Potentially entomopathogenic nematode isolated from Popillia japonica: Bioassay, molecular characterization and the associated microbiota

The Japanese beetle, Popillia japonica Newman (Coleoptera Scarabaeidae), is a highly invasive pest recently introduced in Europe. In the current study a nematode is isolated from the third larvae instar of P. japonica collected in northern Italy. Both BLAST search and the phylogenetic maximum likelihood tree inferred from 18S rRNA sequences confirm the attribution of the isolated nematode to the genus Oscheius (Nematoda Rhabditidae). The entomopathogenicity of the isolated nematode was tested on larvae of the model organism Galleria mellonella L. (Lepidoptera Pyralidae). The mortality of the host after five days varied from 54% to 60%, depending on nematodes concentration. Furthermore, the microbiota associated with the isolated nematode was characterized using a metabarcoding approach. Our results suggest that the bacterial community of the isolated nematode is dominated by bacteria belonging to the genus Ochrobactrum, that includes entomopathogenic species. Further studies are needed to test the possibility of using this nematode as a biocontrol agent of P. japonica in Europe.