Abstract: Entomoparasitic nematodes of the species Heterorhabditis bacteriophora, highlyvirulent against larval stages of the Western corn rootworm in laboratory studies, were tested infield experiments in the south-eastern part of Austria. Diabrotica virgifera virgifera was firstrecorded at this field site in 2002, since then high population densities developed in fields withcontinuous corn. Nematodes were applied to small field plots in two different formulations,suspended in water and as granules without water, and tested against an untreated control andClothianidin coated seeds in five replicates. Maize plants were artificially infested withD. v. virgifera eggs to guarantee a homogenous pest population. Treatments were evaluated by(a) recording the emergence of adults in cages and (b) rating the damage of maize roots.Entomoparasitic nematodes significantly reduced the emergence of adult corn rootworms fromtreated plots, regardless of formulation. They were more efficient than the treatment of maizeseeds with Clothianidin. However, nematode treatments could not prevent root damage, whereastreatment of seeds with Clothianidin was able to keep root damage below the economicthreshold. Reasons for these contradictory results are discussed.