Impact of Constant and Fluctuating Temperatures on Population Characteristics of Tetranychus pacificus (Acari: Tetranychidae).

To understand the effect of fluctuating temperature on the population characteristics of Tetranychus pacificus, we determined their life tables under constant temperatures between 10 and 35°C and fluctuating temperatures (12 h per day at each of 5°C above and 5°C below the corresponding constant temperature). Tetranychus pacificus eggs did not hatch when held at a constant temperature of 10°C, whereas 77.6% of the T. pacificus eggs reached an adult life stage at fluctuating temperature 10°C ± 5°C. Female preadult development was faster under fluctuating temperatures 12.5, 15, and 20°C than under constant temperatures, whereas it was not significantly different at temperatures ≥ 22.5°C. The lower developmental thresholds (T0) for female preadult development were 10.24 and 5.73°C for the constant and fluctuating temperatures, respectively, while the thermal summations (K) were 215.10 and 265.64 degree days, respectively. The net reproductive rates (R0) at constant temperatures 15 and 35°C were significantly higher than those at the corresponding fluctuating temperatures. However, for 20, 25, and 30°C, the R0 values were not significantly different between constant and fluctuating temperatures. The intrinsic rate of increase (r) and finite rate of increase (λ) at fluctuating temperatures 10, 20, and 30°C were higher compared to the corresponding constant temperature. However, the values of r and λ at constant 25 and 35°C were higher than those at fluctuating temperature. The differential responses of life history between constant and fluctuating temperatures help to understand the population dynamics of T. pacificus under natural conditions.