at low levels.