S. Mahunka szerk.: Folia Entomologica Hungarica 57. (Budapest, 1996)

which indices are considerably lower than those of the old stands, namely 40-55%. Similar indices were found in the oak forest stands at Gödöllő. Our samplings show an essential difference between the braconid species assemblages of the three oak forests each at Csobánka and Gödöllő. In the two oak woods a total of 49 species had been captured. From among the 49 species 19 were listed in both forests (i.e. 30 species occurred only either at Csobánka or Gödöllő), the difference in Jaccardindex figures 38.8%. On the basis of our three-year investigation the difference of the species assemblages between the two oak forests is considerable. However, it is reasonable to suppose that the true natural conditions show a less difference in this respect. The majority of the 49 braconid species in question are certainly living in both oak forests at Csobánka and Gödöllő on the one hand and our three-year collecting period was very short as well as our collecting method was not the most appropriate one, on the other, to attain the approximately full number of the braconid species living in the two forests. 3. Low differences were ascertained between the mixed (i.e. approaching the natural condition) and the pure (i.e. influenced by the forestry activity) oak forest stands of the same area (Csobánka and Gödöllő, respectively) concerning their braconid species assemblages. In the two pure oak forests, surprisingly, somewhat more species were trapped than in the two mixed oak forests (29 and 24 versus 27 and 22, see also Table 2). Supposedly this numerical species composition does not reflect the natural condition owing to the short-termed collecting time-period (i.e. two weeks each) in June and August 1992-1994. With our investigation we obtained the first insight and the first qualitative data of the braconid composition prevalent in the two oak forests. A comparison of the species identity of the braconid assemblages of the mixed and pure oak forests at Csobánka and Gödöllő presented the following values expressed in percentages (Table 3). The percentage values unambiguously indicate higher differences between the mixed and pure old oak forests than between the mixed as well as between the pure old oak forests of the two areas. The species heterogeneity of the mixed and the pure old oak forests expressed by the Simpson-index is as follows: Csobánka mixed oak forest: D = 0.91; pure oak forest: D = 0.89; Gödöllő mixed oak forest: D = 0.83; pure oak forest: D = 0.90. The D-values unambiguously indicate that the heterogeneity of the braconid species assemblages in the different forests are high and numerically stand to each other. 4. From the viewpoint of the phenology of the braconid wasps in the study areas of Csobánka and Gödöllő the species may be separated into two groups according to their permanent as well as their temporary presence during the vegetation period in one year, on the one hand, and during the three years of investigation, on the other. The majority of the species is characterized by their seasonal presence within one vegetation period, and a fraction of the species was present during (nearly) the entire vegetation period. Almost every species of the first group was fairly permanently present during the three years. a) All in all, ten braconid species were sufficiently regularly trapped in 1992-1994 in a specimen numbers above five several times pro samplings. From among them one species, Microplitis mandibulator, was present in every sampling equally in the mixed and the pure old oak forests Csobánka and Gödöllő. Two species, Cotesia tibialis and