Entomoparasitic nematodes for control of the Western Corn Rootworm, Diabrotica virgifera virgifera

Entomoparasitic nematodes of the species Heterorhabditis bacteriophora, highly virulent against larval stages of the Western corn rootworm in laboratory studies, were tested in field experiments in the south-eastern part of Austria. Diabrotica virgifera virgifera was first recorded at this field site in 2002, since then high population densities developed in fields with continuous 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 and Clothianidin coated seeds in five replicates. Maize plants were artificially infested with D. 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 from treated plots, regardless of formulation. They were more efficient than the treatment of maize seeds with Clothianidin. However, nematode treatments could not prevent root damage, whereas treatment of seeds with Clothianidin was able to keep root damage below the economic threshold. Reasons for these contradictory results are discussed.