In nine-year undisturbed field-bred populations, 137 individuals were obtained of the ichneumon wasps of the Xenoschesis fulvipes (Grav.) species and 75 individuals of the Ctenopelma nigrum Hlmgr. genus from the eonymphs of web-spinning sawflies of the genus Cephalcia Pz. of accurately known age. Both the above-mentioned larval parasites produced partial subpopulations with different time of development in the localities under study. The development of the X. fulvipes ichneumon wasp is annual to triennial in the territory of the Czech Socialist Republic. No four-year development type was recorded. Biennial subpopulation was found to be the most abundant in the given period of observation in nine of eleven cases. Annual development was the second most abundant (observed to be the most abundant in two cases of the drops of the host pest larvae and the second most abundant in three of eleven cases). The triennial development of the ichneumon wasp was always the least abundant. The ichneumon wasp X. fulvipes was always more abundant in the eonymphs of the hosts at lower altitudes (up to 700 m a. s. l.). At the highest-altitude site included in the study (840 m a. s. l.), this species occurred just sporadically as a parasite of web-spinning sawflies. Its population levels were also comparatively low in the sandy areas of South Bohemia (Stare Mesto pod Landstejnem). Individuals of this ichneumon wasp mostly hatched later than the other species of larval parasites of web-spinning sawflies, i. e. usually in the latter half of June to the beginning of July. The parasitation of the host population by this ichneumon wasp did not exceed 3.3%. At the site of the lowest altitude, the resultant parasitation reached a value up to 20%. Ichneumon wasp of the Ctenopelma nigrum Hlmgr. species hatched from the eonymphs of the web-spinning sawflies of the Cephalcia Pz. genus at altitudes up to 700 m a. s. l. It had the highest abundance at the lowest altitudes (up to 600 m a. s. l.). During the given period of observation, it developed within one to two years. Triennial development was not recorded in this species. The development of the majority of the individuals (two-thirds) had a biennial type of development. The Ctenopelma nigrum Hlmgr. ichneumon wasp is undoubtedly the most frequently hatching larval parasite of the spruce web-spinning sawfly. Parasitation of the host population by this species of ichneumon wasp does not exceed 4.2%. The resultant parasitation is 14% at the maximum. none