Technical Abstract: The twospotted spider mite, Tetranychus urticae (Acari: Tetranychidae), is an important pest of vegetables and other crops. This study was conducted to evaluate and compare the potential role of three commercially available predators, predatory gall midge, Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae), new predacious mite species, Amblyseius swirskii, and Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), as biological control agents of T. urticae. The functional responses at prey densities and prey-stage preferences (when offered T. urticae eggs and nymphs) of these predators were investigated under laboratory conditions. F. acarisuga was highly effective and the two species of predacious mites were modestly effective in regulating T. urticae egg densities. Logistic regression analysis suggested a Type II (convex) functional response for all three species: the numbers of prey consumed increased with prey density up to a maximum point after which it slowly began to decrease. The maximum daily predation was recorded (50 eggs / female / day) by larva F. acarisuga at a prey density of over 100 T. urticae eggs per arena, followed by female N. californicus (26 eggs /day) and female A. swirskii ( 15 eggs /day) at a density of 70-79 eggs per arena. Our results on prey-stage preferences showed that all three predator species exhibited no-prey stage preference to prey eggs or nymphs. Among the three species, F. acarisuga had the highest predation potential, in particular at high prey densities. These results are discussed in relation to feeding behavior and the habits of the phytoseiids and their potential for biological control of T. urticae in greenhouse vegetable production.