Host-related differences in diapause characteristics of different geographical populations of the Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari : Tetranychidae), in Japan

The incidence of diapause in the polyphagous spider mite Tetranycnus kanzaw ai was determined fur 65 populations derived from deciduous and herbaceous hosts and for 33 populations from tea, at 3 temperatures under short-day co nditions. Most populations on the four main islands of Japan, irrespective of the host species on which they occurred expressed more than 90% diapause at 15 degreesC, whereas populations on the Okinawa islands exhibited a ver y low incidence or no diapause. The incidence of diapause decreased when te mperature was increased from 18 to 20 degreesC in populations from warmer a reas such as southern Kyushu and Honshu. This temperature-dependent decline in diapause incidence was most conspicuous in populations from Tanegashima and Yakushima Islands. The incidence of diapause at 20 degreesC tended to be lower in populations derived from tea than those from deciduous hosts in the same, warmer areas, showing that the former have a lower capacity for diapause. The present results, together with previously published data for T. urticae, showed that the lower temperature threshold for diapause induct ion was higher in T: kanzawai than in T. urticae and thus the clinal decrea se in diapause percentage occurred at much lower latitudes in the former at 20 degreesC.