Impact of the invasion of Popillia japonica on the community of soil entomopathogenic nematodes and native white grubs in Italy

Soil dwelling entomopathogenic nematodes (EPNs) are important natural enemies of insect pests of plant roots. Relationships between nematodes associated with the soil of hay meadows and grubs have been explored in the invasion area of the Japanese beetle Popillia japonica Newman (Coleoptera: Scarabaeidae) in northern Italy. Several species of indigenous white grubs are present in the territory and they are assumed to be associated with local EPN strains, mainly belonging to Heterorhabditis, Steinernema and Oscheius spp. The presence of P. japonica could affect the ecological balance between native grub species and the EPNs. To test this hypothesis, the spatial distributions of EPNs, native grub species and P. japonica in the invaded area of the Japanese beetle were explored. The EPN strains were tested against P. japonica in the laboratory under different stress conditions and all EPN strains showed capacity to exploit P. japonica as host. EPNs were more frequently isolated from soil samples collected in the early colonized sites. The native species of grubs did not seem to be dramatically affected by the increase of EPN density associated with the expansion of P. japonica.