S. Mahunka szerk.: Folia Entomologica Hungarica 55. (Budapest, 1994)

From the species listed above, Prosactogaster erdoesi, Platygaster sp. and Torymus arundinis, as mentioned before, are presumably reared from Cecidomyidae living in the internodia below the galls. The role of Aprostocetus species is still unclear. The species Polemochartus melas emerged definitely from L. pullitarsis pupae. Hylaeus sp. is an inquiline Hymenoptera. Gasteruption kriechhaumeri is a parasitoid of a related inquiline. The occurrence of more than one species in a gall gives the difference between the number of infected galls (412, Table 2) and the total number of occurrences of all the species (421, Table 3). As it can be seen, with different feeding habits more than one Hymenopteran species can share one single gall. Inside the pupae of a gall-forming fly, however, always only the specimen (e.g. Polemochartus species) or specimens (e.g. Tetrastichus légionárius) of one parasitoid species developed, while the number of inquiline Hymenopteran species is not limited as much. Strong affinity exists only between the host and its parasitoid, while the criteria for the presence of other Hymenopteran species is only the gallproviding habitat and their food. The occurrence of Hymenoptera and Diptera together At the same time when Hymenopterans reared, numerous Dipterans emerged as well. Mostly they belong to the family of Chloropidae (Cryptonevra species), like the gall-forming Liparae, but there were species belonging to other families (e.g. Anthomyzidae), too. Generally, from one rearing pot several specimens of more than one Diptera species reared, which happened three times more than in the case of Hymenoptera. In half of the galls infected by Hymenoptera reared Diptera, too. The Diptera joined the assemblage thriving in the gall as a competitor for space and food. Actually, the strong relationship between these two insect orders exists only between host and parasitoid (Erdős 1957/?). The dipterological investigation of our collection consisting of thousands of specimens is in process, the result of which will be published elsewhere. THE ECONOMIC IMPORTANCE OF HYMENOPTERA The parasitoids reducing the density of the Lipara species population could play an important role in reed stands involved in reed management, where the gall flies are considered as pest, degrading the structure of the reed tissue, reducing the food resource of its rhysomes and the size of the reed plant (Dely-Draskovits et al. 1989). In such cases the reed stands can be effectively protected against the Lipara in a physical way e.g. by mowing yearly, by transporting the bundles of reed away before the rearing/swarming period, or by burning the reed stand. But, by doing so, not only the number of hosts is reduced, but their parasitoids, too. The activity of the parasitoids can be effective even in degrading stands, and it might be important in reed stands in bad condition, where the less immune reed is exposed to other pests. The results on the parasitoids developing in 9-10% of Lipara galls species population in Hungary, gives a very low average value of infection. However, this average is based on data varying in time and space from population to population of different sizes.