TRAIT STABILITY AND FITNESS OF THE HEAT TOLERANT ENTOMOPATHOGENIC NEMATODE HETERORHABDITIS-BACTERIOPHORA IS5 STRAIN

Natural populations of entomopathogenic nematodes may possess novel tr aits that offer advantages in biological control. If, however, the pop ulations cannot be reared under laboratory conditions, and if their be neficial traits are unstable, then increases in biocontrol efficacy wi ll be minimal. The stability of heat tolerance in, and fitness under l aboratory conditions of, a newly discovered strain of Heterorhabditis bacteriophora (designated IS5) were investigated. Trait stability and fitness assays were conducted after multiple passages through Galleria mellonella. Assays were conducted on IS5 populations reared at 30 and 25 degrees C. Trait stability was determined as survival at elevated temperatures. Relative to the commercially available strain of H. bact eriophora (HP88), the IS5 strain exhibited greater heat tolerance afte r 12 passages regardless of selection pressure. The population of IS5 reared at 30 degrees C exhibited greater heat tolerance than the popul ation reared at 25 degrees C. Results indicated that the heat toleranc e trait is genetically based. Estimates of fitness were based on virul ence, infectivity, reproductive potential, and storage capacity. The v irulence, infectivity, and reproductive potential of IS5 nematodes wer e 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 sur vived significantly longer at 25 degrees C than at 10 degrees C, indic ating that these nematodes may be cold sensitive. The results of this paper will expedite future genetic, biochemical, and field efficacy st udies on H. bacteriophora IS5. (C) 1996 Academic Press, Inc.