The Impact of Parasitoids On Natural Populations of Temperate Woodland Drosophila

The species complex of temperate woodland Drosophila and its hymenopterous parasitoids was studied to elucidate the importance of parasitization as a mortality factor of Drosophila populations. A total of 5841 Drosophila and 801 parasitoids emerged from the collected field samples, indicating an overall parasitization rate of 12.1 %. Parasitization rates during a period of 9 weeks in midsummer were considerably higher, with a mean rate of 32.5 % . Parasitization rates in some substrate types, i.e. sap fluxes of wounded trees, ranged from 70% to 100%, indicating that risks of parasitization for Drosophila species that specialize on this substrate are very high, whereas parasitoids specialized on this microhabitat may experience high intra- and interspecific competition for hosts. It is concluded that parasitization is an important mortality factor during a considerable part of the Drosophila breeding season.