Cold tolerance of entomopathogenic nematodes

Entomopathogenic nematodes in the Steinernematidae and Heterorhabditidae families are lethal parasites of insects They have great potential as biological control agents since they can be mass produced in vitro However their limited shelf life is the major impediment to their large scale commercial application Attempts to base a storage technology on partial desiccation and anhydrobiosis have met with limited success The natural capacity of entomopathogenic nematodes for freezing tolerance could be an alternative to be exploited as a first step towards developing a method for their longterm storage In the present laboratory experiments the entomopathogenic nematode Steinernema feltiae has shown to be freezetolerant if frozen at relatively high subzero temperature with survival near the level of controls However slow freezing at high subzero temperature (1C) enhanced the nematodes survival at lower temperatures (down to 12C) Freezing of the nematodes was confirmed under the cold stage microscope although the mechanism of survival in the slow freezing regime was difficult to visualise through cold stage microscopy This mechanism needs to be investigated further via a different technique such as freeze substitution and electron microscopy Neither acclimation nor rapid cold hardening improved the survival of nematodes significantly