Entomopathogenic nematodes for biological control of Popillia Japonica larvae: current status and future prospects

The Japanese beetle (Popillia japonica Newman), first detected in Northern Italy in 2014, is considered one of the most dangerous quarantine pests for the entire European territory due to its potential environmental, economic, and social impact. As its larvae spend most of their life cycle in the soil, entomopathogenic nematodes (EPNs) offer a promising biological control option. Heterorhabditis bacteriophora (strain POP 16) was detected in the soil of outbreak area and selected as the most virulent native strain based on preliminary laboratory virulence assays. Field trials were conducted in the Piedmont region from 2021 to 2024 to assess POP 16's effectiveness in controlling the P. japonica larval population and its persistence in the soil. P. japonica larval populations were significantly reduced in plots treated with EPNs, with over 90% fewer larvae observed compared to untreated areas and H. bacteriophora persisted in the soil for up to two years after treatment. The effects of EPNs on non-target soil biota were also evaluated and no significant negative impacts were observed in EPN-treated soil compared to the control. However, some non-target edaphic arthropod taxa showed increased abundances, suggesting potential long-term changes in the soil ecosystem. Regarding the future prospects: identify the most promising symbiotic bacterial strains associated with EPNs for controlling P. japonica and study their genomes could reveal the loci responsible for entomopathogenesis. These further in-depth investigations are essential for developing novel, environmentally friendly control measures for the control of P. japonica, such as bioinsecticides based on bacterial strains isolated from EPNs.