The use of irradiated and cold-stored host eggs could be one option to facilitate the mass rearing of egg parasitoids to control lepidopteran pests. The effect on Trichogramma evanescens (L.) wasp quality after 3-month storage of host eggs of the Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and the Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechidae), that had previously been irradiated with gamma radiation, was investigated. Efficiency of T. evanescens was studied by measuring parasitization, adult and female emergence. There was no significant difference in parasitization and in adult and female T. evanescens emergence between gamma radiation doses and the untreated control for up to 30 days for E. kuehniella eggs and, thereafter they decreased drastically as the storage time increased for up to 60 and 30 days for E. kuehniella and S. cerealella eggs, respectively. No parasitization was observed when the eggs were stored longer and then offered to T. evanescens females. Data obtained from diapaused T. evanescens stored at 3 degrees C for 20, 70, 100 and 150 days indicated that pre-storage temperatures affected the induction of diapause. It was possible to induce diapause in developmental stages of T. evanescens by exposing the immature stages (prior to the pre-pupal stage) inside host eggs to 10 and 12 degrees C for 30 days. Under these conditions, parasitoids could be stored for a period of 50 days without adverse affects on emergence. Emergence appeared to decrease with an increase in the duration of storage for a period up to 150 days for the eggs of E. kuehniella. Parasitoids failed to enter diapause when pre-storage conditions were 3 and 7 degrees C for host eggs of both E. kuehniella and S. cerealella. The long-term storage of parasitoids in diapause improved the mass rearing potential for lengthened releases of this species.