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The functional and numerical responses of the predatory mite Neoseiulus californicus (McGregor) (Phytoseiidae) females reared on thorn apple pollen (Datura stramonium L.) over 40 generations on different densities (2, 4, 8, 16, 32, 64 and 128) of deutonymphs of Tetranychus urticae Koch (Trombidiformes: Tetranychidae) were determined. The results indicated a type II functional response for N. californicus on T. urticae in generations of G0 (no rearing on pollen as control), G10, G20, G30, and G40. The attack rate (α) for N. californicus females increased as the number of generations increased from G0 (0.079 h^-1) to G20 (0.182 h^-1), then decreased in G30 and G40. The longest and shortest handling time (T_h) was observed in G0 (1.670 h) and G40 (0.890 h), respectively. The highest value of maximum attack rate (T/T_h) was estimated in G40 (26.96 prey/day). The equation of the regression line showed that the relationship between the prey density and the number of eggs laid was significant in G0, G10 and G40, and the number of eggs deposited by N. californicus increased with increasing the density of prey. The relationship between the prey density and ECI (the efficiency of conversion of ingested food) was not significant in tested generations. Our findings show that long-term rearing on thorn apple pollen did not affect the type of functional response and efficiency of N. californicus by confirming this predator is an effective biological control agent against T. urticae.