Ichneumon flies belong to the most important natural enemies of spruce webworm sawfly. Their effects are observed mainly in the latency period, when they are an efficient mortality factor. Ichneumon flies may influence the mortality rate of this pest also in the gradation period, when their relatively high fertility is gradually playing its role; thus they contribute to a reduction in the gradation population of spruce webworm sawfly. But there are very complex relations between these important parasitoids and spruce webworm sawfly due to complex bionomy of the host (diapause). Three types of localities were chosen to investigate the populations of spruce webworm sawfly and its parasitoids: in the area of gradation, in the area with low abundance of the pest for a long time, and finally in the area with mass outbreak of the pest several years ago and currently with pest latency. A method of using photoeclectors was applied for these investigations. Responses of ichneumon flies to increase in its host's abundance were different in the particular types of localities. In the area of gradation ichneumon flies flexibly increased their population density similarly like the host, but in the area of latency with the long-term low abundance of the pest they did not respond to the increase in pest's abundance while in the adjacent area of latency with the former, mass outbreak of the pest (high abundances of spruce webworm sawfly in 1984 and 1986) only two species of the main parasitoids (H. narrator, O. monticola) responded to the increase in pest's abundance. Fig. 1 clearly shows the responses of particular species. Analogical spectra of ichneumon fly species were determined in the particular types of localities (Tab. I). It is to note that the species spectrum of ichneumon flies at the Trest locality with applications of the EVISEKT 90 SP chemical to control the pest larvae was in fact similar to that of the adjacent locality Knezice. At the North Moravian locality Velke Pavlovice the swarming of spruce webworm sawfly began on average two to three weeks earlier than at both South Moravian localities (Trest, Knezice, Czech Republic). Flights of ichneumon flies had similar patterns at the particular localities, that means similar to its host's swarming patterns. Observations of spruce webworm sawfly swarming indicated food intake by the pest adults, and honeydew of aphids was found to be highly attractive. This kind of food was equally attractive to ichneumon fly adults and to their hosts; they were also found to consume pollen grains of blossoming grasses. Honeydew of aphids was available only in dry sunny weather. The adults of spruce webworm sawfly in laboratory breeding were administered highly concentrated sugar solution. The intake of this food did not for the time being influence either their life duration or female fertility. But the breeding comprised a relatively low number of individuals (17 males, 13 females). An interesting finding was an observed difference in the time of food intake in both sexes. The males licked the sugar solution for a short time only (1 - 2 min), but the females licked it even 10 minutes. The females were also laying eggs, 8 to 10. The adults of ichneumon flies of the species H. rufinus, H. narrator, X. fulvipes, X. mordax, O. monticola and E. erythrogaster were raised together with the larvae of spruce webworm sawfly in field conditions. Parasitism was successful only in the species H. narrator and H. rufinus. The species H. narrator mostly attacked the first instar of the host's larvae while H. rufinus attacked the second instar (estimate on the basis of the time of occurrence). Four adult larvae of these ichneumon flies (three larvae of H. narrator, one larva of H. rufinus) were raised from the parasitized larvae of spruce webworm sawfly at a laboratory. The life duration of adults raised in field conditions (ichneumon flies and spruce webworm sawfly) was between 10 and 14 days. An assessment of dominance in the particular species of ichneumon flies showed that H. narrator was the major parasitoid and H. rufinus ranked as the second. Higher abundance of O. monticola was observed at the localities Knezice and Trest. none