Prey suppression by predators depends on effective predator: prey release ratios. The effectiveness of Phytoseiulus persimilis Athias-Henriot and Typhlodromus bagdasarjani Wainstein and Arutunjan was evaluated at different predator: prey release ratios for suppression of Tetranychus urticae Koch populations on cucumber plants in the microcosm condition based on three experiments. In the first experiment, 7 days after T. urticae releases, the most reduction in the different stages (densities) of T. urticae and the most increase in both P. persimilis and T. bagdasarjani were observed in predator: prey release ratio of 1:4 followed by ratios of 1:10 and 1:20. In the second experiment, one day after T. urticae release at predator: prey release ratio of 1:4, there was no significant difference between predators effect on the decline of T. urticae stages (densities). In this case, more T. bagdasarjani at all stages was observed on the plants in comparison with P. persimilis. According to the third experiment, 7 days after T. urticae release, there was no significant difference between predator: prey ratio of 1:4 of P. persimilis and 1:2 of T. bagdasarjani on T. urticae suppression. In this case, more P. persimilis was observed on plants in comparison with T. bagdasarjani. Our study demonstrates that the most suppression of T. urticae populations occurred in predator: prey ratio of 1:4 for both predators. Based on our findings, we suggest that P. persimilis and T. bagdasarjani can be released at a ratio of 1:4 for successful control of T. urticae on cucumber.

Keywords: Biological control, Predatory mites, Spider mites.

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