Trait Stability and Fitness of the Heat Tolerant Entomopathogenic NematodeHeterorhabditis bacteriophoraIS5 Strain

Natural populations of entomopathogenic nematodes may possess novel traits that offer advantages in biological control. If, however, the populations cannot be reared under laboratory conditions, and if their beneficial traits are unstable, then increases in biocontrol efficacy will be minimal. The stability of heat tolerance in, and fitness under laboratory conditions of, a newly discovered strain ofHeterorhabditis bacteriophora(designated IS5) were investigated. Trait stability and fitness assays were conducted after multiple passages throughGalleria mellonella.Assays were conducted on IS5 populations reared at 30 and 25°C. Trait stability was determined as survival at elevated temperatures. Relative to the commercially available strain ofH. bacteriophora(HP88), the IS5 strain exhibited greater heat tolerance after 12 passages regardless of selection pressure. The population of IS5 reared at 30°C exhibited greater heat tolerance than the population reared at 25°C. Results indicated that the heat tolerance trait is genetically based. Estimates of fitness were based on virulence, infectivity, reproductive potential, and storage capacity. The virulence, infectivity, and reproductive potential of IS5 nematodes were greater than or equal to that of HP88 nematodes. The heat tolerance trait in IS5 was retained after 6 weeks of storage. The IS5 strain survived significantly longer at 25°C than at 10°C, indicating that these nematodes may be cold sensitive. The results of this paper will expedite future genetic, biochemical, and field efficacy studies onH. bacteriophoraIS5.