Comparison between TT01 and GPS11 strains of the entomopathogenic nematode Heterorhabditis bacteriophora

The TTO I strain of Heterorhabditis bacteriophora is emerging as a model system for studies on entomopathogenic nematodes because of the completion of its genome sequence and demonstration of RNA interference based functional genomics. However, there is little information on its biology, ecology and biological control potential. Therefore, we compared ITO I infectivity to Galleria mellonella larvae in sand columns, infectiousness using the one-on-one sand-well bioassay, virulence (both nematode and symbiotic bacteria) to three different white grub species (Popillia japonica, Cyclocephala borealis and Rhizotrogus majalis), reproductive potential in G. mellonella, desiccation tolerance, and heat resistance with the commercial strain GPS II as a benchmark standard. Both strains showed similar infectivity in the sand columns but GPSII showed higher infectiousness against G. mellonella and greater virulence against all three white grub species than ITO I. Although, the symbiotic bacteria of the two strains are different (Photorhabdus luminescens subsp. laumondii for TTOI and P. temperata subsp. stackebrandtii for GPS II), there were no differences in the virulence of the bacteria against any of the three white grub species. The TTOI strain showed higher desiccation tolerance when dehydrated in 25% glycerol solution for 48 h and higher heat tolerance at 40°C for 6 h with or without preconditioning at 37°C for 24 h than the GPS 11 strain. These differences in desiccation and heat tolerance may be attributed to the climatic differences in the original localities of the two strains, with TTOI from a tropical climate and GPSll from a temperate climate. Further studies on biology including dauer formation and recovery, sex determination, immune defense, mass culture and survival in formulations, field persistence, and efficacy against additional insect pests are needed to develop baseline information on the TTO I strain to fully exploit its genome sequence information.