As in other Tetranychus species, both T. kanzawai and T. urticae undergo reproductive diapause induced by short-days and low temperatures. This study compares the diapause characteristics of populations of these two species from Taiwan with those from Kagoshima (southern Japan) and the Okinawa islands (southwestern islands). Our previous study (Takafuji et al., 2001, Appl. Entomol. Zool. 36: 177-184) showed that most T. kanzawai populations from Kagoshima exhibited more than 90% diapause at 15°C-9L15D, but the incidence of diapause in populations from the Okinawa islands was very low, and some exhibited no diapause even at 15°C. The present study shows that populations from central Taiwan, including those from the lowlands, exhibited a lower incidence of diapause than populations from Kagoshima, but a higher incidence than populations from the Okinawa islands. These results imply that the gene flow among populations in the lowlands and mountains maintains a higher incidence of diapause in Taiwan, but the diapause characteristic may have been eliminated by warm temperatures on the Okinawa islands, on which there are no high mountains. On the other hand, all populations of T. urticae from Kagoshima, Okinawa and Taiwan similarly exhibited a very low incidence of diapause.