none Calliphora vicina; PHYSIOLOGICAL-CONDITION; Stress as possible reaction to hymenopteran parasite during larval diapause; DIAPAUSE-; Larva, possible reaction to hymenopteran parasite; HYMENOPTERAN-PARASITES; Alysis manducator; Host larval diapause reaction, possible stress relationships Alysia manducator; DIPTERAN-HOSTS; Calliphora vicina; Host developmental reaction to parasite It was known that effect of injury caused by the parasitoid Alysia manducator during oviposition resulted in interruption of larval diapause and the puparium formation in Calliphora vicina. It was important to distinguish an indirect stress effect caused by parasitization and true parasitoid regulation of the host's physiology. Using some manipulations (burning or pricking the host's cuticle by the pin, interrupted oviposition, isolation of parasite in the host's body, the ligation experiments) it was shown that effect of interraption of host's diapause and the puparium formation have been induced by the developing parasite larvae, but not by stress of parasitization. Haematological data confirmed this conclusion. The experiments with ligations shown that induction of the host's pupariation did not require the participation of its endocrine centers. Histological investigation of some host's tissues indicated that parasitization provoked only the puparium formation and blocked the pupation (metamorphosis). Interaction of both the effects, i. e. the pupation blocking and the induction of the puparium formation, constitute the mechanism of host regulation, which provides for the parasitoid's active role in developmental synchrony.