We investigated the effect of temperature on development and demographic
parameters such as the intrinsic rate of natural increase (rm) of the two spider mite
species Tetranychus merganser Boudreaux and T. kanzawai Kishida at eleven constant
temperatures ranging from 15 to 40C at intervals of 2.5C. Both male and female
T. merganser and T. kanzawai completed development from egg to adult at temperatures
ranging from 15 to 37.5C. The longest developmental duration of immature stages was
found at 15C and the shortest developmental duration was found at 35C for both
species. Using linear and non-linear developmental rate models, the lower thermal
thresholds for egg-to-adult (female and male) and egg-to-egg development were estimated
as 12.2–12.3C for T. merganser and as 10.8C for T. kanzawai. The highest
developmental rates were observed at around 35C, whereas the upper developmental
thresholds were around 40C for both species. In fact, at 40C, a few eggs of either
species hatched, but no larvae reached the next stage. The rm-values of T. merganser
ranged from 0.072 (15C) to 0.411 day-1 (35C), whereas those of T. kanzawai ranged