Abstract
Seasonal trends in population density and diapause attributes in Tetranychus viennensis ZACHER on deciduous oak, Quercus mongolica var. grosseserrata (BLUME), were studied in Sapporo, Hokkaido. The mites occurred from early June to mid-October and were estimated to pass four generations per year. This active period corresponded with the phenology of deciduous oak. The number of mites showed a hump-shaped fluction like that of the predacious mite, Amblyseius finlandicus (OUDEMANS), but their occurrences seemed to be independent of each other. The photoperiodic response curve of this species was long-day type, and the critical photoperiod was between 14.0 and 14.5hr at 18°C. Diapause was induced in late August, while corresponded with the timing predicted by the critical photoperiod mentioned above. Diapause females collected after mid-November began oviposition, and the number of days to oviposition after incubation gradually decreased with the progress of collection time. Moreover, the number of females which oviposited gradually increased, although it did not reach 100%. Thus the termination time of diapause could not be determined. These results were compared with the data on apple orchards and on deciduous oak reported by other authors.
