none Factors affecting the envenomation by the parasitoid, B. brevicornis Wesmael, were investigated; venom doses, ratios of host larvae exposed to a single female and size of host larvae. No permanently paralyzed larvae of Sesamia cretica were observed before 0.5 h of exposure to the parasitoid. This was true, even when 1 host larva was exposed to 8 adult females. Increasing the numbers of females kept with 1 host larva resulted in increased numbers of immobilized larvae, especially during the first 3-4 h. The latter was reliable even with 6 females/larva, thereafter differences was not significant. The number of completely paralyzed larvae increased with an increase in numbers of host larvae exposed to a single female, especially after 2 days. Within the same species, large host larvae were significantly less sensitive to the parasitoid's venom than small larvae during 6 h exposure, respectively.