Development duration and reproduction rate of the twospotted spider mite Tetranychus urticae Koch (Acarina: Tetranychidae) were studied on five different apple cultivars ('Amasya' (local cultivar), 'Golden Delicious', 'Granny Smith', 'Starking Delicious' and 'Starkrimson Delicious') at 25degreesC, 65 +/- 10% r.h. and 16:8 L:D. In addition, the same parameters were determined on Golden Delicious leaves at three constant temperatures (20degrees, 30degrees and 35degreesC, 65 +/- 10% r.h. and 16:8 LD) in the laboratory. T urticae performed better on Granny Smith than on the other cultivars, due mainly to high daily egg production (4.6 eggs/female/day) and the intrinsic rate of natural increase (r(m), which was 0.243 female/female/day). The lowest r(m) was observed on Amasya variety (0.231 female/female/day). Development periods of immature stages of T urticae varied from 6.5 to 15.5 days at 35degrees and 20degreesC, respectively, for females, and from 5.9 to 14.5 days at 35degrees and 20degreesC, respectively, for males. The development thresholds of the eggs and pre-adult stages, respectively, were 10.78degrees and 8.43degreesC, and total effective temperatures were 57.80 and 172.41 degree-days. Mean generation time (T-o) of the population ranged from 9.94 days at 35degreesC to 25.99 days at 20degreesC. The net reproduction rate increased from 66.99 female/female at 20degreesC to 92.19 female/female at 25degreesC, and decreased to 84.34 female/female at 30degreesC and to 12.04 female/female at 35degreesC. The highest r(m) occurred at 30degreesC (0.302 female/female/day) and the lowest at 20degreesC (0.161 female/female/day).