Background: The tomato russet mite, Aculops lycopersici, is a major worldwide pest infesting tomato crops for which only few control methods are available. At present, no commercialized beneficial organism has proven to be an effective biological control agent of the pest. As there is a strong need to develop alternatives to synthetic insecticides, we assessed the efficacy of an iolinid mite, Pronematus ubiquitus, as a preventive method against A. lycopersici in comparison with a curative treatment in a replicated experiment in the greenhouse. Results: After pre-establishment of P. ubiquitus supplied with cattail pollen, followed by infestation of A. lycopersici, the predator was able to reduce pest populations by 98% as compared with control plants. Probably due to lack of food and high temperature, the number of P. ubiquitus decreased during the season and so the Eriophyid population rose, along with crop damage. The sulphur treatment could stop the progress of A. lycopersici, but their population levels remained high. Conclusion: Pronematus ubiquitus has great potential to prevent the establishment of the tomato russet mite. Even if a curative treatment affects the pest mite, the use of a preventivemethod is preferable as such insecticides/acaricides are harmful for beneficials and are applied after symptom appearance, when the pest pressure is already high. Despite the need to optimisemanagement of the predator throughout the season, P. ubiquitus proved to be able to establish successfully on tomato plants.