Supplementing the diet of Coeloides scolyticida, Dendrosoter protuberans and Ecphylus silesiacus (Hymenoptera: Braconidae) with Parker's diet and the nectars of melliferous plants: Daucus carota L., Sinapis alba L. and Stachys recta L. had a significant effect on longevity, reproduction, developmental rate, and parasitizing of Scolytus scolytus (Fab.), Scolytus multistriatus (Marsh.) and Scolytus pygmaeus (Fab.) (Coleoptera: Scolytidae). These values were considerably lower for wasps fed with the nectar of Sinapis arvensis L. and Trifolium repens L. and the lowest for those without dietary additives. Parker's diet had the most significant effect on the parasitoids and parasitizing of the bark beetles. Nectar of S. recta and S. alba proved most suitable for C. scolyticida and D. protuberans, while E. silesiacus using the nectar from D. carota flower significantly increased parasitizing of S. pygmaeus. T. repens flowers were not a suitable additive for the diet of parasitoids. The parasitoids without additives in their diet had shorter lives, shorter development, and were less effective in reducing host numbers. E. silesiacus wasps had the longest development, and C. scolyticida the shortest. Generally, the parasitoids of the second generation had a slightly prolonged development (1-2 days). none