A comparative study of development and demographic parameters of Tetranychus merganser and Tetranychus kanzawai (Acari: Tetranychidae) at different temperatures.

We investigated the effect of temperature on development and demographic parameters such as the intrinsic rate of natural increase (r (m)) of the two spider mite species Tetranychus merganser Boudreaux and T. kanzawai Kishida at eleven constant temperatures ranging from 15 to 40°C at intervals of 2.5°C. Both male and female T. merganser and T. kanzawai completed development from egg to adult at temperatures ranging from 15 to 37.5°C. The longest developmental duration of immature stages was found at 15°C and the shortest developmental duration was found at 35°C 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 12.2-12.3°C for T. merganser and as 10.8°C for T. kanzawai. The highest developmental rates were observed at around 35°C, whereas the upper developmental thresholds were around 40°C for both species. In fact, at 40°C, a few eggs of either species hatched, but no larvae reached the next stage. The r (m)-values of T. merganser ranged from 0.072 (15°C) to 0.411 day(-1) (35°C), whereas those of T. kanzawai ranged from 0.104 (15°C) to 0.399 (30°C). The r (m)-values were higher for T. kanzawai than for T. merganser at temperatures from 15 to 30°C, but not at 35°C (0.348 day(-1)). Total fecundity of T. merganser was also higher than that of T. kanzawai at 35°C. These results indicate that higher temperatures favor T. merganser more than T. kanzawai.