Testing Heterorhabditis bacteriophora to control Popillia japonica larvae in infected pastures in S. Jorge Island at the Azores

Abstract: The entomopathogenic nematode Heterorhabditis bacteriophora has been shown to effectively control P. japonica larvae in field assays. However, the efficacy of such applications depends on the environmental conditions, the time of application, the mode of application, and the dose of infective juveniles (IJ) applied. Furthermore, it is determinant the persistence of applied IJ in the soil to search and find suitable hosts. To test the efficacy and the persistence of 3 strains of H. bacteriophora in S. Jorge Island, we selected pastures with quite the same pest densities, close environmental conditions, and altitude, to perform the five field trials. We used 3 strains of H. bacteriophora, one isolated on the Island of S. Jorge (Az29), and two imported strains. Trials were done at the beginning of the insect cycle in soil, in the fall, and at the end of the soil cycle, in May. Significant differences were observed in the efficacy of nematodes at these two moments. The larval reduction was very low in fall applications either in treatments with the local and introduced strains. Applications in May reduced about 50 % of larvae in plots treated with local strain. The commercial strain caused a reduction of 45 %, not significantly different from the local strain. This data shows that the application of H. bacteriophora in May can reduce the population of P. japonica. We checked the persistence of applied strains in the field and only the local strain was detected 1 year after application, but in a single plot of the assay. Our data indicate that the local strain can be a good controller, but it must be formulated to increase persistence.