Life history traits of Tetranychus urticae Koch on three legumes (Acari: Tetranychidae)Abstract : The two-spotted spider mite, Tetranychus urticae Koch, is very polyphagous and considered a serious pest world-wide. The divers host plant species may have been the different effects of this pest; we therefore compared population growth parameters of T. urticae reared on three commonly grown and important legumes in Iran (soybean, cowpea and bean). The life table parameters were estimated at 25 ± 1oC, 60 ± 10% RH, and a photoperiod of 18:6 h (L: D). Egg hatchability, development time and survival to adult stage were similar among cultivars, but we detected significant variation in fecundity and longevity, resulting in large differences for population growth parameters such as the intrinsic rate of natural increase (rm), net reproductive rate (R0), finite rate of increase (ë) and doubling time (DT). Soybean was the most favorable host for two-spotted spider mites with rm = 0.296 (offsprings/female/day), followed by cowpea (0.242) and bean (0.230). The slowest population growth was observed on the bean species with rm = 0.214. These findings indicate that the choice of host plant species will affect how fast spider mite populations reach damaging levels in a culture.