Pathogenicity of four entomopathogenic nematode strains against Asian corn borer, Ostrinia furnacalis (Guenee), in Vietnam

The virulence and reproductive capacity of four indigenous entomopathogenic nematode (EPN) strains, S-PQ16 (Steinernema sp. PQ16), S-TX1 (Steinernema sangi TX1), S-DL13 (S. siamkayai DL13) and H-NT3 (Heterorhabditis indica NT3), against the last instar larvae of Asian corn borer (ACB), was evaluated. With moderately low concentrations of infective juveniles (IJ) from 10 to 100 IJ insect(-1), the ACB larvae were found to be susceptible to all four EPN nematode strains after exposure for 24, 48, 72, 96 and 120 h. The 100% mortality of ACB larvae by these indigenous EPN strains occurred after 96-120 h of exposure. The low LC50 values (between 21.7 and 27.9 IJ) indicated the high virulence of these four EPN strains to ACB larvae. The highest yield of IJ produced inside the insect cadavers for S-PQ16, S-TX1, S-DL13 and H-NT3 was 215.0 +/- 6.5 x 10(3), 83.1 +/- 4.9 x 10(3), 67.8 +/- 7.2 x 10(3) and 225.2 +/- 6.4 x 10(3) IJ, respectively, with low inoculated concentrations of between 30-50 IJ. The results, showing a high degree of virulence and high reproduction capacity, suggest that these indigenous EPN strains have great potential for biological control of the Asian corn borer.