Tarbiat Modares University Journal of Agricultural Science and Technology 1680-7073 20 3 2018 05 01 Effect of Different Predator: Prey Release Ratios of Phytoseiulus persimilis and Typhlodromus bagdasarjani (Acari: Phytoseiidae) on Reduction of Tetranychus urticae (Acari: Tetranychidae) on Cucumber under Microcosm Conditions تأثیر نسبت‌های مختلف رهاسازی شکار: شکارگر در دو کنه شکارگر Phytoseiulus persimilis و Typhlodromus bagdasarjani بر کاهش جمعیت کنه تارتن Tetranychus urticae روی خیار در شرایط میکروکازم 509 518 16161 EN M. Moghadasi Department of Plant Protection, College of Agriculture and Natural Resources, University of Tehran, Karaj, Islamic Republic of Iran. H. Allahyari Department of Plant Protection, College of Agriculture and Natural Resources, University of Tehran, Karaj, Islamic Republic of Iran. Journal Article Prey suppression by predators depends on effective predator: prey release ratios. The effectiveness of <em>Phytoseiulus persimilis</em> Athias-Henriot and <em>Typhlodromus bagdasarjani</em> Wainstein and Arutunjan was evaluated at different predator: prey release ratios for suppression of <em>Tetranychus urticae</em> Koch populations on cucumber plants in the microcosm condition based on three experiments. In the first experiment, 7 days after <em>T. urticae</em> releases, the most reduction in the different stages (densities) of <em>T. urticae</em> and the most increase in both <em>P. persimilis</em> and <em>T. bagdasarjani</em> 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 <em>T. urticae</em> release at predator: prey release ratio of 1:4, there was no significant difference between predators effect on the decline of <em>T. urticae</em> stages (densities). In this case, more <em>T. bagdasarjani</em> at all stages was observed on the plants in comparison with <em>P. persimilis</em>. According to the third experiment, 7 days after <em>T. urticae</em> release, there was no significant difference between predator: prey ratio of 1:4 of <em>P. persimilis</em> and 1:2 of <em>T. bagdasarjani</em> on <em>T. urticae </em>suppression. In this case, more<em> P. persimilis</em> was observed on plants in comparison with <em>T. bagdasarjani</em>. Our study demonstrates that the most suppression of <em>T. urticae</em> populations occurred in predator: prey ratio of 1:4 for both predators. Based on our findings, we suggest that <em>P. persimilis</em> and <em>T. bagdasarjani</em> can be released at a ratio of 1:4 for successful control of <em>T. urticae</em> on cucumber. https://jast.modares.ac.ir/article_16161_85dc7996f092d5ad5a652fac6079bd57.pdf