Rapid Genetic Deterioration of Environmental Tolerance and Reproductive Potential of an Entomopathogenic Nematode during Laboratory Maintenance

Inadvertent selection is an important genetic problem frequently inflicted during laboratory culture and maintenance of biological control agents. Entomopathogenic nematodes can be maintained in the laboratory in three ways: cryopreservation in liquid nitrogen, storage at cold temperature with as few subcultures as possible, or storage at room temperature with frequent subcultures. We determined the influence of these laboratory maintenance regimes on the stress tolerance (UV, heat, and desiccation) and physiological fitness (storage stability, reproduction potential, and virulence) of a newly isolated strain GPS11 of Heterorhabditis bacteriophora. Except for desiccation tolerance, no detectable changes occurred with nematodes that were cryopreserved in liquid nitrogen for 1 year. Significant reduction in nematode heat, UV, and desiccation tolerance, storage stability, and reproductive potential occurred after only three passages in Galleria mellonella. The decline in nematode reproduction, storage stability, and stress tolerance was correlated with the increase in passage number. Increase in nematode virulence was observed when they were subcultured frequently in G. mellonella at room temperature. These results demonstrate that laboratory adaptation can produce dramatic changes in important biological attributes of entomopathogenic nematodes.