Auswirkungen des Einsatzes entomopathogener Nematoden (Heterorhabditis sp.) im Freiland auf die Nichtzielfauna, 2. Teil: Diptera

The effects of entomopathogenic nematodes on nontarget Diptera of terrestrial ecosystems were investigated for the first time in the field. Experiments were conducted 1989 at four sites near Darmstadt (FRG) (mixed deciduous forest, forest border, orchard and summer wheat field). In field trials the nematode strainHeterorhabditis HL 81 was distributed at concentrations of 10⁶ ind./m² on plots of 100m² each. Diptera were sampled using emergence traps set on soil (photoeclectors) over a period of five to six weeks after nematode application. The obtained results demonstrate, that only in some cases an appreciable parasitation of Diptera by the employed nematode strain may have occurred. Only on one site (orchard) a significant reduction (α≦0,05) of several nontarget species of families was observed. On the contrary, in each of the four nematode plots some species or families emerged at higher rates compared with the untreated plots. Other causes for the unequal distribution of Diptera than the parasitation throughHeterorhabditis are discussed. The detrimental effects of a field application of entomopathogenic nematodes on the nontarget insect fauna must be considered negligible at the present state of knowledge.