Abstract: The two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae) is a seriouspest in Austrian greenhouse vegetable production, against which the predatory mitePhytoseiulus persimilis (Acari: Phytoseiidae) usually provides effective and rapid control.However, heat waves are predicted to occur more frequently in summer, affecting the efficacyof the heat sensitive P. persimilis in greenhouses. To ensure sustainable spider mite control inthe future we hypothesized that the Japanese predatory mite species Neoseiulus womersleyi(Acari: Phytoseiidae) could be a heat-tolerant alternative to P. persimilis. Hence, at dailytemperature fluctuations with maximum temperatures (Tmax) of 38 °C, 35 °C and 32 °Csimulating heat waves, we analyzed the spider mite predation and the fecundity of the predatorymites regarding egg number and size on three consecutive days. According to our laboratoryexperiments, both species displayed thermal plasticity by higher predation rates and smalleregg sizes under heat stress. Egg production of N. womersleyi, but not P. persimilis, peaked atTmax of 38 °C. Additionally, the survival probability of N. womersleyi individuals was higher,irrespective of temperature. To sum up, increased predation but lower reproduction and smalleregg size, as well as decreased survival indicated increased heat stress for P. persimilis incontrast to N. womersleyi. Therefore, we assume that the Japanese species would be a suitablebiological control agent in Austrian greenhouses. Nevertheless, N. womersleyi is an alienspecies, therefore its establishment risk has to be evaluated before it can be introduced as aspider mite predator.