Abstract
Overwintering sites and stages of Scirtothrips dorsalis HOOD were observed at tea fields in Kanaya, Shizuoka Prefecture, Central Japan from November, 1979 to April, 1980. Since the adults were collected from sites located in the leaf zone, branch zone, litter and soil throughout winter, it is assumed that the thrips hibernate in the adult stage. The adults showed minimum level of activity for three months from mid-December to mid-March, but some were active in the tea crown throughout the winter. The larvae which moved from leaves to tree trunks or litter pupated there, and most of them became adults from November to December, at least before February. However, the larvae, prepupae and pupae were also able to hibernate if young leaves were available in mild winter. In the present observation litter was selected as the most suitable site for hibernation (64.4%), followed by the branch zone (16.2%), soil (12.5%) and leaf zone (6.9%), but preference of the thrips for the overwintering sites may vary with the conditions of the tea fields. The female/male ratio of the adult insects during January to February was about 3.4 in tea bushes, and about 2.5 in litter and soil. The adults which had overwintered emerged from litter and moved to the leaf zone in late March after a few days of high temperature. After feeding on and laying eggs in new leaves, most of the adults died before the end of April and some before middle May. The life span of the overwintering adults appears to be about five months.
