Cold tolerance of steinernematid and heterorhabditid nematodes

1. Nematodes survive subzero temperatures using either a freeze-avoiding or freezing-tolerant strategy. Steinernema anomali, S. feltiae, and Heterorhabditis bacteriophora were all found to be freezing tolerant. 2. The lower lethal temperatures were -22, -19 and -14°C for S. feltiae, H. bacteriophora and S. anomali, respectively. 3. Survival after prolonged freezing at -4°C was 6, 5 and 3 days for S. feltiae, H. bacteriophora and S. anomali, respectively. 4. Acclimation to lower temperatures increased freezing tolerance. The freezing tolerance of Heterorhabditis bacteriophora increased under a stepwise acclimation regime; S. feltiae acclimated better under a direct acclimation regime.