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 degrees C and fluctuating temperatures (12 h per day at each of 5 degrees C above and 5 degrees C below the corresponding constant temperature). Tetranychus pacificus eggs did not hatch when held at a constant temperature of 10 degrees C, whereas 77.6% of the T. pacificus eggs reached an adult life stage at fluctuating temperature 10 degrees C +/- 5 degrees C. Female preadult development was faster under fluctuating temperatures 12.5, 15, and 20 degrees C than under constant temperatures, whereas it was not significantly different at temperatures >= 22.5 degrees C. The lower developmental thresholds (T-0) for female preadult development were 10.24 and 5.73 degrees 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 (R-0) at constant temperatures 15 and 35 degrees C were significantly higher than those at the corresponding fluctuating temperatures. However, for 20, 25, and 30 degrees C, the R-0 values were not significantly different between constant and fluctuating temperatures. The intrinsic rate of increase (r) and finite rate of increase (lambda) at fluctuating temperatures 10, 20, and 30 degrees C were higher compared to the corresponding constant temperature. However, the values of r and lambda at constant 25 and 35 degrees 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.