Background and Purpose: Two leaf miners, Parectopa robiniella and Phyllonorycter robiniella (Lepidoptera, Gracillariidae), native to North America, were stablished in Europe. These two invaders provide an excellent opportunity to study the insertion of new species into an existing host-parasitoid community. The following hypotheses were tested:(i) parasitoids attacking the invaders have a wide rather than a narrow host range;(ii) the invading leaf-miner species on black locust are attacked by fewer species of parasitoids than endemic species;(iii) the parasitoid communities attacking invading species are most similar to those attacking endemic leaf-miners with similar ecology;(iv) how the parasitoid communities affect the population dynamics of invaders;(v) what is the difference between the Ph. robiniella and Pa. robiniella parasitoid communities.

Materials and Methods: Samples were taken at two sites in pure black locust stands: Gödöllõ (Pest county) and Visonta (Heves county) and in the western part of Hungary: Csorna, Koroncó, Lövõ (Gyõr-Moson-Sopron County). From each sampling site twenty 60 cm long branches were randomly cut and the first top 15 leaves were checked on each branch: the number of leaflets per leaves and the number of mines per each leaflet were counted. 300 mines of each leaf-miner species were chosen randomly from 10 trees in different canopy levels and were carried to the laboratory for further individual rearing.

Results and Conclusions: All the parasitoid species reared from these two leaf-miners are generalists–common and abundant species on different lepidopteran leaf-miners associated with oaks and other woody plants. In both, Ph. robiniella and Pa. robiniella, the same dominant species of parasitoids were reared. In Ph. robiniella the parasitoid species richness was slightly higher than in Pa. robiniella. The two invading leaf-miners, Ph. robiniella and Pa. robiniella, recruited a parasitoid community of nearly the same size as native Phyllonorycter species on oaks and this process of shifting onto new hosts was quite rapidly, during 10–20 years. The parasitoid communities of Parectopa are simpler than in Phyllonorycter, which is probably due to different mine structure and ecology of the two invading hosts.