Actual and potential role of parasitoids (Hymenoptera: Eulophidae) in control of water-lily beetle Galerucella nymphaeae (Coleoptera: Chrysomelidae) in conditions of Botanical Garden of P.J. Šafárik University in Košice (Slovakia).
In the Botanical Garden of P.J. Šafárik University in Košice the water-lily beetle Gallerucella nymphaeae has been causing serious problems in growing ornamental cultivars of waterlilies Nymphaea × hybrida. When looking for possibilities of natural regulation of the beetle, the occurrence of egg parasitoids has been found with predominance of Oomyzus gallerucae. Later on, the occurrence of Aprostocetus celtidis has been noticed occasionally and the structure of hatching results suggests the possibility of its hyperparasitic relationship with O. gallerucae. This is the first record of association of these chalcid wasps to G. nymphaeae as well as the first ever registered species of parasitoids of the water-lily beetle eggs. During summer of 2012, the parasitation rate had been watched in three consequent extensive sampling events. The rate of parasitized eggs from individual basins varied from 2% to 29%, 12% being average. To compare, and potentially to enrich the spectrum of parasitoids in biological control of water-lily beetles in BG PJŠU, the nearest known natural habitats with occurrence of G. nymphaeae were visited near Klin nad Bodrogom. The samples of water-lily beetles provided pupal parasitoids - species Asecodes lucens and Tetrastichus clito, which have not been found from Košice samples yet. In the case of T. clito, it is another first ever record of parasitic relationship of this species with the water-lily beetle G. nymphaeae. From the faunistic point of view, all four species of chalcid wasps were recorded in Slovakia for the first time. Three newly registered associates (O. gallerucae, A. celtidis and T. clito) of G. nymphaeae will need further evaluation. According to literary sources, the typical regulator of the water-lily beetle seems to be A. lucens. Its introduction to BG PJŠU could significantly help in the biological protection of water-lilies grown there. The possibility of wider application of all parasitoids should be studied with regard to occurrence of alternative hosts on vegetation around the basins. As the registered eulophid species behave as generalist parasitoids, the differences in their chrysomelid hosts (and other parasitoids in the case of A. celtidis) and associated food plants should be taken into account in next research there.