Effects of constant and variable temperatures on development and reproduction of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae)

We focused on the influence of different temperature amplitudes on development and reproduction of the two-spotted spider mite, Tetranychus urticae Koch, at a 16: 8 (L: D) h photoperiod and 60-95 % RH. The temperature amplitudes varied from 0 to 24 degrees C in steps of 6 degrees C; i.e. 22 +/- 0, 22 +/- 3, 22 +/- 6, 22 +/- 9 and 22 +/- 12 degrees C. Temperature changed every 24 h between a low and an upper value, but without changing the average temperature (22 degrees C). The number of eggs laid by five females for 24 h was slightly lower at 22 +/- 12 degrees C than at constant temperature (22 +/- 0 degrees C), and egg hatchability differed among the five temperature regimes. Developmental time at 22 +/- 0 degrees C was shorter than that at 22 +/- 3 and 22 +/- 6 degrees C, but longer than that at 22 +/- 9 and 22 +/- 12 degrees C. The oviposition period, total fecundity per female and adult longevity gradually decreased with increasing amplitudes. Sex ratio was similar at all five temperature regimes. The intrinsic rate of natural increase (r(m)) was affected by temperature amplitude and the r(m)-values at all amplitudes except 22 +/- 12 degrees C were higher than that at constant temperature. Thus, this study showed that variable temperature regimes influence population growth rates of T. urticae and that large amplitude regimes are stressful for this species.