Annual Life Cycle of the Two-Spotted Spider Mite, Tetranychus urticae KOCH(Acarina : Tetranychidae), on Ribes rubrum L. in Sapporo : The Presence of Non-Diapausing Individuals

Abstract

The annual life cycle of a Tetranychus urticae KOCH population on red currant plant, Ribes rubrum L., and diapause incidence of the populations from red currant and red clover, Trifolium pratense L., were studied in Sapporo, northern Japan. The mites appeared on leaves in late April, and the occurrence ended between mid-and late November when defoliation of the red currant leaves occurred completely. The population har 6 or 7 generations a year, but all stages were seen on the leaves in early winter. The photoperiodic responses of the populations from red currant and red clover were similar to each other, and the proportions of diapausing females reached 96 to 100% at 10 hr of light. In the field, the proportion of diapausing females did not reach 100% in the red currant and red clover populations even in early winter. These show that the red currant and red clover populations include the small number of non-diapausing individuals.