The egg parasite Ooencyrtus ennomophagus Yoshimoto (1975) is a good candidate for the biological control of certain defoliators. In 3 years it eliminated an outbreak of the elm spanworm, Ennomos subsignarius (Hübner), that reached from southeastern New York State across Connecticut and into Rhode Island (Kaya and Anderson 1974). Timely biological control, however, requires maintenance of parasite cultures in a laboratory for mass production when the need arises. Adults of O. ennomophagus live for about 3 months in the laboratory, but supplying them with suitable host material has been a problem. Drooz and Solomon (1980) found that the eggs of the factitious host, the notodontid Clostera inclusa (Hübner), could be stored at −10°C for a month and used for culturing O. ennomophagus. Tests under way indicate that the eggs may be stored longer than 12 months. I report here the development of O. ennomophagus in eggs kept at −10°C but not in fresh eggs of the pine looper, Lambdina pellucidaria (Grote and Robinson). The results indicate a potential for rearing parasites on treated eggs of non-host insects, if the need arises.