Thyrassia penangae (Moor) a serious pest of Japanese cayratia herb (Cayratia japonica). It generally occurred 4～5 generations each year in Nanchang, hibernating as prepupae in cocoons. There were always some individuals entering diapause in each generation. Thus, some individuals with a summer diapause only produce two or three generations each year. The overwintering individuals emerged from cocoons from early May to late May. Females need to feed on nectar before laying eggs. Females laid 10 to 20 eggs each cluster at the back of the young tender leaves in the first generation and mainly on squares in the other generations. The mean fecundity per female was 43 eggs. Larvae mainly feed on leafbuds, tender growing terminals or young leaves in the first generation and squares in other generations. There were four larval instars. Under natural conditions, developmental duration was 4～7 days in egg stage, 10～14 days in larval stage, and 8～12 days in pupal stage. Non-dipause cocoons had 8～11 days of life span （the duration from prepupa to adult emergence）. The life span of aestivating and hibernating cocoons ranged from 32 to 40 days and 205 to 224 days, respectively. Longevity of adults ranged from 3～13 days.