Assessment of Azorean native strains of Heterorhabditis bacteriophora for the biological control of Popillia japonica

Entomopathogenic nematodes (EPNs), especially Heterorhabditis bacteriophora, are promising candidates for biological control of Popillia japonica larvae. Thus, there is a need to study native strains to ensure biological agents adapted to specific environmental conditions to improve their effectiveness in field applications. This work aimed to test the pathogenicity of five Azorean isolates of H. bacteriophora strains to third-instar larvae of P. japonica under laboratory and semi-field conditions. All EPNs were able to quickly infect larvae with LT₅₀'s ranging between 3.66 and 4.54 days in controlled laboratory conditions. The semi-field experiment consisted of an EPN application in buried tubes containing five larvae each in May and October. After 15 days, larvae were recovered and confirmed for nematode parasitism. In May, Az29, Az148, Az170, and Az171 displayed a mean of 37% infected larvae per tube. In contrast, EPNs showed a lower infection ability during the experiment in October, and only Az148 maintained the number of parasitized larvae, with a proportion of 40% of infectivity. The results suggest that native EPNs, like Az148, could be better adapted to climatic and edaphic conditions to control P. japonica larvae.