Genetic Enhancement of Environmental Stability and Efficacy of Entomopathogenic Nematodes for Biological Control

Abstract

The overall obejctive of the research project was to enhance the intrinsic biological control potential of entomopathogenic nematodes through genetic manipulation. We have chosen heat and desiccation tolerance as prime traits to be enhanced in order to increase the overall efficacy of these nematodes against insect pests under harsh conditions. Initially, we used mutagenesis and selection approaches to enhance these traits. In the mutagenesis experiments several morphological mutants of Heterorhabditis bacteriophora HP88 were isolated and characterized phenotypically and genetically. Infective juveniles of H. bacteriophora HP88 were subjected to heat and desiccation selection regimes for several generations. Small increase was recorded, after 4 and 6 rearing cycles for both traits. However, in both selection regimes a significant deterioration in the reproductive capability of the nematodes was observed. In a screen of new nematode populations, from arid regions in Israel, a heat tolerant (IS5 strain) and desiccation tolerant (IS6 strain) were isolated. Both strains were taxonomically identified and their beneficial characteristics (environmental tolerance, insecticidal virulence and reproduction) were determined. We further investigated the stability of the enhanced heat tolerance trait in, and the storage capacity of, the newly discovered IS5 strain. Genetic studies demonstrated that the heat tolerance of the IS5 strain is genetically based and is dominant. The trait for heat tolerance was transferred from the IS5 strain to the HP88 strain of H. bacteriophora. The transfer was accomplished by allowing the heat tolerant strain (IS5) to mate with the commercial strain (HP88). The hybrid nature of the progeny was confirmed using a recessive marker mutant of the HP88 strain (H-dpy-2). We have used (RAPD-PCR) to compare genetic variation in the IS5 and the HP88 strains of H. baceriophora. The results indicated that genetic variation in the HP88 was significantly less than in the IS5 strain which was recently isolated from the field. The new IS5 strain may be used as an effective biological control agent in warm environments. In addition, IS5 can be used as a genetic source for cross-hybridization with other H. bacteriophora strains.