Abstract: Elm spanworm egg parasite, Ooencyrtus ennomophagus Yoshimoto was introduced from the United States in 1981. The number of generations per year is from 7 to 8 in Hang Zhou. Overwintering as a mature larva within the host egg, the egg parasite parasitizes successfuly the eggs of pine lappet caterpillar, Dendrolimus punctatus Walker and the eggs of other 18 forest insect species. The adult stages of O. ennornophagus synchronize with occurrences of the eggs of D. punctatus. It hibernates and aestivates successfuly, and may be established or form populations in Zhejiang. O. ennomophagus is considered to be the potentially effective natural enemy against D. punctatus. In laboratory, eggs of the Dasychira baibarana Matsumura, D. axutha (Collette) and Redoa cygnopsis Collenette can be used as alternate hosts for the rearing of O. ennomophagus.